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Q:

Formation of shadows can be explained by 

A) rectilinear propagation of light B) reflection
C) refraction D) total internal reflection
 
Answer & Explanation Answer: A) rectilinear propagation of light

Explanation:

In this position, the head light will be at the principal focus so that the rays of light falling on the cancave mirror will be rendered parallel

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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:

Radio waves sent out by a radio stations are reflected by

A) troposphere B) stratosphere
C) mesosphere D) ionosphere
 
Answer & Explanation Answer: D) ionosphere

Explanation:

This is a layer of atmosphere about 60 to 70 km above the earth and extends to about 400km. It contains ionised particles which can reflect radio waves making radio communication round the world possible.

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Q:

Skating on ice is possible because 

A) the surface of ice is smooth B) ice is cold
C) the pressure on the ice due to skate melts the ice by lowering its melting point forming a thin film of water D) the pressure on the ice due to skate raises its melting point
 
Answer & Explanation Answer: C) the pressure on the ice due to skate melts the ice by lowering its melting point forming a thin film of water

Explanation:

Here is a case of  lowering of melting point of ice with increase of pressure

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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:

In a freezer ice cubes will be formed more quickly in trays made of 

A) rubber B) plastic
C) aluminium D) wood
 
Answer & Explanation Answer: C) aluminium

Explanation:

Aluminium being a good conductor of heat conducts away the heat from the substance quite easily and causes quick freezing.

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