AQA GCSE Physics Physics Paper 1 (Foundation), June 2025: Question 7

📐 Step-by-Step Calculation

1. Identify values: Charge flow Q = 6.0 C , Time t = 12 s
2. Substitute into formula:
   current = 6.0 / 12 [1 mark]
3. Evaluate:
   current = 0.50 A (or 0.5 A) [1 mark]

❌ Common Errors

• Inverting the division: Calculating 12 / 6 = 2 A . Always put charge on top and time on the bottom.
• Missing decimals: Both values had 2 significant figures ( 6.0 and 12 ), so writing 0.50 is ideal practice.

📐 Step-by-Step Calculation

1. Identify values: Charge Q = 6.0 C , Potential difference V = 8.0 V
2. Substitute into formula:
   energy transferred = 6.0 × 8.0 [1 mark]
3. Evaluate:
   energy transferred = 48 J [1 mark]

💡 Key Knowledge

Potential difference (volts) is defined as energy transferred per unit charge ( 1 V = 1 J/C ). Multiplying charge ( C ) by voltage ( V ) always gives energy in joules ( J ).

✅ Correct Answer

Box 3:

efficiency = useful output energy transfer / total input energy transfer [1 mark]

🧠 Exam Technique: Sanity Check

Efficiency compares what you get out to what you put in.

• Useful output can never exceed total input (conservation of energy).
• Therefore, the smaller number (useful output) must always be divided by the larger number (total input).

📐 Step-by-Step Calculation

1. Substitute given numbers into formula:
   0.70 = 1.96 / total input energy transfer [1 mark]
2. Rearrange to solve for input energy:
   total input energy transfer = 1.96 / 0.70 [1 mark]
3. Evaluate:
   total input energy transfer = 2.8 J [1 mark]

❌ Common Errors to Avoid

• Multiplying instead of dividing: Students often calculate 1.96 × 0.70 = 1.37 J .
• Self-check rule: Input energy must always be larger than useful output energy because some energy is always dissipated (wasted as heat and sound). If your answer is less than 1.96 J, you arranged it incorrectly!

✅ Acceptable Answer Range

Any value from 0.74 to 0.78 inclusive [1 mark]

🧠 Exam Technique: How to Extrapolate Curves

• Take a sharp pencil and continue the curve from the last point at (0.5, 0.70) following the existing curvature (it is flattening out).
• Do not draw a sudden straight line or bend it sharply upwards.
• Read up vertically from speed = 0.6 m/s to where your extrapolated curve hits, then read across to the y-axis.

✅ Acceptable Answers (Give either one)

• "The line is curved" (or: not straight / not linear) [1 mark]
• OR: "The line does not pass through the origin" [1 mark]

💡 The Golden Rule of Direct Proportionality

For two quantities to be directly proportional on a graph, two conditions must both be met:

1. The graph must be a straight line.
2. The line must pass directly through (0, 0) / the origin.

Figure 13 fails both conditions, so stating either one earns full credit.