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VOOZH | about |
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VOOZH | about |
Unit of Heat is Joule. It is named after the scientist James Prescott Joule in recognition of his contributions to research in thermal sciences. Heat is a form of energy which deals with the body's temperature. Heat energy flows from one body to another due to their temperature difference. Heat is also measured in calories or kilocalories.
In this article, we will learn the definition of heat, its unit in various systems, conversion between different heat units, and some practice problems based on it.
Table of Content
Heat can be defined as follows,
Heat is the thermal energy which is transferred between two systems due to temperature difference in them.
The symbol 'Q' in physics and thermodynamics denotes heat.
The formula to calculate heat is given as follows:
Q = mc ΔT
where,
Q= heat,
m = mass of the body,
c = specific heat, and
ΔT = temperature difference.
Unit of heat is a measure of the amount of thermal energy transferred between two substances due to a temperature difference. It quantifies the amount of heat energy involved in a process. Thus, it is a standard amount of heat chosen for measurement in relation to this quantity.
As heat is calculated by the formula Q = mc ΔT. Hence, one unit of heat can also be defined as amount of heat transferred through a body having mass of 1 kg, specific heat of 1 J/kg-K and a temperature difference of 1 Kelvin.
For convenience, various units of heat have been adopted. The SI unit of Heat is Joule (J).
The dimensional formula for heat is [M1 L2 T-2]. It is derived using the analogy of heat to energy. Energy is equivalent to the work done which is defined as product of Force and displacement, i.e. Work done = Force × Displacement.
Substituting the dimensions of Force and Displacement, we get,
Dimensions of Work Done = [M1L1T-2] × [M0L1T0] = [M1 L2 T-2]
Dimensional Formula of Heat = [M1 L2 T-2]
S.I. Unit of Heat is Joule (J). It is named after the scientist James Prescout Joule. The base unit of heat is same as that of energy and work, i.e. kgms-2.
1 Joule is defined as amount of work done or energy stored in a body if a force of 1 Newton displaces it through 1 meter.
C.G.S. system of units stands for Centimeters (length), Grams (mass), and Seconds (time). In CGS system, the unit of heat is Calorie abbreviated as Cal.
1 Calorie of heat is defined as amount of heat required to raise temperature of 1 gram water by 1 degree celsius. It is found to be approximately equal to 4.2 Joules.
For convenient measurements, the unit kilocalorie (kcal) is used sometimes which is equal to 1000 calories.
Unit is a standard measurement of any physical quantity that is used to express the size or magnitude of any physical quantity. There are different units chosen for the measurement of same physical quantity for its convenient representation in terms of magnitude. The unit of heat in different systems is mentioned below:
Similar to other SI units, the value of Joule can be adjusted to different measures as shown in the table below:
Unit of Heat | Symbol | Equivalent in Joule (J) |
|---|---|---|
Joule | J | 1 |
Millijoule | mJ | 0.001 |
Microjoule | μJ | 0.000001 |
Nanojoule | nJ | 0.000000001 |
Kilojoule | kJ | 1000 |
Megajoule | MJ | 1000000 |
Gigajoule | GJ | 1000000000 |
Unit of heat can be converted from one system to another using the conversion factors given in the following table:
From/To | Joule | Calorie | Kilocalorie | BTU |
|---|---|---|---|---|
Joule |
1 |
0.239006 |
0.000239006 |
0.0009478 |
Calorie |
4.184 |
1 |
0.001 |
0.00396567 |
Kilocalorie |
4184 |
1000 |
1 |
3.96567 |
BTU |
1055.06 |
252.164 |
0.252164 |
1 |
Using the above conversion system we can convert unit of heat from one form to other form.
The difference between heat and temperature is described in tabular form as follows:
Heat | Temperature |
|---|---|
Heat is a form of energy that flows from one system to another due to temperature difference between them. | Temperature is a measure of hotness or coldness of a body or system. |
SI unit of heat is Joule. | SI unit of Temperature is Kelvin. |
Other units of heat include calorie, BTU, etc. | Other units of temperature are Celsius, Fahrenheit, etc. |
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Example 1: Calculate the amount of heat required to raise temperature of 100 grams of water by 20 degree Kelvin. Given that, specific heat of water = 4.2 J/kg-K.
Solution:
We have, Mass of water, m = 100 grams = 0.1 kg
Specific Heat of water, c = 4.2 J/kg-K
Temperature difference, ΔT = 20 K
Also, Heat required, Q = mcΔT
Thus, Q = 0.1 × 4.2 × 20 = 8.4 J
Hence, 8.4 Joules of heat is required for the given case.
Example 2: Convert 120 kcal into SI units.
Solution:
We know that, 1 cal = 4.184 J and 1 kcal = 1000 cal
Thus, 120 kcal = 120 × 1000 cal = 120000 × 4.184 J = 502080 Joules
Hence, the given amount of heat is 502080 J in SI units.
Problem 1: Convert 100 J of heat into calories.
Problem 2: Find the amount of heat required to raise temperature of 200 grams of water by 10 degree Kelvin.
Problem 3: Convert the heat given in SI units as 70 J into CGS units.
Problem 4: 1 kg of water is at 25 degree celsius. What is the amount of heat required to raise temperature of this water to 100 degree celsius?
Problem 5: Convert 1 kcal of heat into SI units.
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