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 Physics Questions

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Q:

Heat transfer by radiation mainly depends upon

A) Kind and extent of its surface B) Its temperature
C) Nature of the body D) All of the above
 
Answer & Explanation Answer: D) All of the above

Explanation:

Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region. It depends on nature of the body, its temperature and kind & extent of its surface.

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4 3374
Q:

A nuclear reactor is said to have become 'critical' when 

A) it stops due to malfunctioning B) it starts emitting dangerous radioactive radiations
C) it is shut down to avoid explosion D) it is ready to produce controlled energy
 
Answer & Explanation Answer: D) it is ready to produce controlled energy

Explanation:

To produce controlled energy i.e energy at a controlled or steady rate, the number of fissions per second must be controlled and maintained at that rate. Excess neutrons should be absorbed by control roads like cadmium.

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4 3368
Q:

One light year is approximately equal to

A) 10^12 mts B) 10^16 mts
C) 10^11 mts D) 10^13 mts
 
Answer & Explanation Answer: B) 10^16 mts

Explanation:

Light year is the unit of to express astronomical distances, that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.

 

Approximately, 1 light year = 10^16 mts.

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4 3347
Q:

Pick out the only vector quantity

A) pressure B) impulse
C) gravitational potential D) co-efficient of friction
 
Answer & Explanation Answer: B) impulse

Explanation:
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5 3317
Q:

A Fuse is used in mains electric supply as a safety devices. Which one of the following statements about the fuse is correct?

A) It is connected in parallel with the main switch B) It is made mainly from silver alloys
C) It must have a low melting point D) It must have a very high resistance
 
Answer & Explanation Answer: C) It must have a low melting point

Explanation:
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15 3303
Q:

Heat energy of an object is

A) the average energy of the molecules of the object B) the total energy of the molecules of the object
C) the average velocity of the molecules of the object D) the average potential energy of the molecules of the object
 
Answer & Explanation Answer: B) the total energy of the molecules of the object

Explanation:
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5 3292
Q:

Heat is associated with

A) K.E of random motion of molecules B) K.E of orderly motion of molecules
C) Total K.E of random and orderly motion of molecules D) None of these
 
Answer & Explanation Answer: A) K.E of random motion of molecules

Explanation:
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5 3287
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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