Pitch is the perceived quality of sound that is proportional to its frequency.
What determines the pitch of sound?
The frequency of a note determines its pitch. When the vibrations of two notes with the same amplitude heard on the same instrument are of different frequencies, their pitch will differ.
What is meant by noise pollution? Name one source of sound causing noise pollution.
Noise pollution is the disruption caused by unwelcome loud and unpleasant sound with a decibel level greater than 120 dB coming from different sources in the surroundings, such as a loudspeaker,...
What is the safe limit of sound level in dB for our ears?
The safe sound level for our ears is up to 120 decibels.
Name the unit used to measure the sound level.
The decibel is the unit used to measure sound levels.
Express the power (with sign) of a concave lens of focal length 20 cm.
Solution: The expression for the power of lens is P = 1 / F According to the question, it is a concave lens so focal length will be negative. Upon substituting values, we get => P = 1 / - 0.2 m...
A concave lens forms an erect image of 1/3rdsize of the object which is placed at a distance 30 cm in front of the lens. Find:
(a) The position of image, and (b) The focal length of the lens. Solution: According to the question, Distance of the object u is – 30 cm And the concave lens forms an erect image of 1/3...
A convex lens forms an inverted image of size same as that of the object which is placed at a distance 60 cm in front of the lens. Find:
(a) The position of image, and (b) The focal length of the lens Solution: (a) According to the question, the convex lens forms an inverted, real image of the same size as the object. So,...
An object is placed at a distance of 20 cm in front of a concave lens of focal length 20 cm. find:
(a) the position of the image, and (b) the magnification of the image Solution: According to the question, Object distance is u = – 20 cm Focal length is f = – 20 cm (concave lens) (a) Expression...
A lens forms the image of an object placed at a distance of 45 cm from it on a screen placed at a distance 90 cm on the other side of it. (a) name the kind of lens. (b) find:
(i) the focal length of lens, (ii) the magnification of the image. Solution: According to the question, Object distance is u = – 45 cm Image distance is v = + 90 cm (a) Since the image is formed on...
A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find:
(i) the focal length, (ii) the magnification, and (iii) the nature of image. Solution: According to the question, Object distance is u = – 15 cm Image distance is v = – 60 cm (i) We know that the...
An illuminated object lies at a distance 1.0 m from a screen. A convex lens is used to form the image of object on a screen placed at distance 75 cm from the lens. Find: (i) the focal length of lens, and (ii) the magnification.
Solution: According to the question, Image distance is v = 75 cm Object distance is u = -25 cm The expression for Lens formula is - 1 / v – 1 / u = 1 / f Upon substituting values, we get 1 / f = 1 /...
The bells of a temple are big in size. Why?
Larger bells, according to bell research, have a lower resonance frequency. For a sound wave to travel great distances, the frequency of the sound must be lower. It's also been noticed that the...
State three factors which affect the loudness of sound heard by a listener.
The following elements influence the loudness of sound heard by a listener: (i) The square of the amplitude determines the loudness. (ii) Loudness is inversely proportional to distance squared....
Comment on the statement ‘loudness of sound is a subjective nature, while intensity is an objective nature’
The quantity of sound energy travelling per second typically across a unit area at a point of the medium is the intensity of a sound wave at that location. The intensity of a sound, or the energy...
How is the loudness of sound related to the intensity of wave producing it?
The formula for the relationship between loudness L and intensity I is \(L=K{{\log }_{10}}I\) where K is the proportionality constant
Define the term intensity of a sound wave. State the unit in which it is measured.
The quantity of sound energy travelling per second typically across a unit area at a point of the medium is the intensity of the sound wave at that location. The sound wave's strength is measured in...
Why is the loudness of the sound heard by a plucked wire increased when it is mounted on a soundboard?
Because the board covers such a vast surface and causes a large volume of air to vibrate, the sound energy reaching our ears is increased.
Name the unit in which the loudness of sound is measured?
The decibel scale is used to measure the loudness of sound.
How does the wave pattern of a loud note differ from the soft note? Draw a diagram.
The wave pattern of a loud note differ from the soft note in many aspects.
Two waves of the same pitch have amplitudes in the ratio 1:3. What will be the ratio of their (i) loudness (ii) frequencies?
(i) The square of the amplitude determines the loudness. The loudness ratio is 1:9. (ii) If the pitch remains constant, the frequency remains constant. 1: 1 ratio of frequencies
If the amplitude of a wave is doubled, what will be the effect on its loudness?
Because the square of the amplitude is exactly related to the loudness of sound. When the wave's amplitude is doubled, the sound becomes four times louder.
(a)Which of the following quantity determines the loudness of a sound wave?
(i)Wavelength
(ii) frequency and
(iii) amplitude
(b)How is loudness related to the quantity mentioned in the above part (a)
(a) The loudness of a sound wave is determined by its amplitude. A loud sound has a higher amplitude, while a quiet sound has a lesser amplitude. (b) The amplitude is proportional to the square of...
Name three characteristics of a musical sound.
Sound has three distinct properties. (i)Distinction (ii) shrillness or pitch (iii) Timber quality
A tuning fork of frequency 256 Hz will resonate with another tuning fork of frequency:
a. 128 Hz
b. 256 Hz
c. 384 Hz
d. 512 Hz
A tuning fork with a 256 Hz frequency will resonate with another tuning fork with a 256 Hz frequency.
When a body vibrates under a periodic force, the vibrations of the body are:
(a) natural vibrations
(b) Damped vibrations
(c) Forced vibration
(d) Resonant vibrations
The vibrations of a body are forced vibrations when it vibrates under a periodic force.
A wire stretched between two fixed supports is plucked exactly in the middle and then released. It executes (neglect the resistance of the medium):
(a) Resonant vibrations
(b) natural vibrations
(c) Damped vibrations
(d) Forced vibrations
Between the two fixed supports, a wire is stretched, plucked exactly in the centre, and then released. It works with natural vibrations
How do you tune your radio set to a particular station? Name the phenomenon involved in doing so and define it.
To tune a radio receiver, we simply change the settings of the electrical components such that vibrations of the same frequency as the radio waves we wish to receive are produced. Due to resonance,...
