Science

We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

Answer- The object's distance from the mirror's pole ranges from 0 to 15 cm. The image's nature is virtual, upright, and larger than the thing.

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A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

Answer- Because the image is actual and the same size, it should be positioned at 2F. The image of the needle is assumed to be formed at a distance of 50 cm from the convex lens. As a result, the...

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In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate

Solution: The correct response is (b) lead acetate. Explanation: Because we need a compound that contains lead in order to obtain lead iodide, ammonium nitrate and potassium sulphate are ruled out....

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Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only
(b) (ii) only
(c) (iv) only
(d) (ii) and (iv)

Solution: Answer is option d) The elements ammonium and barium are being displaced from their respective salts, according to the data. As a result, we have a double displacement reaction. Because of...

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Which among the following statement(s) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to
(i) the formation of silver by decomposition of silver chloride
(ii) sublimation of silver chloride
(iii) decomposition of chlorine gas from silver chloride
(iv) oxidation of silver chloride
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iv) only

Solution: Answer is option a) Silver halides, particularly silver chloride, decompose in the presence of sunlight, resulting in the formation of silver metal and a halogen gas (silver) (chlorine or...

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Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by the liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(i) It is an endothermic reaction
(ii) It is an exothermic reaction
(iii) The pH of the resulting solution will be more than seven
(iv) The pH of the resulting solution will be less than seven
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)

Solution: The answer is (b) (ii) and (iii) In the presence of vigorous water reaction, solid calcium oxide transforms into calcium hydroxide, which is accompanied by the production of heat. This...

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Which among the following is(are) double displacement reaction(s)?
(i) Pb + CuCl2 → PbCl2 + Cu
(ii) Na2 SO4 + BaCl2 → BaSO4 + 2NaCl
(iii) C + O2 → CO2
(iv) CH4 + 2O2 → CO2 + 2H2O
(a) (i) and (iv)
(b) (ii) only
(c) (i) and (ii)
(d) (iii) and (iv)

Solution: The answer is (b) (ii) only Sodium and barium are both displaced from their respective salts in this reaction, which is referred to as a double displacement reaction.

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A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?
(a) KMnO4 is an oxidising agent, it oxidises FeSO4
(b) FeSO4 acts as an oxidising agent and oxidises KMnO4
(c) The colour disappears due to dilution; no reaction is involved
(d) KMnO4 is an unstable compound and decomposes in the presence of FeSO4 to a colourless compound.

Solution: Answer is (a) KMnO4 is an oxidising agent, it oxidises FeSO4 Potassium permanganate (KMnO4) is used as an oxidising agent during this reaction. This is due to the presence of KMnO4, which...

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Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas, in the case of beaker C, the temperature of the solution falls. Which one of the following statements(s) is(are) correct?
(i) In beakers A and B, the exothermic process has occurred.
(ii) In beakers A and B, the endothermic process has occurred.
(iii) In beaker C exothermic process has occurred.
(iv) In beaker C endothermic process has occurred.
(a) (i) only
(b) (ii) only
(c) (i) and (iv)
(d) (ii) and (iii)

Answer: Answer is (c) (i) and (iv) Exothermic processes result in the release of enormous amounts of heat – as a result, when water reacts with quick lime and when acid reacts with water, heat...

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Which of the following are exothermic processes?
(i) The reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)

Answer: Option a) Exothermic processes result in the release of enormous amounts of heat – as a result when water reacts with quick lime and when an acid reacts with water, heat energy is...

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Which of the following statements about the given reaction are correct? 3Fe(s) + 4H2O(g) → Fe3O4 (s) + 4H2 (g)
1. Iron metal is getting oxidised
2. Water is getting reduced
3. Water is acting as a reducing agent
4. Water is acting as an oxidising agent
(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)

Answer: Option c) In this reaction, oxygen reacts with water to form oxidised water. Because oxygen is being removed from water, the water's oxygen content is being reduced. Water is a source of...

