PHYSICS GENERAL KNOWLEDGE QUESTIONS

31.

On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because

A.	mercury is a metal
B.	density of mercury is greater than that of water
C.	cohesion of mercury is greater than its adhesion with glass
D.	cohesion of water is greater than its adhesion with glass

Answer: Option C

Explanation:

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32.

Suitable impurities are added to a semiconductor depending on its use. This is done in order to

A.	increase its life
B.	enable it to withstand higher voltages
C.	increase its electrical conductivity
D.	increase its electrical resistivity

Answer: Option C

Explanation:

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33.

Stars twinkle because

A.	the intensity of light emitted by them changes with time
B.	the distance of the stars from the earth changes with time
C.	the refractive index of the different layers of the earth’s atmosphere changes continuously, consequently the position of the image of a start changes with time
D.	the light from the star is scattered by the dust particles and air molecules in the earth’s atmosphere

Answer: Option C

Explanation:

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34.

It takes much longer to cook food in the hills than in the plains, because

A.	in the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100^oC causing an increase in cooking time
B.	due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100^oC and therefore water takes longer to boil
C.	in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere
D.	in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking