AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), November 2021: Question 4

✅ Correct Answers

04.1: 300 W/m²

04.2: Any of the following:

• (Cities closer to the equator) receive a greater solar intensity.
• They receive more radiation / energy from the Sun.

🧠 Exam Technique & Graph Reading

For 04.1: Locate 4200 km on the x-axis (one small square = 200 km, so move 1 square right from 4000 km). Trace up to the curve and read horizontally across to exactly 300 W/m².

For 04.2: Always use scientific vocabulary given in the question stem (e.g. solar intensity or radiation).

❌ Common Errors (Examiner Warning)

• Vague non-scientific phrases: Writing "they get more sunshine" or "it is hotter there" gets 0 marks. Examiners look for the term radiation, intensity, or energy.
• Misreading the scale: Counting squares incorrectly on the x-axis. Always double-check grid intervals.

✅ Correct Answer

Burning fossil fuels contributes to global warming because there is an increase in the amount of carbon dioxide in the atmosphere.

💡 Key Knowledge

Fossil fuels are hydrocarbons. Complete combustion reacts carbon with oxygen to form carbon dioxide (CO₂), a primary greenhouse gas that absorbs infrared radiation and causes global warming.

📐 Step-by-Step Calculation (04.4)

Equation: useful power output = efficiency × total power input

1 Substitute values directly into equation:

useful power = 0.61 × 1100

2 Calculate final output:

useful power output = 671 W (allow 670 W)

✅ Correct Answer (04.5)

Suggest how panel size affects input power:

Larger heating panels have a greater input power (or absorb more solar energy per second).

💡 Key Knowledge: Surface Area & Power

Solar radiation arrives with a fixed intensity in W/m² (Watts per square metre). Increasing the surface area (panel size) intercepts more radiation per second, thus directly increasing input power.

✅ Correct Selection

☑ The energy required to increase the temperature of 1 kg of water by 1 °C.

❌ Common Errors & Distractors

• Confusing energy with power: Two options deliberately used the word power (rate of energy transfer in Watts). Specific heat capacity is measured in Joules (energy).
• Confusing with Latent Heat: The options discussing a "change of state from liquid to gas" describe specific latent heat of vaporisation, not specific heat capacity.

📐 Step-by-Step Calculation

Formula: ΔE = m × c × Δθ

• 1 Identify and list given values:
  Thermal energy ( ΔE ) = 8 400 000 J
  Mass ( m ) = 80 kg
  Specific heat capacity ( c ) = 4200 J/kg °C
• 2 Substitute values into formula:
  8 400 000 = 80 × 4200 × Δθ [1 mark]
• 3 Rearrange to make Δθ the subject:
  Δθ = 8 400 000 / (80 × 4200)
  Δθ = 8 400 000 / 336 000 [1 mark]
• 4 Calculate final answer:
  Δθ = 25 °C [1 mark]

❌ Common Calculation Traps

• Order of operations error: Typing 8400000 ÷ 80 × 4200 into a calculator without brackets. This computes (8400000 / 80) × 4200 = 441 000 000 ! Always multiply the denominator terms first: (80 × 4200) = 336 000 .
• Unit conversion check: No unit conversions were needed here (kg, J, and J/kg °C matched), but always check for kJ or grams.

✅ Correct Answers

04.8: ☑ Thermal insulation decreases the rate of energy transfer.

04.9: ☑ B (Material B has a thermal conductivity of 2 arbitrary units)

💡 Key Knowledge: Thermal Conductivity Rule

Thermal conductivity measures how rapidly heat energy travels through a material via conduction.

• High thermal conductivity: Fast heat transfer (good conductor, e.g. Material C = 8).
• Low thermal conductivity: Slow heat transfer (good insulator, e.g. Material B = 2).

❌ Common Misconception

Students frequently select the highest number (Material C) thinking "higher number = better material". Always remember: the best insulator has the lowest thermal conductivity.