Question

What is the value of 1 calorie in Joules?
A. 9 Joules
B. 4.18 Joules
C. 4.16 Joules
D. 8 Joules

Answer 1

Hint: We are asked to do the conversion of 1 calorie into Joules. Both calorie and Joules are the units of energy in different unit systems. 1 calorie is simply the amount of heat energy used to raise the temperature of 1 gram of water by \[1{}^\circ C\]. There is no mathematical derivation for the conversion of calorie into Joule. Their relation is merely empirical.

Complete answer:
In the question we are asked to convert 1 calorie into Joules.
We know that both Calorie and Joules are the units of energy. But calorie is the unit of energy in the metric system whereas Joule is the SI unit of energy.
A calorie can be defined as the measure of the total amount of heat energy required to raise the temperature of 1 gram of water by $1{}^\circ C$.
For a kilocalorie, it is defined as the measure of the total amount of heat energy required to raise the temperature of 1 kilogram of water by $1{}^\circ C$.
1 calorie is given as 4.18 Joules and 1 Joule is given as 0.238 Joules.

So, the correct answer is “Option B”.

Note:
We know that the quantity of heat represented by the calorie will vary at different temperatures. Hence it was necessary to define the temperature at which the specific heat of water is taken as 1 calorie. Therefore $15{}^\circ $ calorie is defined as the amount of heat which will raise the temperature of 1 gram of water from $14.5{}^\circ C$ to $15.5{}^\circ C$. This amount of heat, i.e. $15{}^\circ $ calorie is equal to 4.18 Joules.