IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Heat of a One Rupee Coin

Objective

To know that metals are good conductors of heat.

Apparatus

one rupee coin, piece of paper, candle.

Procedure

Keep a paper stretched and bring it above a candle. Observe how easily it burn.

Now, wrap the paper tightly over a coin and hold it with your left hand or by a fork. Bring the paper above the flame for few seconds. The paper does not burn. Remove the paper and touch the coin. You will feel it hot.

Discussion

In first case (paper without coin), the flame of the candle would raise the temperature of the paper above its ignition point. Hence the paper burns immediately.

A metal is good conductor of heat. Hence when paper tightly wrapped over the coin is brought over the flame, the heat of the flame is quickly transferred from the paper to the coin. Due to this, the temperature of the paper would not rise above its ignition point. Hence paper did not burn. The coin gets heated up because it is good conductor of heat.

If instead of coin, a piece of wood or plastic was taken, the temperature of the paper will rise above ignition point and the paper will burn, because wood and plastic are bad conductors of heat.

Note

Hazard: be careful while handling the flame.