Why are the stringed instruments like guitar provided with a hollow sound box?
The sound box is designed such that the air column inside it has the same natural frequency as the string stretched on it, so that when the strings vibrate, the air column inside the box is forced...
When a troop crosses a suspension bridge, the soldiers are asked to break their steps. Why?
While the troops march in formation, all of their individual periodic forces are in phase, causing forced vibrations of a certain frequency to be created in the bridge. If the bridge's natural...
In figure A, B, C and D represent the test tubes each of height 20 cm which are filled with water up to heights of 12 cm, 14 cm, 16 cm and 18 cm respectively. If a vibrating tuning fork is placed over the mouth of test tube D, a loud sound is heard.
(a) Describe the observations with the tubes A, B and C when the vibrating tuning fork is placed over the mouth of these tubes.
(b) Give the reason for your observation in each tube.
(c) State the principle illustrated by the above experiment.
(a) The tubes A and C produce no loud sound, while the tube B produces a loud sound. (b) The frequency of the air column in tube D is the same as the tuning fork's frequency. Tube B has a resonance...
A vibrating tuning fork, held over an air column of a given length with its one end closed, produces a loud audible sound. Name the phenomenon responsible for it and explain the observation.
Resonance is the phenomenon that causes a loud audible sound when a vibrating tuning fork is held over an air column of a specific length with one end. The vibrating tuning fork causes forced...
In figure A, B, C and D are the four pendulums suspended from the same elastic string XY. The lengths of pendulum A and D are equal, while the length of pendulum B is shorter and of the pendulum C is longer. The pendulum A is set into vibrations.
(a) What is your observation about the vibrations of pendulum D?
(b) Give reason for your observation in part (a).
(c) What type of vibrations take place in pendulums B and C?
(d) Give reason for the answer in part (c)
Set the pendulum A into oscillation by moving it to one side, normal to its length. It is noticed that pendulum D begins vibrating with a tiny amplitude and eventually attains the same amplitude as...
Figure shows two tuning forks A and B of the same frequency mounted on two separate sound boxes with their open ends facing each other. The fork A is set into vibration. (a) Describe your observation. (b) State the principle illustrated by this experiment.
The vibrating tuning fork A produces forced vibrations in the air column of its soundbox. The vibrations in the soundbox have a significant amplitude due to the huge surface area of air in the...
Why is a loud sound is heard at resonance?
At resonance, the body vibrates with a significant amplitude, releasing a substantial quantity of energy into the medium. A loud sound is heard, which conveys greater energy to the ear.
State two differences between the forced and resonant vibrations
The forced vibrations have a limited amplitude.The resonant vibrations have a considerable amplitude.In forced vibrations body's vibrations are out of sync with the external periodic force.The...
Complete the following sentence:
Resonance is a special case of ______ vibrations, when the frequency of the driving force is _______ natural frequency of the driven body.
Resonance is a type of forced vibration in which the driving force's frequency is the same as the natural frequency of the driven body.
State the condition for the resonance to occur.
Resonance prerequisites: The phenomenon known as resonance happens when an applied force induces forced vibration in the body and the frequency of the applied force is exactly identical to the...
What is meant by resonance? Describe a simple experiment to illustrate the phenomenon of resonance and explain it.
When the frequency of an externally imposed periodic force on a body equals its natural frequency, the body begins to vibrate with greater amplitude. This phenomena is referred to as'resonance,' and...
State two differences between the natural and forced vibrations
(i) When a body is pushed from its equilibrium position and released, free vibrations occur, whereas forced vibrations are caused by an external periodic force of any frequency. (ii) In free...
On keeping the stem of a vibrating tuning fork on the surface of a table, a loud sound is heard. Give reason.
When the stem of a vibrating tuning fork is put on the top of a table, it causes forced vibrations in the tabletop. When the frequency of a periodic force applied to a body equals the inherent...
What are the forced vibrations? Give one example to illustrate your answer.
The vibrations of a body that occur under the influence of an external periodic force operating on it are known as forced vibrations. When a musician plays the guitar, he pushes the strings to...
Draw a sketch showing the displacement of a body executing damped vibrations, against time.
Below is a displacement time graph of damped vibrations. un
A tuning fork is set into vibrations in the air. Name the kind of vibrations it executes.
In the air, a tuning fork produces damped vibrations.
The diagram in figure shows the displacement-time graph of a vibrating body.
(i) Name the kind of vibrations.
(ii) Give one example of such vibration.
(iii) Why is the amplitude of vibrations gradually decreasing?
(iv) What happens to the vibrations of the body after some time?
(i) Vibrations that have been dampened(ii) Example: When a tuning fork is stroked on a rubber pad, it produces damped air vibrations.(iii) The frictional force reduces the amplitude of vibrations....
What are the damped vibrations? How do they differ from free vibrations? Give one example of each.
The periodic vibrations of a body with diminishing amplitude in the presence of a resistive force are known as damped vibrations. When a body is forced to vibrate in a medium, the amplitude of the...
How does the medium affect the amplitude of the natural vibrations of a body?
Because the surrounding medium resists motion, the energy of the vibrating body progressively declines, resulting in a steady decrease in the amplitude of vibration.
A blade, fixed at one end, is made to vibrate by pressing its other end and then releasing it. State one way in which the frequency of vibrations of the blade can be lowered.
The frequency of blade vibrations can be reduced by extending the blade's length or by placing a tiny weight on the blade's free end.
Explain why strings of different thickness are provided on a stringed instrument.
On a stringed instrument, variable thickness strings are used to generate different frequency sound waves. This is because a stretched string's inherent frequency of vibration is inversely...
The diagram below in Fig. shows three ways in which the string of an instrument can vibrate.
(a)Which of the diagram shows the principal note?
(b)Which vibration has the frequency four times that of the first?
(c) Which vibration is of longest wavelength?
(d)What is the ratio of the frequency of vibrations in the diagram (i) and (ii)?
(a) A diagram depicting the main note is (i) (b) A diagram with four times the frequency of the first is shown (iii) The diagram with the longest wavelength is shown in (c) (i) (d) The frequency of...
