Lakhmir Singh

### A ray of light incident at an angle θ on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5o and the prism is made of a material of refractive index 1.5, the angle of incidence isa) 7.5ob) 5oc) 15od) 2.5o

Answer: a) 7.5o The distance between the refracting surfaces is negligible with thin prisms, thus the prism angle (A) is very small. Because A = r1 + r2, if A is tiny, both r1 and r2 will be little...

### First, a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is ‘n’?

The current is represented as I = E/R+nR when the resistors are connected in series. Current is expressed as 10I = E/(R+R/n) when the resistors are connected in parallel. We get n = 10 by solving...

### In the figure, two positive charges q2 and q3 fixed along the y-axis, exert a net electric force in the +x direction on a charge q1 fixed along the x-axis. If a positive charge Q is added at (x,0) the force on q1 a) shall increase along the positive x-axis b) shall decrease along the positive x-axis c) shall point along the negative x-axis d) shall increase but the direction changes because of the intersection of Q with q2 and q3

the correct option is a) shall increase along the positive x-axis.

### Mars has approximately half of the earth’s diameter. When it is closer to the earth it is at about ½ AU from the earth. Calculate at what size it will disappear when seen through the same telescope.

$D_{mars}/D_{earth}=1/2$ Also, $D_{earth}/D_{sun}=1/100$ So, $D_{mars}/D_{sun}=1/2\times 1/100$ At 1AU, the sun’s diameter is = (1/2) degree Therefore, diameter of mars will be = (1/400) degree At...

### a) How many astronomical units (AU) make 1 parsec?b) Consider the sun like a star at a distance of 2 parsec. When it is seen through a telescope with 100 magnification, what should be the angular size of the star? Sun appears to be (1/2) degree from the earth. Due to atmospheric fluctuations, eye cannot resolve objects smaller than 1 arc minute.

a) 1 parsec is the distance at which 1 AU long arc subtends an angle of 1s, according to the definition. Using the definition, we can write, 1 parsec = (3600)(180)/π AU = 206265 AU = 2 × 105 AU b)...

### Name the device used for measuring the mass of atoms and molecules.

Mass spectrograph is a tool for determining the mass of atoms and molecules.

### Which of the following ratios express pressure?a) Force/areab) Energy/volumec) Energy/aread) Force/volume

Correct answers are a) force/area and b) energy/volume

### A particle is in linear simple harmonic motion between two points, A and B, apart. Take the direction from to as the positive direction and give the signs of velocity, acceleration and force on the particle when it is(a) at away from A going towards , and(b) at away from B going towards .

(a) Positive, Positive, Positive From the end $A$, the particle is travelling toward point 0. This motion is going from $A$ to $B$, which is the standard positive direction. As a result, the...

### A mild steel wire of length and cross-sectional area is stretched, well within its elastic limit, horizontally between two pillars. A mass of is suspended from the mid-point of the wire. Calculate the depression at the midpoint.

Water pressure at the bottom is given as, $p=1000 a t m=1000 \times 1.013 \times 10^{5}$ Pa $p=1.01 \times 10^{8} \mathrm{~Pa}$ Initial volume of the steel ball is given as $V=0.30 \mathrm{~m}^{3}$...

### Explain what is observed when (i) when a beam of light is passed through a colloidal sol,(ii) an electrolyte NaCl is added to hydrated to ferric oxide sol, and(iii) electric current is passed through a colloidal sol?

Solution:- (i) When a beam of light is transmitted through a colloidal solution, light scattering is detected. This phenomenon is called the Tyndall effect. The path of the beam is...

### Define emulsions. What are their different types? Give examples of each type.

The colloidal solution in which both the dispersed phase and the dispersion medium are liquids is known as an emulsion. Emulsions are divided into two categories: (a) Oil in water type: The...

### Describe some features of catalysis by zeolites.

Some features of catalysis by zeolites are listed below:- (i) Zeolites are alumino-silicates that are naturally microporous. (ii) Because of their honeycomb-like structure, zeolites are...

### What do you mean by activity and selectivity of catalysts?

a) Activity: The ability of a catalyst to enhance the rate of a reaction is referred to as its activity. The main factor, chemisorption, determines a catalyst's activity. The process should be...

### Give four examples of heterogeneous catalysis.

(i) Sulphur trioxide is generated when sulphur dioxide is oxidised. Pt acts as a catalyst in this process. 2SO2(g) ​→ Pt(s) + ​2SO3(g)​ (ii) Ammonia is formed when dinitrogen and dihydrogen are...

### The action of soap is due to emulsification and micelle formation. Justify.

The cleansing activity of soap is determined by emulsification and micelle production. The basic combination of soap contains sodium and potassium salts of long-chain fatty acids (R-COO-Na+). The...

### How do emulsifiers stabilize emulsion? Name two emulsifiers.

Emulsifiers stabilise an emulsion by lowering the interfacial tension between the two liquids that make up the emulsion. Emulsifiers are long-chain compounds having polar groups. For instance,...

### How are colloids classified on the basis of – (i) physical states of components (ii) nature of dispersed phase and (iii) interaction between the dispersed phase and dispersion medium?

Colloids are classified in a variety of ways : (I) The dispersed phase and dispersion medium, or the physical state of the components, are referred to as components. As a result, depending on...

### Define lyophilic and lyophobic sols. Give one example of each type. Why are hydrophobic sols easily coagulated?

Lyophilic sols - Lyophilic sols are colloidal sols made by combining ingredients like gum, gelatin, starch, and others in a liquid called the dispersion medium. These sols are reversible in nature....

### How do pressure and temperature affect the adsorption of gases on solids?

Effect of pressure : Because adsorption is a reversible process that is accompanied by a decrease in pressure, adsorption increases as pressure rises. Effect of temperature : According to...

### Write the classification of colloidal solutions on the basis of physical states of the dispersed phase and dispersion medium.

Colloidal solutions can be classified as follows on the basis of their dispersed phase and dispersion medium :   Dispersed phase Dispersion medium Type of colloid Example 1. Solid Solid Solid Sol...

### Why is adsorption an exothermic process?

The process of adsorption is always exothermic. There are two ways to understand this which are as follows :- (I) The residual forces on the adsorbent's surface are reduced as a result of...

### What is the role of adsorption in heterogeneous catalysis?

Heterogeneous catalysis is a catalytic process in which the catalyst and reactants are present in different phases. This form of heterogeneous catalytic action is explained by the adsorption theory....

### What is the activation of adsorbent? How is it achieved?

Activation of adsorbent is the process of increasing the adsorption power of the adsorbent. The following methods are used to activate adsorbents: (I) Increasing the adsorbent surface area. This can...

The plot of the amount of adsorption (x/m) against the pressure of the gas (P) at constant temperature is known as the adsorption isotherm (T). Three cases arise from the graph which are as follow...

### Write the factors influencing the adsorption of a gas on a solid.

Factors influencing the adsorption of gas on a solid:- (1) Nature of the gas : Easily liquefiable gases, such as NH3, HCl, etc., have strong Van der Waal forces, so they are adsorbed to a greater...

### Why is a finely divided substance more effective as an adsorbent?

Because adsorption is a surface phenomenon, it is directly proportional to the surface area. Due to its large surface area, a finely split material acts as a good adsorbent. With an increase in...