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CodeVID-P11-10-HTR-01
Heat Transfer — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The SI unit of thermal conductivity is:
- A.$\text{W}\,\text{m}^{-1}\,\text{K}^{-1}$
- B.$\text{W}\,\text{m}\,\text{K}$
- C.$\text{J}\,\text{kg}^{-1}\,\text{K}^{-1}$
- D.$\text{W}\,\text{m}^{-2}\,\text{K}^{-4}$
2.
Sea and land breezes are an example of heat transfer by:
- A.conduction
- B.convection
- C.radiation
- D.evaporation
3.
A perfect absorber and emitter of radiation is called a:
- A.grey body
- B.white body
- C.black body
- D.shiny body
4.
Stefan's constant $\sigma$ has the value:
- A.$6.67\times10^{-11}$
- B.$5.67\times10^{-8}\ \text{W}\,\text{m}^{-2}\,\text{K}^{-4}$
- C.$1.38\times10^{-23}$
- D.$3\times10^{8}$
5.
Wien's displacement law connects temperature with the:
- A.total energy radiated
- B.wavelength of maximum emission
- C.speed of radiation
- D.thermal conductivity
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Distinguish between conduction and convection.
7.
Why is radiation the only mode of heat transfer through a vacuum?
8.
State Newton's law of cooling.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
A slab of area $2\ \text{m}^2$ and thickness 0.1 m has faces at $40\,^\circ$C and $20\,^\circ$C. Find the rate of heat flow. ($k=0.8\ \text{W}\,\text{m}^{-1}\,\text{K}^{-1}$)
10.
State the Stefan–Boltzmann law and use it to find how the radiated power changes when the absolute temperature is tripled.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the three modes of heat transfer with one everyday example of each, and state the law governing conduction and the law governing black-body radiation.
Answer Key
Section A — Multiple Choice Questions
- (A) $\text{W}\,\text{m}^{-1}\,\text{K}^{-1}$
- (B) convection
- (C) black body
- (B) $5.67\times10^{-8}\ \text{W}\,\text{m}^{-2}\,\text{K}^{-4}$
- (B) wavelength of maximum emission
Section B — Short Answer (2 marks)
- In conduction heat passes molecule to molecule with no bulk movement (mainly in solids); in convection the heated fluid itself moves, carrying heat with it.
- Radiation travels as electromagnetic waves which need no medium, whereas conduction and convection both require matter.
- The rate of loss of heat of a body is proportional to the temperature difference between the body and its surroundings, for a small difference.
Section C — Short Answer (3 marks)
- $\frac{Q}{t}=\frac{0.8\times2\times20}{0.1}=320\ \text{W}$.
- $E=\sigma T^4$; tripling $T$ gives $(3)^4=81$, so the radiated power becomes 81 times the original.
Section D — Long Answer (5 marks)
- Conduction: heat passes through a solid molecule to molecule (a metal spoon heating in hot soup), governed by $\frac{Q}{t}=\frac{kA\,\Delta T}{L}$. Convection: a heated fluid rises and circulates (boiling water in a pan, sea breezes). Radiation: heat travels as EM waves through vacuum (the Sun warming the Earth), with a black body radiating $E=\sigma T^4$ by the Stefan–Boltzmann law.
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