What adjustments would you make for tuning a stringed instrument for it to emit a note of a desired frequency?
We may get the required frequency by changing the tension. As a result, a stringed instrument has the ability to alter the tension of the string.
How does the frequency of sound given by a stretched string depend on its (a) length, (b) tension?
(a) String length: Sound frequency is inversely related to string length. (b) Tension: The square root of the tension in the string is exactly related to the frequency of sound.
State two ways of increasing the frequency of vibrations of a stretched string.
There are two methods for raising the frequency of a stretched string's vibrations (i) By raising the string's tension. (ii) By reducing the string's length.
State one way of increasing the frequency of a note produced by an air column
The frequency of the note generated in the air column can be enhanced by shortening the air column.
(a) Name one factor on which the frequency of sound emitted due to vibration in an air column depends.
(b) How does the frequency depend on the factor stated in part (a)?
(a) The length of an air column is affected by the frequency of sound released owing to vibration in the air column. (b) As the length of the air column grows longer, the frequency drops. As a...
State one condition for a body to execute the natural vibrations.
Because the existence of medium around the body provides some resistance, the amplitude of vibration diminishes with time and does not remain constant. As a result, a body's inherent vibrations can...
(a) Draw a graph between displacement and time for a body executing the natural vibrations
(b) Where can a body execute the natural vibrations?
The displacement time graph for free vibrations for a body performing free vibrations is presented below. When the oscillations of a body are placed into vibrations by any external force and then...
What is meant by the natural frequency of vibrations of a body? Name one factor on which it depends?
When any body capable of vibrating is set to vibrate freely at a frequency of f, the natural frequency of vibration of the body happens. The inherent frequency vibration of a body is determined by...
What do you understand by the natural vibrations of a body? Give one example.
The vibrations of a body in the absence of any external force are known as natural or free vibrations. Consider the following scenario: When we strike the keys of a piano, several strings are placed...
The figure below shows the distance-displacement graph of two waves A and B. Compare (i) the amplitude, (ii) the wavelength of the two waves.
The largest deviation from the mean position is called amplitude. The maximum displacement for A is 10 cm, and The maximum displacement for B is 5 cm. A1 / A2 = 10 / 5 = 2 / 1 = 2: 1 is the greatest...
On sending an ultrasonic wave from a ship towards the bottom of a sea, the time interval between sending the wave and receiving it back is found to be 1.5 s. If the velocity of the wave in seawater is 1400 m/s, find the depth of sea.
(velocity / time) / 2 = depth of the sea \(1400\times1.5\) / 2 = 1050 meters
A person standing at a distance x in front of a cliff fires a gun. Another person B standing behind the person A at a distance y from the cliff hears two sounds of the fired shots after 2s and 3s respectively. Calculate x and y (take speed of sound 320 m/s)
Two of the fired rounds are heard by person B; the first is straight from the gun, while the second is reflected from the cliff. Given a sound speed of 320 m/s The time it takes for sound to travel...
A person standing between two vertical cliffs produces the sound. Two successive echoes are heard at 4s and 6s. Calculate the distance between the cliffs. (Speed of sound in air = 320m/s)
The first cliff's distance from the guy, 2\(\times \)D1 = velocity\(\times \)time D1 = (320 \(\times \)4) / 2 D1 is equal to 640 metres. D2 = (320 \(\times \) 6) / 2 is the distance between the...
A pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fires a gun simultaneously. He hears an echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340m/s, find the distance between the cliff and the observer.
We know that, The pendulum vibrates 5 times each second. As a result, for 8 vibrations, the time is 8 / 5 seconds. similarly 2 D / time = Velocity 2 D / 1.6 = 340 This implies that...
A ship on the surface of water sends a signal and receives it back from the submarine inside water after 4s. Calculate the distance of the submarine from the ship. (The speed of sound in water is 1450 m/s).
We know that, \(2D=velocity\times time\) Therfore, \(D=\frac{1450\times 4}{2}\) D = 2.9 kilometres
A man standing 48 m away from a wall fires a gun. Calculate the time after which an echo is heard. (The speed of sound in air is 320m/s).
2 D / Time = Velocity 2D / velocity = time after which an echo is heard = \(\frac{2\times 48}{320}\) =0.3 seconds
A RADAR sends a signal to an aeroplane at a distance 300 km away, with a speed of m/s. After how much time is the signal received back after reflecting from the aeroplane?
Given RADAR's sound transmission speed is \(3\times {{10}^{8}}\)m/ s. The signal's transmission distance = 300 km = 300000 meters The signal travels twice, thus the distance is computed twice when...
A man standing 25 m away from a wall produces a sound and receives the reflected sound. (a) Calculate the time after which he receives the reflected sound if the speed of sound in air is 350 m/s. (b) Will the man be able to hear a distinct echo? Explain the answer.
(a) Velocity = Time / 2D so, time= \(\frac{2\times 25}{350}\) Hence, Time = 0.143 seconds (b) The reflected sound arrives at the guy 0.1 second after the initial sound, while the original sound...
What should be the minimum distance between the source and reflector in water so that echo is heard distinctly? (The speed of sound in water = 1400m/s)
We know that 2D / Time = Velocity 2 D / 0.1 = 1400 D\(=\frac{1400\times 0.1}{2}\) D = 70 metres
Calculate the minimum distance in the air required between the source of sound and the obstacle to hear an echo. Take the speed of sound in air = 350m/s
We are aware of this. 2D / 0.1 = Velocity D \(=\frac{350\times 0.1}{2}\) Hence, D = 17.5m
The wavelength of waves produced on the surface of water is 20cm. If the wave velocity is 24m/s, calculate (i) the number of waves produced in one second and (ii) the time in which one wave is produced.
(i)The frequency or number of waves produced per second = wavelength / velocity =\(\frac{24}{20}\times {{10}^{-2}}\) =120 (ii) Time it takes for one wave to form = 1 / frequency = 1/120 =...
To detect the obstacles in their path, bats produce:
(a) Infrasonic waves
(b) Ultrasonic waves
(c) Electromagnetic waves
(d) Radio waves
Bats generate (b) ultrasonic waves to identify impediments in their route
The minimum distance between the source and the reflector in air, so that an echo is heard is approximately:
(a) 10 m
(b) 17 m
(c) 34 m
(d) 50 m
In air, the minimum distance between the source and the reflector for an echo to be heard is around (b) 17 m.
