Question

The quantity of heat required to change the temperature of one gram of a water by one degree Celsius is known as
A. 1 joule
B. 1 kilocalorie
C. 1 calorie
D. 1 ampere

Answer 1

Heat is the energy that is transferred between systems when they are at different temperatures. The S.I. unit of heat is Joule named after English physicist James Prescott Joule and is represented by the letter J. Joule is a derived unit, its actual unit is $kg.{{m}^{2}}.{{s}^{-2}}$ . Here, by one degree it is meant, the change in temperature from ${{14.5}^{\circ }}C$ to ${{15.5}^{\circ }}C$ .

Complete answer:
Let’s say we have two blocks of some materials, one hot and one cold each attached to a thermometer (a device used to measure temperature). If we keep the two bodies in contact then after some time, they will attain an equilibrium temperature (both bodies will be at the same temperature). Why does this happen?
This happens because of the flow of something called heat. So, what is heat? Heat is a form of energy that flows from one object to another. So, the next question you should be asking is what kind of energy? Well, of course, it is the flow of kinetic energy and it is important to remember that temperature is the average kinetic energy. The S.I. The unit of heat is Joule and its C.G.S. The unit is calories.
1 calorie = 4.186 Joule
So, we can say the flow of heat changes the temperature of the system but exactly by how much? It depends on two things, the first is the mass of the system (the more mass a system has the more heat is required to raise its temperature) and the second is the specific heat. So, now the question arises: what is specific heat? Well in layman’s it is the measure of how well a substance can store heat. Every substance has its own specific heat and the higher it is, the more energy transfer (in the form of heat) it takes to change its temperature. Now, we consider water and aluminum, water has a very high specific heat as compared to aluminum. That means we would need much more heat to change the temperature of water compared to aluminum.
Now, let’s get back to the real question here. In general, the amount of heat (Q) transferred to or from a substance is equal to the mass (m) times the specific heat (c) times the change in temperature $(\Delta T)$ . Mathematically,
$Q=mc\Delta T$
The C.G.S. The unit of heat is calories. 1 calorie is defined as the amount of heat required to raise the temperature of the water ${{1}^{\circ }}C$ .
So, the correct answer to this question is 1 calorie i.e. option C.

Note:
When we are talking about ${{1}^{\circ }}C$ in the above definition of one calorie we specifically mean raising the temperature from ${{14.5}^{\circ }}C$ to ${{15.5}^{\circ }}C$ . The direction of heat flow is from a hot body to a cold body. If Q is positive heat is flowing into the system and if Q is negative its means heat is flowing out of the system.