Heat is the form of energy which is transferred between two substances at different temperatures. The direction of the flow of energy is from the substance of higher temperature to the substance of lower temperature. Heat is usually measured in units of energy i.e. calories or joules. Heat and temperature should not be used interchangeably, but this is incorrect. The temperature will measure the hotness or coldness of a substance. In this article, we will discuss the heat formula with examples. Let us learn the concept!
Heat Formula
What is the concept behind heat?
Heat is the transfer of kinetic energy from one medium to another medium via energy source. This energy transfer can occur in three different ways which are radiation, conduction, and convection. Heat is a form of energy which produces a change in the temperature of any substance.
Also, the temperature is the average kinetic energy per molecule of that substance. Temperature is measured in different scales as Celsius (C), Fahrenheit (F) and Kelvins (K). Therefore, in a simple way temperature is how hot or cold an object is. On the other hand, heat is the energy that flows from a hotter object to a cooler object.
Due to heat thermal expansion may occur. It is a phenomenon that takes place in solids, liquids, and gases. Almost all substances expand with an increase in the temperatures. For example, due to the heating of air in a hot air balloon, the balloon expands and rises. In every case, thermal expansion occurs in response to the increase in temperature and devices may take advantage of this concept.
Heat by conduction takes place when two objects are kept in direct contact. Also, the temperature of one is higher than the other. The temperature tends to equalize and due to which the heat conduction consists of the transfer of kinetic energy from warmer medium to a cooler one.
We denote heat is denoted by Q.
The Heat formula is:
C = \(\frac{Q}{m\Delta T}\)
Where,
| C | specific heat, |
| m | mass of the body, |
| \(\Delta\) | temperature difference. |
We generally use Heat formula to find out the heat transfer, mass, specific heat or temperature difference in a given situation. Heat is expressed in units of Joules (J).
Solved Examples
Q.1: Determine the heat needed to raise a 1 kg of iron from 250° C to 600° C?
Solution:
As given in the problem,
Mass, m = 1 Kg,
Specific heat of iron, C = 0.45 \(Jg^-1°C \)
Also, temperature difference,
\(\Delta T = 700° C – 250° C \)
\(\Delta T = 450° C \)
Now applying the heat formula,
\(c = \frac{Q}{m\Delta T} \)
rearranging the formula
\(Q = mc\Delta T \)
\(Q = 1 \times 0.45 \times 10^3 \times 450\)
= 20.25 J
Q. 2: Determine how much heat energy is lost if 50 Kg water is cooled from 600\degreeC to 200\degreeC. Specific heat of water is given as \(C = 4.2 \times10^3 JKg^-1° C.\)
Solution:
Given values are,
Mass of water, m = 50 Kg,
Specific heat of water, C = \(4.2 \times10^3 JKg^-1°\)
Temperature difference,
\(\Delta T = – 40°\)
Heat energy by formula is,
Q = \(mc\Delta T \)
Q = \(50 \times 4.2 \times 10^3 × (-400 ) \)
Q= – 840 J