State the use of echo in the medical field.
The echo technique using ultrasonic waves is used in medical science to image human organs such as the liver, gall bladder, uterus, and womb. Ultrasonography is the term for this procedure....
What is ‘SONAR’? State the principle on which it is based.
SONAR stands for sound navigation and ranging. Ultrasonic waves are released into the ocean from the ship in all directions. These waves are reflected back from the barrier, such as an iceberg or a...
Name the waves used for sound ranging. State one reason for their use. Why are the waves mentioned by you not audible to us?
Ultrasonic waves are utilized for sound range. The frequency of these ultrasonic waves exceeds 20,000 Hz, while the human ear's audibility range is 20 Hz to 20,000 Hz.
What is meant by sound ranging? Give one use of sound ranging.
Sound ranging is the process of using echo to identify barriers. Sound range is used by bats and dolphins to detect their prey.
How do bats avoid obstacles in their way, when in flight?
Bats can create and perceive ultra-high-frequency sounds up to roughly 100 kHz. Bats' sound is reflected back to them by a barrier in front of them as they fly. They can tell where the obstacles are...
State the use of echo by a bat, dolphin and fisherman.
Bats make noise, which is reflected back to them by an obstruction. They can locate the barrier by hearing the echo and fly around it securely without hitting with it. Dolphins identify their...
Explain how the speed of sound can be determined by the method of echo?
To hear an echo, the sound must travel from the source to the reflector and then back from the reflector to the source. If d is the distance between the source and the reflector, then 2d is the...
State two applications of echo.
The uses of echo are numerous. (i) Because dolphins can't see with their eyes, they utilize echolocation to find their way around. They can tell whether there is an item in front of them by...
A man is standing at a distance of 12m from a cliff. Will he be able to hear a clear echo of his sound? Give a reason for your answer.
The duration of time it takes to hear the echo is t = 2d / v t = (2 × 12) / 340 t = 24 / 340 < 0.1 seconds The man will not hear the echo because the feeling of a sound lasts around 0.1 second in...
What is meant by an echo? State two conditions necessary for an echo to be heard distinctly
The sound heard following reflection off a distant obstacle (such as a cliff, a hillside, a building wall, etc.) after the initial sound has stopped is termed an echo. There are two requirements...
What do you mean by reflection of sound? State one condition for the reflection of a sound wave. Name a device in which reflection of a sound wave is used.
The return of a sound wave in the same medium after impacting a surface such as a wall, metal sheet, or plywood is known as reflection of the sound wave. The sole need for a sound wave to be...
State two differences between the light and sound waves.
Difference between Waves of light and sound are Electromagnetic waves are light waves.Mechanical waves are sound waves.They have the ability to travel in a vacuum.For proliferation, they require a...
State two factors on which the speed of a wave travelling in a medium depends.
The elasticity and density of the medium through which sound travels determine its speed. In liquids, sound travels faster than in gases, and in solids, sound travels faster than in liquids. Sound...
A wave passes from one medium to another medium. Mention one property of the wave out of speed, frequency or wavelength (i) which changes, (ii) which does not change.
(i) The wavelength (or speed) of a wave varies when it travels from one medium to another. (ii) The frequency of a wave travelling in one media does not change as it travels through another medium.
Define the following terms in relation to a wave:
(a) amplitude
(b) frequency
(c) wavelength and
(d) wave velocity
(a)The amplitude of a wave is the distance between its resting position and its greatest movement. (b) Frequency is the number of waves travelling by a given location per second. (c) The wavelength...
What are mechanical waves?
Mechanical waves are waves that transmit energy through a material medium
To an astronaut in a space-ship, the earth appears:
(a) white
(b) red
(c) blue
(d) black
The world seems blue to an astronaut aboard a spaceship
In the white light of the sun, maximum scattering by the air molecules present in the earth’s atmosphere is for:
(a) red colour
(b) yellow colour
(c) green colour
(d) blue colour
The highest scattering by the air molecules present in the earth's atmosphere in the white light of the sun is for blue colour.
Give reason why the smoke from a fire looks white.
Because the size of the smoke particles is larger than the wavelength of the light, it looks white. White light is a combination of several wavelengths, yet they all scatter to the same amount...
The clouds are seen as white. Explain.
Dust particles are contained in the clouds, which are closer to the earth's surface. Clouds contain water droplets that are larger than the wavelengths of all seven colours of light. As a result,...
The sky at noon appears white. Give reason.
The sun is directly overhead at noon, thus light travels a shorter distance through the atmosphere to reach the ground. Only blue light is dispersed due to the short distance of light, while the...
Why does the sun appear red at sunrise and sunset?
At dawn and sunset, the sun's light must travel the greatest distance through the atmosphere to reach the observer. Because blue light with a short wavelength is lost owing to scattering, red light...
The colour of the sky, in the direction of the sun, is blue. Explain.
As light passes through the atmosphere, the air molecules in its passage disperse it in different ways. Because of its small wavelength, blue light scatters more than red light with a longer...
What characteristic property of light is responsible for the blue colour of the sky?
Because of its short wavelength, blue is the colour that scatters the most. The sky's blue colour is due to the scattering characteristic of light.
How would the sky appear when seem from the space (or moon) ? Give reason for your answer .
Because the moon has no atmosphere, there is no light scattering on its surface. As a result, no light reaches the eyes of an observer on the moon's surface save that which comes directly from the...
The danger signal is red. Why?
In visible light, red light has the longest wavelength. As a result, red-colored light is dispersed the least by air molecules in the environment. As a result, when compared to other colours, red...
Which colour of white light is scattered the least? Give reason.
The light with the longest wavelength is the least dispersed. As a result, red-colored light scatters the least.
A beam of blue, green and yellow light passes through the Earth’s atmosphere. Name the colour which is scattered (a) the least (b) the most
(a) Yellow light has the longest wavelength of the three radiations. As a result, it is the least dispersed. (b) Blue light has the shortest wavelength of the three radiations. As a result, it is...
