371. Cooling of Air conditioner is done by-

1. Flow of water
2. Release of compressed gas
3. Cooking gas
4. Melting the solid

Option “2” is correct.
Most of the air conditioner uses compressed gas, which can cool the room or other places.
372. The red colour of the Sun at sunset and sunrise is due to-

1. Scattering of light
2. Refraction of light
3. Total internal reflection of light
4. Dispersion of light

Option “1” is correct.
Red has the maximum wavelength. During sunrise and sunset, the rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore light other than red is mostly scattered away. Most of the red light which is least scattered enters our eyes. Hence, the sun and the sky appear red.
373. Reading glasses to see near objects use which type of lens?

1. Concave
2. Convex
3. Plain
4. None of these

Option “2” is correct.
A convex lens is thicker in the middle and thinner at the edges. Rays of light that pass through the lens are brought closer together. A convex lens is also called a converging lens. A convex lens is also used in reading glasses & it also used to remove the defect of farsightedness.
374. The focusing in the eye is done by-

1. Change in the convexity of the lens
2. To and fro movement of the lens
3. To and fro movement of the retina
4. Change in the refractive index of the eye fluid

Option “1” is correct.
The refractive or bending power of the cornea and humor is constant. However, that of the lens can be changed by changing its shape. That is making it more or less convex so that light can be properly focused on the retina. The greater the lens convexity or bulge the more bends the light. The flatter the lens, the less it bends that light.
375. The mirror, which is used in searchlights, is-

1. Concave mirror
2. Convex mirror
3. Simple mirror
4. None of these

Option “1” is correct.
Concave mirror is used in the headlights of cars and in searchlights. A light placed at the focus of a concave lens can form a parallel beam and is used in car headlights and searchlights.
376. In an earthen pitcher, the water remains cold due to the process of-

1. Condensation
2. Evaporation
3. Sublimation
4. None of the above

Option “2” is correct.
The water remains cold in an earthen pitcher because of a physical process is known as evaporation, when liquid changes to a gaseous (or vapour) state without boiling, it is known as evaporation.
377. The velocity of sound in air is approximately-

1. 10 km/sec.
2. 10 mile/min.
3. 330 m/sec.
4. 3 × 10/sec.

Option “3” is correct.
Velocity of sound in air is 330m/sec.
378. A wire with black insulation during electric supply is-

1. Live wire
2. Earth wire
3. Neutral wire
4. Fuse wire

Option “3” is correct.
The electric power line reaches our house through three wires namely a live wire, neutral wire, and earth wire. To avoid confusion we follow a colour code for insulating these wires. The red wire is a live wire, and the black wire is neutral. The earth wire is given green plastic insulation.
379. Light year is the unit of-

1. Distance
2. Time
3. Speed of light
4. Intensity of light

Option “1” is correct.
Light year is a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.46 × 1015 meters.
380. The apparatus used to measure the intensity of light is known is-

1. Anemometer
2. Colorimeter
3. Luxmeter
4. Altimeter

Option “3” is correct.
Luxmeter is used to measure the intensity of light, while colorimeter is a device used to measure the intensity of colour.
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