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The following reaction is an example of a:4NH3 (g) + 5O2 (g) → 4NO(g) + 6H2O(g)
(i) displacement reaction
(ii) combination reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (iii) and (iv)

Solution: Answer is (c)  (i) and (iii) The reaction described here is a combination of displacement and redox reactions. The displacement reaction occurs when oxygen displaces hydrogen in ammonia,...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H_2SO_4
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.

Answer: (c) $C_2 H_5 OH ( aq )+ CH_3 COOH (l) \longrightarrow CH_3 COO C_2 H_5( aq )+ H_2 O ( t )$It is a neutralisation reaction and double displacement reaction.(d) $C_{2} H_{4}( g )+3 O_{2}(g)...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.

Answer: (a) $N {2}( g )+3 H {2}( g )=\frac{\text { catalyst }}{773 K } 2 NH {2}( g )$ It is a combination reaction. (b) $NaOH ( aq )+ CH _{3} COOH ( aq ) \longrightarrow CH_3 COONa ( aq )+ H_2 O...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.

Answer: c) Aqueous potassium iodide solution is passed through a chlorine gas stream, resulting in the formation of potassium chloride solution and solid iodine.This is a reaction with a single...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.

Answer: a) Iron (III) oxide reacts with aluminium to form molten iron and aluminium oxide in the first step of the Thermit reaction. This is a reaction with a single displacement. Fe2O3 + 2Al →...

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During the reaction of some metals with dilute hydrochloric acid, the following observations were made.
(a) Silver metal does not show any change
(b) The temperature of the reaction mixture rises when aluminum (Al) is added.

Answer: a) Because silver is a member of the low reactive series of metals, there will be no reaction between it and dilute hydrogen chloride. b) Due to the fact that it is an exothermic reaction,...

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During the reaction of some metals with dilute hydrochloric acid, the following observations were made.
(c) The reaction of sodium metal is found to be highly explosive
d) Some bubbles of gas are seen when lead (Pb) is reacted with the acid.

Answer: c) Sodium is a highly reactive metal, and when it reacts with atmospheric oxygen, it produces an exothermic reaction, which raises the temperature of the surrounding environment. d) Hydrogen...

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A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution that turns red litmus blue. Identify X and also write the chemical reactions involved.

Answer: Calcium oxide is the chemical compound X. CaO is a compound that is widely used in the cement industry. Water treatment of CaO results in the formation of Ca(OH)2, which is alkaline in...

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Write a balanced chemical equation for each of the following reactions and also classify them.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulfide gas reacts with oxygen gas to form solid sulfur and liquid water.

Answer: (c) Fe2O3 + 3CO + 2Fe + 3CO2 This is a redox reaction. (d) 2 H2S+O2 → 2 s + 2 H2O This is a replacement reaction.

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Write a balanced chemical equation for each of the following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.

Answer: (a) Pb(CH3COO)2 + 2HCI – PbCl2 + CH3COOH This is a Double Displacement reaction. (b) 2Na + 2C2H5OH + 2C2H5ONa+ H2 This is a Displacement reaction.

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A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by the emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is dissolved in water.

Solution: a) It is formed when magnesium ribbon is burned in oxygen with the emission of light and heat energy that magnesium oxide is formed.X is a compound with the chemical formula MgO. After...

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A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. (a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved. (b) Name the black substance formed and give its chemical formula.

Solution: A reaction between silver and H2S in the atmosphere results in the formation of Silver Sulphide, which is a dark brown compound with a sulfuric acid smell. Corrosion is the term used to...

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On heating blue colored powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X are formed
(c) Identify the type of reaction.
(d) What could be the pH range of the aqueous solution of the gas X?

Answer: c) Thermal decomposition is the reaction that is taking place. d) Due to the fact that NO2 dissolves in water and forms an acidic solution, pH is less than 7. (pH range below 7).

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On adding a drop of barium chloride solution to an aqueous solution of sodium sulfite, a white precipitate is obtained.
(a) Write a balanced chemical equation of the reaction involved
(b) What other name can be given to this precipitation reaction?

Solution: a)The reaction of a drop of Barium Chloride solution with one drop of sodium sulphite solution results in the formation of barium sulphite, a white precipitate of barium sulphite....