When sunlight enters the earth’s atmosphere, a state which colour of light is scattered the most and which the least.
Because the intensity of dispersed light is inversely proportional to the wavelength's fourth power. As a result, violet is the most widely dispersed colour, whereas red is the least.
How does the intensity of scattered light depend on the wavelength of incident light? State conditions when this dependence holds.
The fourth power of the wavelength is discovered to be inversely related to the intensity of scattered light. When the size of the air molecules is less than the wavelength of incoming light, this...
What is meant by scattering of light?
As soon as the white light from the sun enters the earth's atmosphere, it gets dispersed or spread out in all directions by dust particles and air molecules. The dispersion of light is the name for...
The wavelength of X-rays is 0.01Calculate its frequency.
Given, wavelength is 0.01\(\overset{\circ }{\mathop{A}}\,\) Rays speed=\(3\times {{10}^{8}}\) Light speed = frequency × wavelength \(c=\frac{\lambda }{v}\) Therefore, Frequency= \(3\times...
An electromagnetic wave has a frequency of 500MHz and a wavelength of 60cm.
(a) Calculate the velocity of the wave.
(b) Name the medium through which it is travelling.
(a)An electromagnetic wave has a frequency of 500MHz so, Frequency = 500 MHz Wavelength = 60 cm Wave velocity = frequency x wavelength Therefore, Wave velocity is \(3\times {{10}^{8}}\) (b) An...
A radiation P is focused by a proper device on the bulb of a thermometer. Mercury in the thermometer shows a rapid increase. The radiation P is
(a) infrared radiation
(b) visible light
(c) ultraviolet radiation
(d) X-rays
P stands for infrared radiation.
The source of ultraviolet light is:
(a) electric bulb
(b) red hot iron ball
(c) sodium vapour lamp
(d) carbon arc-lamp
Carbon arc-lamps are the source of UV light.
The most energetic electromagnetic radiations are:
(a) microwaves
(b) ultraviolet waves
(c) X- rays
(d) gamma rays
Gamma rays are the most energetic electromagnetic radiations.
Give a reason for the following:
(i) Infrared radiations are used for photography in fog
(ii) Infrared radiations are used for signals during the war.
(iii)The photographic darkrooms are provided with infrared lamps.
(iv)salt prism is used instead of a glass prism to obtain the infrared spectrum.
(v)A quartz prism is required for obtaining the spectrum of the ultraviolet light.
(vi)Ultraviolet bulbs have a quartz envelope instead of glass.
(i)Infrared radiations are employed for fog photography because they are less dispersed and can penetrate the fog effectively. (ii)Because infrared radiation is not visible and does not absorb well...
State one harmful effect each of the (a) ultraviolet and (b) infrared radiations.
(a) If the human body is exposed to ultraviolet light for an extended period of time, it might create health problems such as skin cancer. (b) Skin burns are caused by infrared radiation.
Name the radiations which are absorbed by the greenhouse gases in the earth’s atmosphere.
Water vapour, carbon dioxide, methane, and ozone are the major greenhouse gases found in the earth's atmosphere. The greenhouse gases in the earth's atmosphere absorb infrared energy.
Name the material of prism required for obtaining the spectrum of (a) ultraviolet light, (b) infrared radiations
a) To obtain the UV light spectrum, you'll need a quartz prism. (b) By passing radiations through a rock salt prism, infrared radiations can be obtained.
Give two properties of infrared radiations which differ from the visible light.
Infrared radiation has two distinct qualities from visible light. (a) They absorb through glass, but not through rock salt. (b) A thermopile or a darkened bulb thermometer is used to identify them...
Mention three properties of infrared radiations similar to the visible light.
In vacuum, infrared radiations travel in straight lines like light, at a speed of \(3\times {{10}^{8}}\) m/s. (b) They follow the reflection and refraction laws. (c) Electric and magnetic fields...
Give two properties of ultraviolet radiations which differ from the visible light.
UV rays have two characteristics that distinguish them from visible light. (a) Although ultraviolet rays can penetrate through quartz, they are absorbed by the glass. (b) They are commonly dispersed...
Name three properties of ultraviolet radiations which are similar to the visible light.
(a) In air or vacuum, ultraviolet radiation travels in a straight line with a speed of \(3\times {{10}^{8}}\) m\s. (b) They follow the reflection and refraction laws. (c) Because they are chemically...
What are ultraviolet radiations? How are they detected? State one use of these radiations
Ultraviolet radiations are electromagnetic waves with wavelengths between 100\(\overset{\circ }{\mathop{A}}\,\) to 4000\(\overset{\circ }{\mathop{A}}\,\) Detection: If a silver chloride solution is...
What are infra-red radiations? How are they detected? State one use of these radiations.
The electromagnetic waves of wavelength in the range of 8000\(\overset{\circ }{\mathop{A}}\,\) to 10000000\(\overset{\circ }{\mathop{A}}\,\) are known as infrared radiations Detection: When a...
Name two sources, each of infrared radiations and ultraviolet radiations.
Infrared radiations are emitted by all red hot bodies, such as a heated iron ball, flame, or fire. Ultraviolet radiation is produced by electric arcs and sparks.
Two waves A and B have wavelength of 0.01 and 9000respectively
Name the two waves.
(b) Compare the speeds of these waves when they travel in a vacuum.
(a) Gamma rays and infrared radiations (Wave A and B). (b) In vacuum, all electromagnetic waves travel at the speed of light. In a vacuum, the ratio of these waves' velocity is 1: 1.
(a) Gamma rays have the lowest wavelength
(b) Infrared rays are used for taking photographs in the dark
(c) Gamma rays are the waves produced by the changes in the nucleus of an atom
(d) X-rays have wavelength nearly 0.1 nm
(a)The wavelength of gamma rays is the shortest. (b) Infrared photons are employed to take photos in low light. (c) Gamma rays are the waves created by changes in an atom's nucleus. (d) X-rays have...
Give one use each of (a) microwaves, (b) ultraviolet radiations, (c) infrared radiations, and (d) gamma rays.
