Physics 2006 JAMB Past Questions - Question 45: A drop of petrol makes a finger colder than a drop of water would because

Correct Answer

B

Explanation

A drop of petrol makes a finger feel colder than a drop of water because of differences in thermal conductivity and specific heat capacity.

1. Thermal Conductivity: Water has a higher thermal conductivity compared to petrol. This means that water is better at conducting heat away from your finger than petrol. When you touch a drop of water, it can quickly absorb heat from your skin, making you feel cold. On the other hand, petrol is a poorer conductor of heat, so it doesn't absorb heat as effectively, and therefore, it doesn't draw heat away from your skin as rapidly.

2. Specific Heat Capacity: Water also has a relatively high specific heat capacity, which means it can absorb and store a significant amount of heat energy per unit of mass. When you touch water, it takes some time to heat up to the temperature of your skin, and this process draws heat away from your skin, making it feel cold. Petrol, in comparison, has a lower specific heat capacity, so it doesn't absorb and store heat as efficiently as water. Therefore, it doesn't draw heat away from your skin as effectively.

In summary, the higher thermal conductivity and specific heat capacity of water make it feel colder when you touch it compared to petrol, as it can quickly absorb heat from your skin, causing a cooling sensation.