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Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit, another set of three bulbs of the same wattage are connected in parallel to the same source.
(a) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(b) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.

Answer: a) In a series configuration, the resistance of the bulbs is three times greater than the resistance of a single bulb. As a result, when compared to the current in each bulb in the parallel...

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B1 , B2, and B3 are three identical bulbs connected as shown in Figure 12.8. When all the three bulbs glow, a current of 3A is recorded by ammeter A.
What happens to the glow of the other two bulbs when the bulb B1 gets fused?
What happens to the reading of A1 , A2 , A3 and A when the bulb B2 gets fused?

Solution: In a parallel circuit, the potential difference does not become divided. As a result, when bulb one is fused, the glowing of the other bulbs will not be affected. 3 Amperes are being...

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A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 Ω when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if the resistance of 10 Ω is connected in parallel with this series combination, what change (if any) in current flowing through 5 Ω conductor and potential difference across the lamp will take place? Give reason.

Solution: Given: I= 1 A, V= 5 V 1) Let R be the resistance of the electric lamp. In series total resistance = 5 + R I = v/r 1 =  10/5+R R = 5 ohm 2) V across Lamp + conductor = 10 V V acoess Lamp =...

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Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 Ω in series with a combination of two resistors (4 Ω each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2 Ω resistor be the same as that across the parallel combination of 4Ω resistors? Give reason.

Solution: The circuit diagram is: The following equation can be used to calculate the total resistance of a parallel combination of 40 resistors: $\frac{1}{R}=\frac{1}{4}+\frac{1}{4}=\frac{1}{2}$$R...

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Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have
(a) same current flowing through them when connected in parallel
(b) same current flowing through them when connected in series
(c) the same potential difference across them when connected in series
(d) different p

Solution: The answer is (b) same current flowing through them when connected in series When using a series combination, the current is not divided into branches because the resistor receives a...

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In an electrical circuit, three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?
(a) The brightness of all the bulbs will be the same
(b) The brightness of bulb A will be the maximum
(c) The brightness of bulb B will be more than that of A
(d) The brightness of bulb C will be less than that of B

Solution: Answer is (c) Brightness of bulb B will be more than that of A Due to the fact that the bulbs are connected in parallel, their combined resistance will be less than the arithmetic sum of...

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A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R1, R2 and R3 respectively (Figure.12.5). Which of the following is true?
(a) R1 = R2 = R3
(b) R1 > R2 > R3
(c) R3 > R2 > R1
(d) R2 > R3 > R1

Solution: The answer is (c) R3 > R2 > R1 Resistance is inversely proportional to the amount of current flowing through it. Because the highest resistance will result in the least amount of current...

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Describe the activity that shows that a current-carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does Fleming’s left-hand rule help us to find the direction of the force acting on the current-carrying conductor?

Answer: Take a small aluminium rod (AB) and bend it in half (of about 5 cm). As shown in Fig. 1, you can suspend it horizontally from a stand by using two connecting wires. A strong horseshoe magnet...

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Explain with the help of a labeled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current-carrying coil has n turns the field produced at any point is n times as large as that produced by a single turn?

Answer: Even in a current-carrying loop, the right-hand thumb rule is observed and followed. This demonstrates that magnetic field lines are present all around the conducting wire. However, because...

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With the help of a labeled circuit diagram illustrating the pattern of field lines of the magnetic field around a current-carrying straight long conducting wire. How is the right-hand thumb rule useful to find the direction of the magnetic field associated with a current-carrying conductor?

Answer: A straight conductor carrying current is held in the right hand with the thumb pointing in the direction of the current, according to the right-hand thumb rule. The fingers of the right hand...

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Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current-carrying loop is brought near it. Describe some salient features of magnetic lines of field concept.

Answer:Current carrying loops act as bar magnets with associated lines of the field, which are represented by the arrows. As a result, the existing earth's magnetic field is altered, resulting in a...

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Meena draws magnetic field lines of the field close to the axis of a current-carrying circular loop. As she moves away from the centre of the circular loop she observes that the lines keep on diverging. How will you explain her observation?

