Questions
1. Calculate: Find the heat needed to raise 2 kg of water (c = 4200 J kg⁻¹ °C⁻¹) by 30 °C. Find the unknown using Q = mcθ.
Q = mcθ = 2 × 4200 × 30 = 252000 J = 2.52 × 10⁵ J.
2. Calculate: Find the heat to melt m = 0.5 kg of ice (L = 3.34 × 10⁵ J kg⁻¹). Find the unknown using Q = mL.
Q = mL = 0.5 × 3.34 × 10⁵ = 1.67 × 10⁵ J.
3. Calculate: Gas at p₁ = 1.0 × 10⁵ Pa, V₁ = 2.0 L, T₁ = 300 K is changed to p₂ = 2.0 × 10⁵ Pa, T₂ = 600 K. Find the unknown using p₁V₁ / T₁ = p₂V₂ / T₂.
V₂ = p₁V₁T₂ / (T₁p₂) = (1.0 × 10⁵ × 2.0 × 600) / (300 × 2.0 × 10⁵) = 2.0 L.
4. Calculate: Gas at p₁ = 100 kPa, V₁ = 500 cm³ is compressed to V₂ = 200 cm³ at constant temperature. Find the unknown using p₁V₁ = p₂V₂.
p₂ = p₁V₁ / V₂ = (100 × 500) / 200 = 250 kPa.
5. Calculate: Gas of volume V₁ = 300 cm³ at T₁ = 300 K is heated to T₂ = 400 K at constant pressure. Find the unknown using V₁ / T₁ = V₂ / T₂.
V₂ = V₁T₂ / T₁ = (300 × 400) / 300 = 400 cm³.
6. Calculate: Gas at p₁ = 100 kPa, T₁ = 300 K is heated to T₂ = 450 K at constant volume. Find the unknown using p₁ / T₁ = p₂ / T₂.
p₂ = p₁T₂ / T₁ = (100 × 450) / 300 = 150 kPa.
7. State the manipulated, responding and constant variables for: To determine the specific heat capacity of aluminium by supplying a measured amount of electrical energy and measuring the temperature rise.
Manipulated: Heating time, t. Responding: Temperature of the block, θ. Constant: Mass of the aluminium block and the power of the heater.
8. State the manipulated, responding and constant variables for: To determine the specific latent heat of fusion of ice by melting it with a measured amount of electrical energy, using a control to correct for the surroundings.
Manipulated: Whether the heater is switched on (experiment) or off (control). Responding: Mass of ice melted, m. Constant: Heating time and the power of the heater.
9. State the manipulated, responding and constant variables for: To investigate the relationship between the pressure and the volume of a fixed mass of gas kept at constant temperature.
Manipulated: Pressure of the trapped gas, P. Responding: Volume of the trapped gas, V. Constant: Temperature and the mass of the trapped gas.
10. State the manipulated, responding and constant variables for: To investigate the relationship between the volume and the temperature of a fixed mass of gas kept at constant pressure.
Manipulated: Temperature of the gas, θ. Responding: Length of the trapped air column (proportional to volume), L. Constant: Pressure and the mass of the trapped gas.
11. State the manipulated, responding and constant variables for: To investigate the relationship between the pressure and the temperature of a fixed mass of gas kept at constant volume.
Manipulated: Temperature of the gas, θ. Responding: Pressure of the gas, P. Constant: Volume and the mass of the trapped gas.
12. Explain: why the sea heats up slower than land.
Water has a high specific heat capacity, so it needs a lot of heat to warm up and gives out a lot as it cools. That is why the sea warms and cools more slowly than sand.
13. Explain: why sweating cools you down.
As sweat evaporates it takes latent heat from your skin to turn from liquid to vapour. Losing that heat is what leaves your skin feeling cooler.
14. Explain: why a pressure cooker cooks faster.
Sealing the pot lets pressure build up, and higher pressure raises the boiling point of water. The food then cooks in hotter water and steam, so it is done sooner.
15. Define absolute zero.
The lowest possible temperature, 0 K or about −273.15 °C, at which the particles of a substance have minimum kinetic energy.
16. Define absolute temperature scale.
The temperature scale that begins at absolute zero and is measured in kelvin (K), where a change of 1 K equals a change of 1 °C.
17. Define temperature.
A measure of the degree of hotness of a body, related to the average kinetic energy of its particles; measured in degrees Celsius (°C) or kelvin (K).
18. Define heat.
The energy transferred between bodies because of a difference in temperature; a form of energy measured in joules (J).
19. Define thermal equilibrium.
The state reached when two bodies in contact are at the same temperature, so there is no net transfer of heat between them.
20. Define heat capacity.
The amount of heat needed to raise the temperature of an object by 1 °C (or 1 K); measured in J °C⁻¹ or J K⁻¹.
Marking yourself
- Calculation: formula written, values substituted with units, final answer with unit and sensible significant figures.
- Variables: manipulated = what you change; responding = what you measure; constant = what you keep the same.
- Definition: one sentence, correct physical quantity, correct unit.
Exam tip
More Heat resources
- Chapter overview: Heat
- Revision Notes
- Common Mistakes
- Paper 2 Answering Guide
- Paper 3 Guide
- Key Terms
- Calculation practice sets
Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)