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Unit notes and practice questions

Grade 11 Physics unit 5: Heat Conduction and Calorimetry

Everything here is for unit 5 of the Grade 11 Physics textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.

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Practice questions on unit 5
175–216
The textbook pages for unit 5

Short notes for unit 5

The cards filed under this chapter on the Grade 11 Physics page. Open one at a time.

ms cs (Ts−Tf)=mw cw (Tf−Tw)+mk ck (Tf−Tw)m_s\,c_s\,(T_s - T_f) = m_w\,c_w\,(T_f - T_w) + m_k\,c_k\,(T_f - T_w)
msm_s
mass of the hot solid samplekgkg
csc_s
specific heat capacity of the solid (unknown)J kg−1 K−1J\,kg^{-1}\,K^{-1}
TsT_s
initial temperature of the solid°C°C
TfT_f
final equilibrium temperature of the mixture°C°C
mwm_w
mass of the water in the calorimeterkgkg
cwc_w
specific heat capacity of waterJ kg−1 K−1J\,kg^{-1}\,K^{-1}
TwT_w
initial temperature of the water and calorimeter°C°C
mkm_k
mass of the calorimeter and stirrerkgkg
ckc_k
specific heat capacity of the calorimeter materialJ kg−1 K−1J\,kg^{-1}\,K^{-1}

When you use it

Use this when a hot solid is placed in water inside a calorimeter, or a heater warms water in a calorimeter, to find an unknown specific heat capacity.

Watch out

Include the calorimeter and stirrer term whenever their mass is given. Drop it only when the question says to neglect the container.

Drafted from Grade 11 Physics, pages 175-216, then checked twice before it went up

Q=m LQ = m\,L
QQ
heat absorbed or released during the phase changeJJ
mm
mass of the substance changing phasekgkg
LL
latent heat: L_f for fusion or L_v for vaporizationJ kg−1J\,kg^{-1}

When you use it

Use this when a substance melts, freezes, boils or condenses at its fixed transition temperature, such as ice melting at 0 °C or water boiling at 100 °C.

Watch out

The temperature stays constant during a phase change, so do not use mcΔT for that stage. For ice heated from -50 °C, treat heating, melting and heating again as separate steps.

Drafted from Grade 11 Physics, pages 175-216, then checked twice before it went up

ΔL=L0 α ΔT\Delta L = L_0\,\alpha\,\Delta T
ΔL\Delta L
change in lengthmm
L0L_0
original length at the initial temperaturemm
α\alpha
coefficient of linear expansion of the materialK−1K^{-1}
ΔT\Delta T
change in temperatureKK

When you use it

Use this when a rod, wire or track changes length because its temperature changes, for example a steel rail on a hot day or a bridge gap.

Watch out

For area use β = 2α and for volume use γ = 3α. Do not use α directly for area or volume expansion.

Drafted from Grade 11 Physics, pages 175-216, then checked twice before it went up

Practice questions on unit 5

10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.

Question 1

According to physics, what is the definition of heat?

  1. A.The total mechanical energy stored inside an isolated container
  2. B.Energy which is in transit from one body to another as the result of a difference in temperature
  3. C.The quantity of potential energy held by stationary atoms
  4. D.The measure of the total degree of hotness of a single isolated object
Show the answer and why

Answer: B Energy which is in transit from one body to another as the result of a difference in temperature

Why

Heat is defined as energy in transit (in transfer) from one body to another due to a temperature difference between them.

Question 2

Which mechanism of heat transfer occurs via electromagnetic waves and does not require any material medium for transmission?

  1. A.Conduction
  2. B.Convection
  3. C.Radiation
  4. D.Advection
Show the answer and why

Answer: C Radiation

Why

Radiation heat transfer takes place through electromagnetic waves. Unlike conduction and convection, radiation can travel through a vacuum without a material medium.

Question 3

Due to the unusual thermal expansion of water, at what temperature does liquid water have its maximum density?

  1. A.-4 °C
  2. B.0 °C
  3. C.4 °C
  4. D.100 °C
Show the answer and why

Answer: C 4 °C

Why

Between 0 °C and 4 °C, the volume of water decreases as temperature increases. Therefore, water reaches its minimum volume and maximum density at 4 °C.

Question 4

What is the term for a phase change where a substance changes directly from the solid phase into the vapor phase without first becoming a liquid?