Answer: The magnetic field strength decreases as the distance between the two points decreases. It is indicated by a decrease in the degree of closeness of the lines of field in the image.

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It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles, (ii) neutrons? Justify your answer.

Solution: i) Due to the fact that they are positively charged, alpha particles serve to generate current in the direction of motion. ii) Because neutrons do not have any charge on them, they do not...

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A magnetic compass needle is placed in the plane of paper near point A as shown in Figure 13.6. In which plane should a straight current-carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what condition is the deflection maximum and why?

Answer: In the plane of the paper itself, to be precise. The axis of the compass is vertical, and the magnetic field produced by the conductor is vertical as well. Because of this, it is not...

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The strength of the magnetic field inside a long current carrying straight solenoid is
(a) more at the ends than at the centre
(b) minimum in the middle
(c) same at all points
(d) found to increase from one end to the other

Solution: Answer is (c) same at all points Magnetic field lines are parallel inside the solenoid. This indicates the existence of a strong magnetic field. As a result, the magnetic field is uniform...

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A constant current flow in a horizontal wire in the plane of the paper from east to west as shown in Figure 13.5. The direction of the magnetic field at a point will be North to South
(a) directly above the wire
(b) directly below the wire
(c) at a point located in the plane of the paper, on the north side of the wire
(d) at a point located in the plane of the paper, on the south side of the wire

Solution: The answer is (b) directly below the wire We can determine the direction of the magnetic field beneath the wire by applying the right-hand thumb rule.

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Choose the incorrect statement
(a) Fleming’s right-hand rule is a simple rule to know the direction of induced current
(b) The right-hand thumb rule is used to find the direction of magnetic fields due to current-carrying conductors
(c) The difference between the direct and alternating currents is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically
(d) In India, the AC changes direction after every 1/50 second

Solution: The answer is (d) In India, the AC changes direction after every 1/50 second In India, the alternating current frequency is 50 Hz. Each cycle, the direction changes twice, so that the...

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In the arrangement shown in Figure 13.4, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then
(a) the deflection in the galvanometer remains zero throughout
(b) there is a momentary deflection in the galvanometer, but it dies out shortly and there is no effect when the key is removed
(c) there are momentary galvanometer deflections that die out shortly; the deflections are in the same direction
(d) there are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions

Solution: The answer is (d) there are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions When the key is plugged in, the galvanometer shows...

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A uniform magnetic field exists in the plane of paper pointing from left to right as shown in Figure 13.3. In the field an electron and a proton move as shown. The electron and the proton experience
(a) forces both pointing into the plane of paper
(b) forces both pointing out of the plane of paper
(c) forces pointing into the plane of paper and out of the plane of paper, respectively
(d) force pointing opposite and along the direction of the uniform magnetic field respectively

Solution: Answer is (a) forces both pointing into the plane of the paper Explanation: The direction of an electron's motion is the polar opposite of the direction of an electric current. This will...

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For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is
(a) The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid
(b) The strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic material like soft iron, when placed inside the coil
(c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
(d) The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Solution: Answer is (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet Because the solenoid behaves similarly...

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For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is
(a) The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid
(b) The strong magnetic field produced inside the solenoid can be used to magnetize a piece of a magnetic material like soft iron when placed inside the coil
(c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
(d) The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Solution: Answer is (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet Explanation: Due to the fact that a...

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A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of the paper and on the axis of the coil) is anti-clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to
(a) A
(b) B
(c) A if the current is small, and B if the current is large
(d) B if the current is small and A if the current is large

Solution: Answer is (a) A Explanation: The magnetic field will be directed from the south pole to the north pole. As a result of field lines pointing from point B to point A, point A is displaying...

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Choose the incorrect statement from the following regarding magnetic lines of the field
(a) The direction of the magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
(b) Magnetic field lines are closed curves
(c) If magnetic field lines are parallel and equidistant, they represent zero-field strength
(d) The relative strength of the magnetic field is shown by the degree of closeness of the field lines

In the case of open magnetic field lines drawn over the horizontal plane ABCD, the magnetic field lines will take the shape of concentric circles, with the centre of each circle located at the axis...