(a) Radar communication uses microwaves. (b) Ultraviolet rays are employed in the production of vitamin D in plants and animals' diet. (c) Infrared radiation is utilised to control televisions and...
Name two electromagnetic waves of wavelength smaller than that of violet light. State one use of each
X-rays and ultraviolet radiations are electromagnetic waves with shorter wavelengths than violet light. UV rays have a wavelength of 100 \(\overset{\circ }{\mathop{A}}\,\) to 4000\(\overset{\circ...
Name the radiations of wa velength just (a) longer than ,m (b) shorter than m
(a)Infrared radiation has a wavelength of more than \(8\times {{10}^{-7}}\) m. (b)Ultraviolet radiation has a wavelength of less than \(4\times {{10}^{-7}}\)m
State the approximate range of wavelength associated with (a) the ultraviolet rays, (b) the visible light, and (c) infrared rays.
(a)Ultraviolet rays have a wide range of wavelengths from 100 \(\overset{\circ }{\mathop{A}}\,\) to 4000\(\overset{\circ }{\mathop{A}}\,\) (b) Visible rays have a wide range of wavelengths from 4000...
Name the radiation which can be detected by (a) a thermopile (b) a solution of silver chloride
(a)The thermopile can detect infrared radiation. (b)Silver chloride can detect ultraviolet radiations because it turns dark in their presence.
What do you understand by the invisible spectrum?
The invisible spectrum is the portion of the spectrum between the red and violet extremes to which our eyes do not respond.
Name the region beyond (i) the red end and (ii) the violet end, of the spectrum.
(i)Infrared light is found beyond the red end of the spectrum. (ii)The ultraviolet part of the spectrum is located beyond the violet end of the spectrum.
Give the range of wavelength of the electromagnetic waves visible to us.
The visible electromagnetic waves have a wavelength of 4000\(\overset{\circ }{\mathop{A}}\,\) to 8000\(\overset{\circ }{\mathop{A}}\,\)
Name three radiations and their wavelength range which are invisible and beyond the violet end of the visible spectrum.
Beyond the violet end of the visible spectrum, there are three rays that are unseen. (i) Gamma rays (ii) X-rays (iii) Ultraviolet rays There wavelengths are: (i) Gamma rays – less than 0.01 nm (ii)...
State the name and the range of wavelength of the invisible electromagnetic waves beyond the red end of the visible spectrum.
Infrared radiations are electromagnetic waves that extend beyond the visible light spectrum's red extreme and provide a substantial heating impact. The wavelength range is 8000\(\overset{\circ...
(a) Name the high energetic invisible electromagnetic wave which helps in the study of the structure of crystals.
(b) State one more use of the wave named in part (a).
(a)In the study of crystals, X-rays are used. (b)It can also be used to diagnose fractures in bones and teeth.
A wave has wavelength 50
(a)Name the wave.
(b) State its speed in vacuum
(c) State its one use.
(a) X rays have a wavelength of 50\(\overset{\circ }{\mathop{A}}\,\) (b) In vacuum, the speed of an electromagnetic wave is \(3\times {{10}^{8}}\) m/s. (c) Because they are stopped by bones, they...
A wave has a wavelength of nm (a) Name the wave (b) State it’s one property different from light.
(a)The wavelength of gamma rays is \({{10}^{-3}}\) nm. (b) Gamma rays have a powerful penetrating ability.
(a) Arrange the following radiations in the order of their increasing wavelength:X-rays, infrared rays, radio waves, gamma rays and microwaves
(b) Name the radiation which is used for satellite communication?
(a) Radiations are arranged in increasing wavelength order. (i) Gamma rays (ii) X- rays (iii) Infrared rays (iv) Microwaves (v) Radio waves (b) Satellite communication is carried out using...
(a) Give a list of at least five radiations, in the order of their increasing wavelength, which make up the complete electromagnetic spectrum.
(b) Name the radiation mentioned by you in part (a) which has the highest penetrating power.
The electromagnetic spectrum is organised in increasing order of wavelength. (i)gamma rays (ii)X – rays (iii)Ultraviolet rays (iv)Light that can be seen (v)Infrared radiations (b) Gamma rays are the...
The frequency range of visible light is from Hz to Hz. Calculate its wavelength range. Take speed of light = m/s
Given, \(c=3\times {{10}^{8}}\) m/s is the speed of light. \(3.75\times {{10}^{14}}\)Hz to \(7.5\times {{10}^{14}}\) Hz is the frequency range. We know that, Frequency x wavelength = light speed If...
Where should an object be placed in front of a convex lens of focal length 0.12 m to obtain a real image of size three times the size of the object, on the screen?
Solution: According to the question, Focal length of the given convex lens is f = + 0.12 m Magnification is m = -3 (real image) For a lens, expression of magnification is m = v / u upon substituting...
The focal length of a convex lens is 25 cm. At what distance from the optical centre of the lens an object be placed to obtain a virtual image of twice the size?
Solution: According to the question, Focal length is f = +25 cm Image is virtual and magnified, with magnification (m) = +2 For a lens, expression for the magnification is m = v / u Or, +2 = v / u...
A concave lens forms the image of an object kept at a distance 20 cm in front of it, at a distance 10 cm on the side of the object.
(a) What is the nature of the image? (b) Find the focal length of the lens. Solution: According to the question, Object distance is u = -20 cm Image distance is v = – 10 cm (a) Because the image is...
(a) At what position a candle of length 3 cm be placed in front of a convex lens so that its image of length 6 cm be obtained on a screen placed at distance 30 cm behind the lens?
(b) What is the focal length of the lens in part (a)? Solution: According to the question, Height of a candle is 3 cm Height of the image is 6 cm Image distance is 30 cm (a) Expression for the...
The maximum magnifying power of a convex lens of focal length 5 cm can be:
(a) 25 (b) 10 (c) 1 (d) 6 Solution: According to the question, Focal length of convex lens is f = +5 cm Expression for the magnifying power of the convex lens (simple microscope) is M = 1 + D / f...
A magnifying glass forms:
(a) A real and diminished image (b) A real and magnified image (c) A virtual and magnified image (d) A virtual and diminished image Solution: The correct option is (c). Therefore, a magnifying glass...
