41. The heat required in calories to convert one gram of ice at 0 °C to steam at 100°C is approximately

1. 80
2. 336
3. 720
4. 620

Option “3” is correct.
Latent heat of Melting = 80 calorie/gram
The heat required for ice at 0°C to convert in water = 80 calorie
Required heat to enhance the temperature of water from 0°C to 100°C = 100 calorie
Latent heat of vaporization = 540 calorie/gram
Hence the energy required to convert water into vapour at
100°C = 540 calorie.
Total heat required = 80 + 100 + 540
= 720 calorie.
42. What is absolute zero temperature?

1. The starting point of any temperature scale
2. Theoretically the lowest possible temperature
3. The temperature at which the vapour of any liquid substance is condensed.
4. The temperature at which all material in vapour form

Option “2” is correct.
Absolute zero is the lowest possible temperature at which point the atoms of a substance transmit no thermal energy. They are completely at rest. It is 0 degrees on the Kelvin scale, which translates to-273.15 degree Celsius.
43. A body floats at 4°C water. If temperature reaches 100°C then-

1. The body will sink
2. No change
3. More part of the body will submerge
4. The body will float freely

Option “1” is correct.
When the water is heated, its density decreases. The density of the water at 100°C is at the lowest, so the body will sink. Water density is maximum at 4°C, so the body will float.
44. Why it is easier to swim in the sea than in a river?

1. The sea water is salty
2. The sea water is deep
3. The sea water is heavier
4. The sea water is lighter

Option “1” is correct.
It is easier to swim in sea water than in a river because, the sea water contains salt which increases the density of water and also increases its upthrust so, the chances of sinking get reduced and one can easily swim in such water.
45. Light from the Sun reaches Earth in about:

1. 2 minutes
2. 4 minutes
3. 8 minutes
4. 16 minutes

Option “3” is correct.
The sunlight takes about 500 second or 8 minutes (apx) to reach to the earth.
46. When light waves pass from air to glass the variable affected are-

1. Wavelength, frequency and velocity
2. Velocity and frequency
3. Wavelength and frequency
4. Wavelength and velocity

Option “4” is correct.
When light passes from air to glass or one medium to another, then the frequency of the light remains constant but wavelength and velocity are changed.
47. The atmosphere exerts enormous pressure on us. But, we do not feel it because

1. Our blood exerts a pressure slightly more than that of the atmosphere.
2. We are used to it.
3. Our bones are very strong and can withstand the pressure.
4. The surface are of our head is very small.

Option “1” is correct.
The atmosphere exerts enormous pressure on us but we do not feel it, because our blood exerts pressure slightly more than that of the atmosphere. We feel this pressure in water because the pressure underwater is greater than our normal blood pressure.
48. Assertion (A) : With the increase of temperature, the viscosity of glycerin increases.
Reason (R) : Rise of temperature increases kinetic energy of molecules.
Code:1. Both (A) and (R) are true, and (R) is the correct explanation of (A).
2. Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3. (A) is true, but (R) is false.
4. (A) is false, but (R) is true.
Option “4” is correct.
The temperature dependence of liquid (Glycerin etc) viscosity is the phenomenon by which liquid viscosity tends to decrease as its temperature increases. The increase in temperature causes the kinetic or thermal energy to increase and the molecules become more movable.
49. Food gets cooked faster in a pressure cooker because-

1. Water starts boiling at a lower temperature due to high pressure
2. Water starts boiling at a higher temperature due to high pressure
3. Water boils only at 100° C but the heat content is higher at high pressure
4. Convection currents are set inside the cooker

Option “2” is correct.
Food can be cooked faster in a pressure cooker since the boiling point of water increases with pressure. As the water boils, the steam produced cannot evaporate so the pressure inside the cooker increases. At higher elevations, atmospheric pressure is lower and therefore water boils at lower temperature.
50. In cold countries, alcohol is preferred to mercury as a thermometric liquid because:

1. Alcohol has a lower freezing point
2. Alcohol is a better conductor of heat
3. Alcohol is cheaper than mercury
4. The world production of alcohol is greater than that of mercury

Option “1” is correct.
There are lots of reasons for using alcohol than mercury as thermometric liquids. Some alcohol has a very low freezing point of about-112°C and therefore is suitable to record very low temperature.
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