Complete Study Material for JEE, NEET, CBSE Board Class 11 Exams
Heat is a form of energy transfer that occurs due to a temperature difference between two objects. It is measured in Joules (J) and plays a crucial role in thermodynamics.
Important Physical Quantities and Their Units Used in Heat
S.N.
Quantity
Unit
Dimension
1
Temperature (T)
Kelvin
[M⁰L⁰T⁰θ¹]
2
Heat (Q)
Joule
[ML²T⁻²]
3
Specific Heat (c)
Joule/kg-K
[M⁰L²T⁻²θ⁻¹]
4
Thermal capacity
Joule/K
[M¹L²T⁻²θ⁻¹]
5
Latent heat (L)
Joule/kg
[M⁰L²T⁻²]
6
Gas constant (R)
Joule/mol-K
[M¹L²T⁻²θ⁻¹]
7
Boltzmann constant (k)
Joule/K
[M¹L²T⁻²θ⁻¹]
8
Coefficient of thermal conductivity (K)
Joule/m-s-K
[M¹L¹T⁻³θ⁻¹]
9
Stefan’s constant (σ)
Watt/m²-K⁴
[M¹L⁰T⁻³θ⁻⁴]
10
Wien’s constant (b)
Meter-K
[M⁰L¹T⁰θ¹]
11
Planck’s constant (h)
Joule-s
[M¹L²T⁻¹]
12
Coefficient of Linear Expansion (α)
Kelvin⁻¹
[M⁰L⁰T⁰θ⁻¹]
13
Mechanical eq. of Heat (J)
Joule/Calorie
[M⁰L⁰T⁰]
14
Vander Waals constant (a)
Newton-m⁴
[ML⁵T⁻²]
15
Vander Waals constant (b)
m³
[M⁰L³T⁰]
** Note : Here θ is used a dimensions of temperature
Question-Answer Format for Class 11 Physics CBSE Board Exam
Q1: What is the difference between heat and temperature?
A: Heat is the total kinetic energy of molecules, whereas temperature measures the average kinetic energy of molecules.
Q2: What is specific heat capacity?
A: The specific heat capacity of a substance is the amount of heat required to raise the temperature of 1 kg of the substance by 1 K.
Q3: Why does metal feel colder than wood at the same temperature?
A: Metal has higher thermal conductivity than wood, so it absorbs heat from our skin faster, making it feel colder.
Do You Know?
The Sun’s surface temperature is about 5,500°C, and it emits heat primarily through radiation.
Water has a high specific heat capacity, making it an excellent coolant.
Black surfaces absorb and emit heat faster than white or shiny surfaces.
Multiple Choice Questions (MCQs) with Answers
Q1: Which of the following has the highest specific heat capacity?
(a) Iron (b) Copper (c) Water (d) Mercury Answer: (c) Water Explanation: Water has a high specific heat capacity, meaning it requires more heat to change its temperature.
Q2: What is the SI unit of heat?
(a) Kelvin (b) Joule (c) Calorie (d) Watt Answer: (b) Joule Explanation: Heat energy is measured in Joules in the SI system.
Worksheet
Define thermal conductivity.
Explain the concept of heat transfer through conduction.
A 500 g piece of iron is heated from 20°C to 80°C. How much heat is required? (Given: Specific heat of iron = 0.45 J/g°C)
Why do we use cooking utensils made of metals?
Test Paper (Total: 20 Marks)
Section A: MCQs (5 × 1 = 5 Marks)
What is the unit of Stefan’s constant?
Define latent heat.
What happens to the temperature of a substance during a phase change?
Which law states that heat energy lost is equal to heat energy gained?
What is the value of the gas constant R in SI units?
6. Differentiate between heat and temperature. 7. Explain why land heats up faster than water. 8. Define thermal capacity and give its unit.
Section C: Numerical Problems (2 × 4 = 8 Marks)
9. Calculate the amount of heat required to raise the temperature of 2 kg of water from 20°C to 60°C. (Specific heat of water = 4.18 J/g°C) 10. A rod expands 2 mm when heated from 25°C to 75°C. If its original length was 1 m, calculate its coefficient of linear expansion.
Section D: Long Answer Question (1 × 3 = 3 Marks)
11. Explain the working principle of a thermos flask with proper diagrams.
Important Points for Quick Revision
Heat is a form of energy transfer due to temperature differences.
SI unit of heat is Joule (J).
Three modes of heat transfer: Conduction, Convection, and Radiation.
Specific heat capacity is the heat required to raise 1 kg of a substance by 1 K.
Latent heat is the heat absorbed or released during a phase change without changing temperature.
Metals are good conductors of heat, while gases are poor conductors.
Heat transfer by radiation does not require a medium.
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