How will you differentiate between a convex and a concave lens by looking at
(i) a distant object and (ii) a printed page? Solution: (i) If the inverted image of a distant object is seen through the lens, the lens is convex; if the upright image is visible, the lens is...
Describe how you would determine the focal length of a converging lens, using a plane mirror and one pin. Draw a ray diagram to illustrate your answer.
Solution: A vertical stand, a plane mirror, a lens, and a pin are required to determine the focal length using a plane mirror. Place the lens L on a plane mirror MM' horizontally. Arrange the pin P...
The diagram below shows the experimental set up for the determination of the focal length of a lens using a plane mirror.
(i)Draw two rays from the point O of the object pin to show the formation of image I at O itself. (ii)What is the size of the image I? (iii)State two more characteristics of the image I. (iv)Name...
Describe in brief how would you determine the approximate focal length of a convex lens.
Solution: A convex lens' approximate focal length can be calculated using the premise that a beam of parallel rays incident from a distant object converges in the lens' focal plane. The 0 centimetre...
State two applications each of a convex lens and concave lens.
Solution: Some of the applications of a convex lens are (i) A telescope, camera, slide projector, or other device's objective lens is a convex lens that creates a real and inverted image of the...
Write an expression for the magnifying power of a simple microscope. How can it be increased?
Solution: Expression for the magnifying power of the microscope is as follows - M = 1 + D / f, where M denotes the magnifying power Where f denotes the lens' focal length and D denotes the shortest...
Where is the object placed in reference to the principal focus of a magnifying glass, so as to see its enlarged image? Where is the image obtained?
Solution: The item is positioned between the lens and the point of primary focus. The image is formed in the distance between the lens and the primary focus.
Draw a neat labelled ray diagram to locate the image formed by a magnifying glass. State three characteristics of the image.
Solution: When the object is situated between focal length and the optical centre of a convex lens, the image of the object will form on the same side of the lens. In the diagram below, AB...
What is magnifying glass? State its two uses.
Solution: A convex lens with a short focal length is known as a magnifying glass. For practical use, it is fitted in a lens holder. It's used to see and read little characters and figures...
A ray of light incident on a lens parallel to its principal axis, after refraction passes through or appears to come from:
(a) Its first focus(b) Its optical entre(c) Its second focus(d)The centre of curvature of its second surface Solution: The ray of light after refraction passes through or appears to come from its...
A ray of light after refraction through a lens emerges parallel to the principal axis of the lens. The incident ray either passes through :
(a) its optical centre(b) its first focus(c) its second focus (d) it’s centre of curvature of the first surface Solution: the correct option is (b). The incident ray passes through its first...
The lens of power + 1.0 D is :
(a) convex of focal length 1.0 cm (b) convex of focal length 1.0 m (c) concave of focal length 1.0 cm (d) concave of focal length 1.0 m Solution: The correct option is (d). According to the...
On reducing the focal length of a lens, its power:
(a) Decreases (b) Increases (c) Does not change (d) First increases then decreases. Solution: The correct option is (b). On reducing the focal length of a lens, the power of the...
The correct lens formula is
(a) 1 / u + 1 / v = 1 / f (b) 1 / u – 1 / v = 1 / f (c) 1 / v – 1 / u = 1 / f (d) f = (u + v) / uv Solution: The correct option is (c). Expression for the lens formula is - 1 / v – 1 / u = 1 / f...
If the magnification produced by a lens is – 0.5, the correct statement is :
(a) The lens is concave (b) The image is virtual (c) The image is magnified (d) The images are real and diminished formed by a convex Solution: The correct option is (d). The image is real and...
Which lens has more power: a thick lens or a thin lens?
Solution: The power of a thick lens is more than a thin one because a thick lens has greater curvature or lesser focal length as compared to a thin lens.
The power of a lens is negative. State whether it is convex or concave?
Solution: We know that the expression for power of a lens is - P = 1/f, where f is the focal length of the lens Since the focal length of a convex lens is positive and it is negative for a concave...
How is the sign (+ or -) of power of a lens related to its divergent or convergent action?
Solution: The direction in which a light ray is deviated by the lens determines the power sign. It's possible that the power is positive or negative. The power of a lens is positive if it deviates a...
How does the power of a lens change if its focal length is doubled?
Solution: Power pf a lens is inversely proportional to its focal length in the following manner - P = 1/f where f is the focal length. So according to the expression, when the focal length is...
How is the power of a lens related to its focal length?
Solution: The ability of a lens to concentrate incoming rays is known as the power. Power of a lens is related to its focal length in the following manner - P = 1 / f Or, Power of lens (in D) = 1 /...
Define the term power of a lens. In what unit is it expressed?
Solution: The ability of a lens to concentrate light rays falling on it is known as power of the lens. Expression for the Power of lens is as follows : P = 1 / f where f is the focal length. Dioptre...
What information about the nature of the image (i) real or virtual, (ii) erect or inverted, do you get from the sign of magnification + or -?
Solution: (i) A positive magnification denotes that the image generated is virtual. Whereas a negative sign denotes that the image formed is genuine. (ii) A positive magnification denotes that the...
What do you understand by the term magnification? Write expression for it for a lens, explaining the meaning of the symbols used.
Solution: The ratio of the size of the image to the size of the object is known as the magnification. The expression for magnification is m = -v / u where v is the image distance and u is the object...
Write the lens formula explaining the meaning of the symbols used.
Solution: According to the Lens formula, we have - 1 / v – 1 / u = 1 / f where ‘u' is the object's distance from the lens' optical centre The image's distance from the optical center is v, and the...
The focal length of a lens is (i) positive, (ii) negative.
In each case, state the kind of lens. Solution: (i) If a lens' focal length is positive, the lens is said to be convex.(ii) A lens is called a concave lens if its focal length is negative.
State the sign convention to measure the distances for a lens.
Solution: (a) The primary axis is the axis along which distances are measured. These distances are measured from the lens's optical centre.(b) Positive distances are those measured in the same...
A concave lens forms the image of an object which is:
(a) Virtual, inverted and diminished (b) Virtual, upright and diminished (c) Virtual, inverted and enlarged (d) Virtual, upright and enlarged Solution: Correct option is (b). A concave lens forms...
