Unit of heat
The S.I unit of heat is Joule.
One Joule is defined as the amount of work done on a body when a force of 1 Newton displaces a body at a distance of 1m in the direction of the force.
1 Joule = Nm
1 N = 1kg m/s2
1 Joule = kg m/s2 x m
1 Joule = kg m2/s2
Other forms of Joule
Let’s discuss other units in the form of Joule.
1 Joule = Pa. m3
It is because 1 Joule = Nm
1 N = 1 Pa.m2
1 Joule = Pa.m2. m = Pa. m3
Where,
P is Pascal
N is Newton
m is meter
1 Joule = Ws
1 Watt = Joules/second
1 Joule = Watt x second
Thus, 1 Joule = W.s
Where,
W is the Watt
s is the seconds
1 Joule = C.V
1 Joule = W.s = Watt. Seconds
Watt is the unit of Power
Power = Voltage x Current
Unit of current is Amperes and unit of voltage is volts
1 A = Q/t = charge in coulomb / time in seconds
P = V x Q/t
Converting the above equation in terms of their units, we get:
1 Watt = Volts x Coulomb/seconds
We know that: 1 Watt = Joules/second
Joules/ second = Volts x Coulomb/seconds
J/ s = V x C / s
J = VC
Or
J = CV
Hence, 1 joules = C.V
Other units of heat
The other units of heat are given by:
- Calories
- BTU
Let’s discuss the above two units of heat in detail.
Calories
A calorie is also known as the unit of energy, and it refers to the amount of energy our body burns or the amount of energy it gets from eating or drinking. The calories can be expressed in gram calories or kilocalories.
1 calorie = 4.184 Joules
1 kcal (kilocalories) = 4184 Joules
Or
1 joule = 0.239006 calories
1 joule = 0.000239006 kcal (kilocalories)
BTU
BTU refers to the British Thermal Unit. It is defined as the amount of heat required at the constant pressure to raise the temperature of one pound of the liquid (water) by one degree Fahrenheit. It generally measures the heat content of the fluids, such as fuels.
1 Btu = 1055.06 Joules
1 Btu = 1.05506 kJ (Kilo Joules)
Or
1 Joule = 0.000947817 Btu
1 kJ (Kilo Joules) = 0.947817 Btu
Multiples of Joules
The unit of heat, i.e., Joule, is also expressed in the multiples, which is listed as follows:
| Value | Name (Symbol) |
|---|---|
| 10-1 | Decijoule (dJ) |
| 10-3 | Milijoule (mJ) |
| 10-6 | Microjoule (uJ) |
| 10-9 | Nanojoule (nJ) |
| 10-12 | Picojoule (pJ) |
| 101 | Decajoule (daJ) |
| 103 | Kilojoule (kJ) |
| 106 | Megajoule (MJ) |
| 109 | Gigajoule (GJ) |
| 1012 | Terajoule (TJ) |
What is heat?
Heat is defined as energy, which is transferred from one system to another at different temperatures. The heat generally flows from the high-temperature system to the low-temperature system.
Heat formula
The heat formula is given by:
Where,
C is the specific heat of the body
M is the mass of the body
Q is the heat
T specifies the temperature or the change in temperature
Numerical Examples
Let’s discuss some Numerical Examples on heat.
Example 1: Find the heat required to raise the temperature of the water of mass 0.7 g from 30 degrees Celsius to 90 degrees Celsius?
Solution: The parameters given are:
Change in temperature = 90 – 30 = 60 degrees Celsius.
The specific heat of water is 4186 J/g degrees Celsius
Mass of water be 0.7 g.
The heat formula is given by:
Heat (Q) = 4186 x 60 x 0.7 = 175812 Joules
Heat = 175.812 Kilo Joules
Thus, the heat required to raise the temperature of the water from 30 degrees Celsius to 90 degree Celsius is 175.812 Kilo Joules.
Example 2: Find the specific heat of water mass f 10 kg if the temperature changes from 130 degrees Celsius to 100 degrees Celsius. The heat required is 120 kcal.
Solution: The formula to find the specific heat is given by:
The mass of the water is 10 kg = 10000 g.
Change in temperature is 130 – 100 = 30 degrees Celsius.
Heat (Q) = 120 calories
So, we will first convert the calories into the Joules.
We know that 1 calorie = 4.184 Joules
So, 120 kilo calories = 120 x 4.184 = 502080 Joules
Specific heat (C) = 502080J/10000 g x 30 degrees Celsius
= 1.6736 J/g degree Celsius
Thus, the specific heat of water is 1.6736 J/g degrees Celsius.