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Choose the incorrect statement from the following regarding magnetic lines of the field
(a) The direction of the magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
(b) Magnetic field lines are closed curves
(c) If magnetic field lines are parallel and equidistant, they represent zero-field strength
(d) The relative strength of the magnetic field is shown by the degree of closeness of the field lines

Answer is (c) If magnetic field lines are parallel and equidistant, they represent zero-field strength Explanation: Due to the fact that parallel lines of magnetism represent a homogenous magnetic...

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Which of the following statement is correct?
(a) A person with myopia can see distant objects clearly
(b) A person with hypermetropia can see nearby objects clearly
(c) A person with myopia can see nearby objects clearly
(d) A person with hypermetropia cannot see distant objects clearly

Solution: Answer is (c) A person with myopia can see nearby objects clearly Myopia is a condition in which a person's ability to see distant objects clearly outweighs his ability to perceive those...

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The focal length of the eye lens increases when eye muscles
(a) are relaxed and the lens becomes thinner
(b) contract and lens become thicker
(c) are relaxed and the lens becomes thicker
(d) contract and lens become thinner

Solution: Answer is (a) are relaxed and the lens becomes thinner When the eye muscles relax and become thinner, the focal length of the eye lens grows in proportion to its thickness. The retina is...

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Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?
(a) Dispersion of light
(b) Scattering of light
(c) Total internal reflection of light
(d) Reflection of light from the earth

Solution: The answer is (b) Scattering of light Explanation: Because red scatters the least amount of light, it may go a long distance. When the sun sets or rises, light has to travel a long...

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The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light
(a) is scattered the most by smoke or fog
(b) is scattered the least by smoke or fog
(c) is absorbed the most by smoke or fog
(d) moves fastest in air

Solution: The answer is (b) is scattered the least by smoke or fog Because the wavelength of red colour is the longest, it may be seen clearly from a long distance. It is the colour that is least...

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Which of the following statements is correct regarding the propagation of light of different colours of white light in air?
(a) Red light moves fastest
(b) Blue light moves faster than green light
(c) All the colours of the white light move with the same speed
(d) Yellow light moves with the mean speed as that of the red and the violet light

Solution: The correct option is C All of the colours in the white light travel at the same speed as one another. Because air is not a dispersive medium, light of all wavelengths travels at the same...

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Twinkling of stars is due to atmospheric
(a) dispersion of light by water droplets
(b) refraction of light by different layers of varying refractive indices
(c) scattering of light by dust particles
(d) internal reflection of light by clouds

Solution: The answer is (b) refraction of light by different layers of varying refractive indices Explanation: The refraction of light maintains the change in the position of the source of light....

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The clear sky appears blue because
(a) blue light gets absorbed in the atmosphere
(b) ultraviolet radiations are absorbed in the atmosphere
(c) violet and blue lights get scattered more than lights of all other colors by the atmosphere
(d) light of all other colors is scattered more than the violet and blue color lights by the atmosphere

Solution: Answer is (c) violet and blue lights get scattered more than lights of all other colors by the atmosphere. Rayleigh's scattering of sunlight is responsible for the blue appearance of the...

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Which of the following phenomena of light are involved in the formation of a rainbow?
(a) Reflection, refraction, and dispersion
(b) Refraction, dispersion, and total internal reflection
(c) Refraction, dispersion, and internal reflection
d) Dispersion, scattering and total internal reflection

Solution: Answer is (c) Refraction, dispersion, and internal reflection Dispersion of light results in the scattering of white light into multiple colours at different angles, resulting in internal...

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A prism ABC (with BC as a base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in Figure 11.1. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky? The Human Eye and the Colourful World CHAPTER11 Fig.11.1
(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)

Solution: The answer is (b) (ii) If the prism is kept with BC at the bottom, a band of colour appears at the bottom that is violet. If the prism is kept with BC at the top, violet will be at the top...