For the object placed between the optical centre and focus of a convex lens, the image is:
(a) Real and enlarged (b) Real and diminished (c) Virtual and enlarged (d) Virtual and diminished. Solution: The correct option is (c). The image is virtual and enlarged.
For an object placed at a distance 20 cm in front of a convex lens, the image is at a distance 20 cm behind the lens. The focal length of the convex lens is:
(a) 20 cm (b) 10 cm (c) 15 cm (d) 40 cm Solution: The correct option is (b) 10 cm, the focal length of a convex lens is 10 cm. Formula Used - 1/f = 1/v + 1/u According to the question, v = 20cm and...
State whether the following statements are ‘true’ or ‘false’ by writing T/F against them.
(d)A ray of light incident at the optical centre of the lens, passes undeviated after refraction (e)A concave lens forms a magnified or diminished image depending on the distance of...
State whether the following statements are ‘true’ or ‘false’ by writing T/F against them.
(a)A convex lens has a divergent action and a concave lens has a convergent action. (b)A concave lens, if kept at a proper distance from an object, can form its real image (c)A ray of light incident...
In Fig. (a) and (b), F1 and F2 are the two foci of the thin lenses and AB is the incident ray. Complete the diagram to show the path of the ray AB after refraction through the lens.
Solution: (a) (b)
Complete the following sentences :
(a)If half part of a convex lens is covered, the focal length __________ change, but the intensity of image _________. (b)A convex lens is placed in water. Its focal length will ________. (c)The...
In Fig. (a) and (b), F1 and F2 are the positions of the two foci of the thin lenses. Draw the path taken by the light ray AB after it emerges from each lens.
Solution: (a) (b)
The diagram below shows a lens as a combination of a glass block and two prisms.
(i)Name the lens formed by the combination. (ii)What is the line XX’ called? (iii)Complete the ray diagram and show the path of the incident ray AB after passing through the lens. (iv)The final...
A parallel oblique beam of light falls on a
(i) convex lens, (ii) concave lens. Draw a diagram in each case to show the refraction of light through the lens. Solution: (i) A convex lens refracts an oblique parallel beam. (ii) A concave lens...
State the condition for each of the following :
(i) a lens has both its focal lengths equal. (ii) a ray passes undeviated through the lens. Solution: (i) If the focal lengths on both sides of the lens are equal, medium is the...
What do you mean by the focal plane of a lens?
Solution: The focal plane of a lens is a plane parallel to the primary axis that passes across the focus.
Define the term focal length of a lens.
Solution: The focal length of a lens is the distance of focus point from the optical centre of the lens.
A beam of light incident on a thin concave lens parallel to its principal axis diverges and appears to come from a point F on the principal axis. Name the point F. Draw a ray diagram to show it.
Solution: This point F appears to come from a second focus
A beam of light incident on a convex lens parallel to its principal axis converges at a point F on the principal axis. Name the point F. Draw a ray diagram to show it.
Solution: This point F is known as the second focus.
A ray of light, after refraction through a concave lens emerges parallel to the principal axis.
(a) Draw a ray diagram to show the incident ray and its corresponding emergent ray. (b) The incident ray when produced meets the principal axis at a point F. Name the point F. Solution: (a) (b) When...
Draw a diagram to represent the second focus of a convex lens.
Solution:
Draw a diagram to represent the second focus of a concave lens.
Solution:
Define the term principal foci of a concave lens and show them with the help of proper diagrams.
Solution: From either side, a light ray can travel through a lens. As a result, a lens has two primary foci.The first focal point of a concave lens is a point F1 on the principal axis of the lens...
Define the term principal foci of a convex lens and illustrate your answer with the aid of proper diagrams.
Solution: From either side, a light ray can travel through a lens. As a result, a lens has two primary foci, one on each side.The first focal point of a convex lens is a point F1 on the primary axis...
State the condition when a lens is called an equiconvex or equi-concave.
Solution: The lens is called equiconvex or equi-concave if the radius of curvature of both surfaces are equal.
A ray of light incident at a point on the principal axis of a convex lens passes undeviated through the lens.
(a) What special name is given to this point on the principal axis? (b) Draw a labelled diagram to support the answer in part(a). Solution: (a) Optical centre is the name of this point on the...
Explain the optical centre of a lens with the help of proper diagram(s).
Solution: The optical centre is a position on the lens's primary axis where a ray of light travelling through it emerges parallel to its incidence direction. In the diagram below, the letter O...
Define the term principal axis of a lens.
Solution: A line connecting the centres of curvature of the two surfaces of the lens is known as the principal axis.
How does the action of the convex lens differ from that of a concave lens on a parallel beam of light incident on them? Draw diagrams to illustrate your answer.
Solution: When a parallel light beam strikes a convex lens, the prism in the upper portion bends the incident ray downwards. Similarly, the prism in the bottom section bends it upwards. The ray...
Show by a diagram the refraction of two light rays incident parallel to the principal axis on a concave lens by treating it as a combination of a glass slab and two triangular glass prisms.
Solution: The concave lens, which has two glass prisms and one glass slab, is shown above. One glass prism is located above the glass slab, while the other is located below it.
Show by a diagram the refraction of two light rays incident parallel to the principal axis on a convex lens by treating it as a combination of a glass slab and two triangular glass prisms.
Solution: The convex lens, which has two glass prisms and one glass slab, is depicted in the diagram above. One glass prism is positioned above the glass slab, while the other is positioned below...
Out of the two lenses, one concave and the other convex, state which one will show the divergent action on a light beam. Draw diagram to illustrate your answer.
Solution: Concave lens are known to show the divergent action on a light beam. The diagram below shows this behaviour of concave lens -
Which lens is converging:
(i) an equiconcave lens or an equiconvex lens? (ii) a concavo-convex lens or a convexo-concave lens? Solution: (i) A converging equiconvex lens(ii) A converging lens is a...
State difference between a convex and a concave lens in their
(a) appearance, and (b) action on the incident light. Solution: Convex Lens : (i) It is thick in the center and thin on the outside.(ii) The incident rays are converged towards the primary...