Capital

SET-I 1. Give two examples of motion in which the accelerations is non-zero but the velocity is zero. ⇒ In projectile motion, the velocity at the highest point of the path is zero but acceleration is equal to ‘g’. Similarly in SHM, velocity is zero but acceleration has maximum value at the extreme position. 2. Why is it easier to hold a load with arm folded than outstretched? ⇒ 3. Why is it easier to swim in sea water than in river water? ⇒ Due to the dissolution of mineral salts, the density of sea water is greater than that of river water. Therefore weight of the same volume of displaced water is greater for sea water than river water. Hence more upthrust is experienced in sea water and becomes easier to swim. 4. Calculate the dimensional fomula for universal gravitational constant ‘G’. ⇒ [M-1L3T-2] 5. A piece of ice is floating in water. Will the water level rise if the ice melts completely? ⇒ No, there is no change in the level of water because due to anomalous expansion of water, volume of certain mass of ice is greater than volume of same mass of water at 00C. When this ice melts the volume of the exposed part of ice in air is compensated by decrease in volume. Hence the level of water remains unchanged. 6. Steam at 100o C causes more severe burns than water at 1000C? ⇒ Each gram of steam at 100oC has 539 calories more heat than 1 gram of water at 100oC.So one can get more severe burn from steam at 1000C than water at 100oC. 7. Dew is formed in the grass blades but not on the leaves of a tall tree. Why? ⇒ During the night, the earth surface radiates heat and temperature falls. Grass is very near the earth surface so it also becomes cooler. This causes the condensation of water vapor and deposition on the grass blades as dew. But tree leaves are at greater height than grass. As the water vapor in contact with these leaves cools down slightly, it becomes heavier and comes down. Hot air above this layer comes to fill this space. This process continues so that the air in contact with tree leaves can not be sufficiently cooled to form dew on the leaves.

8. It is possible to seal a platinum wire into a glass tube but not a brass wire. Why? ⇒ 9. Can a plane mirror ever form a real image? Explain. ⇒ Yes, if convergent beam of light from a source falls on a plane mirror, the object for the mirror will be virtual and image will be real( Draw diagram ). 10. Does the focal length of a lens change when immersed in water? Will it increase or decrease? ⇒ For a lens, focal length is given by 1/f = (µ2/µ1-1)(1/r1+1/r2) where µ2 is focal length of lens material and µ1 that of water. For the lens in air 1/f = (µ2-1)(1/r1+1/r2). Comparing these two relations, we see that 1/f decreases and f increases when lens is immersed in water. 11. Why does the sky appear blue? ⇒ When sunlight passes through the earth’s atmosphere, it gets scattered by very small gaseous particles of the atmosphere. Wavelength of blue color is smaller than the red color. Therefore blue light is scattered more than the red light. 12. Classify Dia, Para and Ferro magnetic substances on the basis of permeability? ⇒ Permeability is little less than unity, a little greater than unity, and very high in case of Dia, Para and Ferro magnetic substances respectively. 13. Why can more charge be stored on a metal sphere if it is highly polished than when its surface is rough? ⇒ 14. Soft iron is easier to demagnetize than steel. Why? ⇒ The coercivity of soft iron is less than that of steel. This results the area of hysteresis loop for soft iron smaller than that for steel. Thus the loss of energy per cycle is less for iron than for steel. 15. A large number of free electrons are present in metals. Why there is no current in the absence of electric field across it? ⇒ 16. Distinguish between primary and secondary cells. Primary cell A primary cell can not be recharged. Emf of primary cell is low.

Secondary cell It can be charged. Emf of secondary cell is high.

17. Why do we prefer a potentiometer to measure emf of a cell rather than a voltmeter? ⇒ When a voltmeter is connected in an electrical circuit, it draws some current from the cell. So it measures only the p.d. whereas potentiometer is used to measure emf because at null point where no current is drawn from the cell and exact emf can be recorded.

SET-II 1. In the equation (P+a/V2)(V-b) = RT, what are the dimensions of constants a and b? ⇒ a = [ML5T-2] ⇒ b= [L3] 2. The positively charged nucleus attracts the electron in the orbits. Why do the electrons not collapse into the nucleus? ⇒ Because the force of attraction due to nucleus and electron is balanced by centripetal force necessary to keep the electron in the circular path. 3. Why is it difficult to run fast in sand? ⇒ 4. Why is the bottom of the ship made heavy? ⇒ 5. A ballet dancer stretches her arms to reduce her motion. Explain? ⇒ 6. Why is invar used in making clock pendulum? ⇒ 7. Two shirts are warmer than single shirt of double thickness. Why? ⇒ 8. Why dews are formed in early morning hours? ⇒ In the early morning hours, the temperature of the atmosphere near the earth’s surface becomes minimum. If this temperature is below dew point, then water vapor is condensed as dew in these hours. 9. Define luminous flux. State its unit of measurement. ⇒ It is defined as the luminous energy emitted per sec by a source. Its unit is Lumen. 10. Explain why a mirror cannot give rise to chromatic aberration? ⇒ 11. An air bubble in a jar of water shines brightly. Explain why?

⇒ 12. Two magnetic lines of force can not intersect each other. Why? ⇒ Since the tangent to any point on magnetic lines of force gives the direction of magnetic field intensity at that point, if two magnetic lines of force intersect at a point there will be two magnetic intensities at a point which is not possible. 13. Sharp points are strictly avoided in electrical machines. Why? ⇒ If there is a sharp point in machines, the surface charge density will be maximum at the point. The particles of air which come in contact with the sharp point are repelled away from the sharp point. Other fresh air comes to fill the position of repelled air. They are also repelled. This process is repeated and we get a continuous flow of electric wind. This results in leakage of charge at the sharp point. 14. What is tangent law? ⇒ When a magnet is freely suspended in a region where two uniform magnetic fields, F and H applied simultaneously normal to each other, then the tangent of inclination of magnet with H is given by F/H which is tangent law. 15. Two bulbs of 60 W and 100 W are connected in series and this combination is connected with the mains. Which bulb will glow more brightly? Explain. ⇒ The resistance of 60W bulb is greater than that of 100W bulb. The brightness depends on power consumed (P=I2R). Hence the 60W bulb (greater resistance) will be brighter. 16. An ammeter is always connected in series. Why? ⇒ An ammeter is a low resistance device which when connected in series does not disturb the current flowing through the load. So it measures actual current in the circuit. Hence it is always connected in series. 17. What is neutral temperature? On what factor does it depend? ⇒ The temperature of inversion at which the thermo emf becomes maximum is called the neutral temperature. It depends upon nature of the metals.