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A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct?
(a) The near point of his eyes has receded away
(b) The near point of his eyes has come closer to him
(c) The far point of his eyes has come closer to him
(d) The far point of his eyes has receded away

Solution: Answer is (a) The near point of his eyes has receded away In hypermetropia, the near spot of the eye is moved away for 25 cm. Thus, in order to read properly, the user needs maintain the...

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An element X of group 15 exists as a diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell.
(a) Identify the element X. How many valence electrons does it have?
(b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?

Solution: Nitrogen is the correct answer, as it possesses five electrons in its outermost shell.

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An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.
(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?
(d) What would be the nature (acidic/ basic) of oxides formed?

Solution: 2FeSO4 Fe2O3+SO2+SO3Sulphur oxides are acidic in nature

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Electropositive nature of the element(s) increases down the group and decreases across the period
(b) Electronegativity of the element decreases down the group and increases across the period
(c) Atomic size increases down the group and decreases across a period (left to right)
(d) Metallic character increases down the group and decreases across a period.
Based on the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(c) Name the element with the smallest atomic size
(d) Name the element which is a metalloid

Solution: (a)The electropositive character of the element(s) increases as it progresses through the group and diminishes as it progresses through time. (b) The element's electronegativity drops as...

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Electropositive nature of the element(s) increases down the group and decreases across the period
(b) Electronegativity of the element decreases down the group and increases across the period
(c) Atomic size increases down the group and decreases across a period (left to right)
(d) Metallic character increases down the group and decreases across a period.
Based on the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(e) Name the element which shows maximum valency.

Solution: (a)The electropositive character of the element(s) increases as it progresses through the group and diminishes as it progresses through time. (b) The element's electronegativity drops as...

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Electropositive nature of the element(s) increases down the group and decreases across the period
(b) Electronegativity of the element decreases down the group and increases across the period
(c) Atomic size increases down the group and decreases across a period (left to right)
(d) Metallic character increases down the group and decreases across a period.
Based on the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(a) Name the most electropositive element among them
(b) Name the most electronegative element

Solution: (a)The electropositive character of the element(s) increases as it progresses through the group and diminishes as it progresses through time. (b) The element's electronegativity drops as...

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Mendeleev ′ predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(c) Classify these elements as metals, non-metals, or metalloids
(d) How many valence electrons are present in each one of them?

Solution: c) Gallium-Group 13 Period 4 is a periodic table of elements. The elements germanium and gallium are both metalloids; however, gallium is a metal. d) Germanium contains four electrons, but...

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Mendeleev ′ predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(a) Name the elements which have taken the place of these elements
(b) Mention the group and the period of these elements in the Modern Periodic Table.

Solution: a) Eka-Silicon was replaced by germanium, while Eka-Aluminum was replaced by gallium. b) Gallium was replaced by germanium. b) Germanium-Group 14 Period 4 (Germanium-Group 14).

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(a) In this ladder (Figure 5.2) symbols of elements are jumbled up. Rearrange these symbols of elements in the increasing order of their atomic number in the Periodic Table.
(b) Arrange them in the order of their group also.

Solution: a) H, He, Li, Be, B, C, N, O, F, Ne, Mg, Al Si, P, S, Cl, Ar, K, Ca b) Group 1:H, Li, Na, K Group 2: Be, Mg, Ca Group 13: B. Al Group 14: C, Si Group 15: N. P Group 16: 0, S Group 17: F. U...

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Complete the following crossword puzzle in figure:
Across:
(1) An element with atomic number 12.
(3) Metal used in making cans and member of Group 14.
(4) A lustrous non-metal which has 7 electrons in its outermost shell.
Down:
(2) Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene.
(5) The first element of the second Period
(6) An element which is used in making fluorescent bulbs and is the second member of Group 18 in the Modern Periodic Table
(7) A radioactive element which is the last member of the halogen family.
(8) Metal which is an important constituent of steel and forms rust when exposed to moist air.
(9) The first metalloid in Modern Periodic Table whose fibres are used in making bullet-proof vests

Solution: Across 1) Magnesium 3) Tin 4) Iodine Down 2) Sodium 5) Lithium 6) Neon 7) Astatine 8) Iron 9) Boron

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