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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:

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:

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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Q:

A solid ball of metal has a spherical cavity inside it. When the ball is heated the volume of the cavity will

A) increase B) decrease
C) remain unaffected D) have its shape changed
 
Answer & Explanation Answer: A) increase

Explanation:

The metal ball can be considered  to be made up of several layers of thinner ones. On heating each of these layers will increase in radius. As the inner most layer also increases its radius, the volume inside it i.e, the volume of the hollow portion will also increase.

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Q:

For accurate scientific work, temperatures are often measured by

A) mercury thermometers B) alcohol thermometers
C) platinum resistance thermometers D) thermoelectric thermometers
 
Answer & Explanation Answer: C) platinum resistance thermometers

Explanation:

The resistance of metallic conductors e.g, platinum, increases with rise of  temperature . The increase in temperature results in a decrease of current which can be recorded in a galvanometer if the conductor is included in an electrical circuit. Thus the temperature can be known; platinum resistance thermometer is used generally for accurate scientific work. When two dissimilar metals are joined at the ends, and these ends are subjected to a difference of temperature, a current flows through the metals. Greater the difference of temperature , greater the current. So the curent strength can form the basis for measuring the difference in temperature. And when one of these temperatures is known, we can calculate the other.

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Q:

A man stands on the pan of a balance holding a fish in his right hand and bucket of water in his left hand. If he transfers the fish into the bucket, the total weight on the pan

A) increases B) decreases
C) remains the same D) first increases and then decreases
 
Answer & Explanation Answer: C) remains the same

Explanation:

Before transferring the fish, the position is the man with the fish and the bucket of water. After transferring the position is : the man without the fish, but the fish inside the water in the bucket. Thus to know whether there is any change in weight, it is enough to consider whether there is any change in weight when the fish in air is transferred into the water. The answer is there is no change as when in water though it loses weight due to upthrust of water on it, the level of water increases and exerts an equal force at the bottom

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