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Q:

A series of fast moving still pictures can be made to appear as a moving picture because the eye 

A) can focus very rapidly as pictures change B) is quicker than the brain
C) can see 2 images separated only if the interval betwen seeing them is more than one-tenth of a second D) can shut out some of the light
 
Answer & Explanation Answer: C) can see 2 images separated only if the interval betwen seeing them is more than one-tenth of a second

Explanation:

The eye can see images separately only if they are exhibited at an interval of more than 1/10 of a second. In the case of a movie, the still pictures come one after the other at less than this minimum interval. So we do not see them separately but only as a continuous moving picture.

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Q:

A car parked in the sun with its windows closed gets terribly hot inside. This is due to 

A) the heat emitted by the engine B) the greenhouse effect
C) the good conducting power of the metal body D) the double layered wind shield
 
Answer & Explanation Answer: B) the greenhouse effect

Explanation:

The green house effect. The waves of smaller wavelength from the sun enter inside the car through the glass windows and are absorbed. The waves of larger wavelength emitted from inside cannot get out through the glass, but remain inside and make it terribly hot.

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Q:

Hot water is poured simultaneously in four metallic tumblers painted outside with different paints. After some time the water will be found to have cooled most in the tumbler painted.

A) rough white B) rough black
C) shining white D) shining black
 
Answer & Explanation Answer: B) rough black

Explanation:

Black surfaces are good emitters of heat. If the black surface is rough too, the emitting will be better. Shinning surfaces reflect black radiation . So if the black surface is also shining the effectiveness of emitting heat is lessened.

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Q:

The base of an electric iron is brightly polished mainly

A) to make it smooth and frictionless B) to make it rust-proof
C) to reduce heat loss by radiation D) to make it more durable
 
Answer & Explanation Answer: C) to reduce heat loss by radiation

Explanation:

Polished surfaces are poor radiators of heat. So loss of heat on that account is reduced and the electric iron remains hotter than otherwise.

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Q:

Tap water is placed in an open pad and allowed to evaporate. After some time the temperature of water 

A) increases to a great extent B) increases slightly
C) decreases slightly D) decreases rapidly
 
Answer & Explanation Answer: C) decreases slightly

Explanation:

Evaporation causing cooling.Here the evaporation is less. Therefore cooling is less.

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Q:

The cover of a solar coker is made of glass because 

A) it absorbs sun's rays B) it reflects sun's rays
C) it retains the heat inside by the green house effect D) it rediates heat better than metals
 
Answer & Explanation Answer: C) it retains the heat inside by the green house effect

Explanation:

As the inside of the cooker is painted black, heat absorption is more producing heat waves of longer wavelength which cannot escape through glass and hence are trapped inside. Thus the food is cooked.

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Q:

A stone floor feels cold to the bare feet but a carpet on the same floor feels warm. This is because 

A) the floor and carpet are at different temperatures B) the stone conveys the heat away from the feet more rapidly than the carpet
C) the carpet is a better conductor of heat than the stone D) the human body maintains a constant temperature
 
Answer & Explanation Answer: B) the stone conveys the heat away from the feet more rapidly than the carpet

Explanation:

Both the floor and the carpet have the same temperature as both are exposed to the same atmosphere. But the former conducts away the heat from the feet better than the carpet as the latter is a non-conductor. So the feet losing more heat, the floor appears cooler to the feet.

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Q:

A cup of hot coffee is placed on a metal table in a room. By which of the following methods does it lose heat?

A) conduction and convection only B) conduction and radiation only
C) convection and radiation only D) conduction, convection and radiation
 
Answer & Explanation Answer: D) conduction, convection and radiation

Explanation:

Part of the heat is conducted away by the metal table. Convection currents in air near the surface of the coffee are set up which accounts for some heat loss. Heat is also lost by radiation from the hot coffee to the surroundings. Most of the heat is lost by the last method.

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