Question

Pins Q, P, R, and S are attached to the iron rod with the help of wax as shown below. In which ascending order the pins are likely to fall?

• A. P, Q, R, S
• B. Q, P, R, S
• C. S, R, Q, P
• D. S, R, P, Q

Answer 1

The correct option is A P, Q, R, S

We know that in a solid predominant mode of heat transfer is conduction and iron is a good conductor of heat. Here, Pins Q, P, R, and S are attached to the iron rod with the help of wax.

As soon as the heat comes to the pins it will melt the wax and hence the pin will fall down. So once we find which pin felt the heat first we can identify the order in which the pins will drop.

We know that heat always flows from a higher temperature body to a lower temperature body, here the high-temperature source(candle flame) is in between the P and R pins. Initially, all the pins are at room temperature which is comparatively lower than the temperature of the flame of the candle and hence heat from the candle flame starts to flow in both directions (towards pins P and Q and towards pins R and S).

Pin P is 4 cm away from the candle flame, hence it will capture the heat first, then pin Q, as it is only 8 cm away from the candle flame.

Pin R is 10 cm away from the candle flame. Hence it will capture the heat after pin Q and at last heat will meet at pin S which is 20 cm away from the candle flame.

So the correct order is P, Q, R, and S.