  1. A.Sublimation
  2. B.Vaporization
  3. C.Condensation
  4. D.Fusion
Show the answer and why

Answer: A Sublimation

Why

Sublimation is the direct transition of a substance from the solid phase to the vapor phase without passing through the liquid phase.

Question 5

If the linear thermal expansion coefficient of a solid material is α, what is its coefficient of surface (area) expansion β?

  1. A.β = α / 2
  2. B.β = α
  3. C.β = 2α
  4. D.β = 3α
Show the answer and why

Answer: C β = 2α

Why

Area expansion occurs in two dimensions, which gives the relationship β = 2α. (Volume expansion coefficient is γ = 3α).

Question 6

A student in Gondar heats a 0.20 kg block of copper from 20 °C to 70 °C. The specific heat capacity of copper is 385 J/(kg °C). How much heat energy does the copper absorb?

  1. A.1925 J
  2. B.3850 J
  3. C.7700 J
  4. D.15400 J
Show the answer and why

Answer: B 3850 J

Why

Using the heat formula Q = m c ΔT:
Q = (0.20 kg) × (385 J/(kg °C)) × (70 °C - 20 °C)
Q = 0.20 × 385 × 50 = 3850 J.

Question 7

A steel rail segment on a railway line has an initial length of 50.0 m at 10.0 °C. If the temperature rises to 40.0 °C, what is the increase in length of the rail? (Take α for steel = 11 × 10-6 °C-1)

  1. A.0.0055 m
  2. B.0.0165 m
  3. C.0.0330 m
  4. D.0.1650 m
Show the answer and why

Answer: B 0.0165 m

Why

The change in length is given by ΔL = L0 α ΔT.
ΔL = (50.0 m) × (11 × 10-6 °C-1) × (40.0 °C - 10.0 °C)
ΔL = 50.0 × 11 × 10-6 × 30.0 = 0.0165 m.

Question 8

How much heat is required to completely melt 2.0 kg of ice at 0 °C into liquid water at 0 °C? (Take latent heat of fusion of water Lf = 3.33 × 105 J/kg)

  1. A.1.67 × 10^5 J
  2. B.3.33 × 10^5 J
  3. C.6.66 × 10^5 J
  4. D.1.33 × 10^6 J
Show the answer and why

Answer: C 6.66 × 10^5 J

Why

For a phase change without temperature change, Q = m Lf.
Q = (2.0 kg) × (3.33 × 105 J/kg) = 6.66 × 105 J.

Question 9

In a school laboratory in Addis Ababa, an electric heater rated at 200 W operates for 3.0 minutes (180 s) to heat a 0.40 kg block of an unknown metal. The temperature of the block rises from 20.0 °C to 70.0 °C. Assuming all electrical energy is transferred to the block, what is the specific heat capacity of the metal?

  1. A.450 J/(kg °C)
  2. B.900 J/(kg °C)
  3. C.1800 J/(kg °C)
  4. D.3600 J/(kg °C)
Show the answer and why

Answer: C 1800 J/(kg °C)

Why

Total heat supplied is E = P × t = 200 W × 180 s = 36000 J.
Using Q = m c ΔT:
36000 J = (0.40 kg) × c × (70.0 °C - 20.0 °C)
36000 = 20 × c ⇒ c = 36000 / 20 = 1800 J/(kg °C).

Question 10

A 0.05 kg metal bar is heated to 200.0 °C and placed into a container with 0.40 kg of water initially at 20.0 °C. The final equilibrium temperature is 22.4 °C. Neglecting heat absorbed by the container and taking cwater = 4186 J/(kg °C), what is the specific heat capacity of the metal?

  1. A.128 J/(kg °C)
  2. B.385 J/(kg °C)
  3. C.453 J/(kg °C)
  4. D.900 J/(kg °C)
Show the answer and why

Answer: C 453 J/(kg °C)

Why

Using heat conservation: Heat gained by water = Heat lost by metal.
mw cw (Tf - Tc) = ms cs (Th - Tf)
0.40 × 4186 × (22.4 - 20.0) = 0.05 × cs × (200.0 - 22.4)
4018.56 = 8.88 × cs
cs ≈ 453 J/(kg °C).

The app holds 12 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 5

Unit 5 runs from page 175 to page 216 of the Ministry of Education edition.

Ministry of Education edition, English, 338 pages

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All Grade 11 Physics short notes

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