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?
Section B: Short Answer Questions (3 × 2 = 6 Marks)
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.
Test Your Knowledge (Quiz)
Heat Quiz
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Written by: Neeraj Anand
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