AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), June 2025: Question 2

✅ What your diagram must show

• Cell symbol: Long thin line paired with a shorter thicker line ( + | ' - ).
• Ammeter symbol: Circle with capital letter A inside.
• Filament lamp symbol: Circle with an X inside.
• Complete series loop: Continuous wire connecting all three components with no gaps and no extra branches.

🧠 Diagram Description & Marking

Draw a single closed rectangular loop containing:

• The cell on one side.
• The ammeter in series along the line.
• The lamp in series.

❌ Common Errors

• Connecting the ammeter in parallel across the lamp (ammeters must always be in series).
• Leaving wires open or crossing over components without touching terminals.
• Confusing the filament lamp symbol (circle with an X) with the resistor (plain rectangle) or thermistor.

✅ Correct Answer

Tick: Cell

💡 Key Knowledge

The cell stores chemical energy and converts it to electrical energy, providing the potential difference needed to push charge around the circuit. The ammeter only measures current, and the lamp dissipates energy as light and heat.

📐 Step-by-Step Calculation

1. Identify values: Current I = 1.5 A , Time t = 30 s .
2. Use formula: Q = I × t
3. Substitute: Q = 1.5 × 30
4. Final Answer: 45 C

🧠 Exam Technique

• Units are already in standard form (seconds and amperes), so no unit conversions are needed.
• Always write the substitution line 1.5 × 30 to secure the method mark even if you make a calculation slip.

📐 Calculation Steps

1. Values: V = 12 V , I = 1.5 A
2. Substitute into formula:
   R = 12 / 1.5 [1 mark]
3. Calculate value:
   R = 8 (or 8.0) [1 mark]
4. Select unit:
   Ω (ohms) [1 mark]

❌ Common Traps

• Picking the wrong unit: °C is temperature, W (watts) is power, Ω (ohms) is resistance.
• Inverting the division ( 1.5 / 12 = 0.125 ). Remember: R = V / I .

✅ Full-Mark Response

• As the potential difference increases, the current increases. [1 mark]
• The relationship is non-linear (or current increases at a decreasing rate). [1 mark]

🧠 Exam Technique: Two-Part Description

For curved graphs in physics, describing the general trend (both increase) is only worth 1 mark. To get the 2nd mark, you must state how the rate changes:

• Say "non-linear" or "it curves".
• Or say "increases at a decreasing rate" (the curve flattens off).

❌ Major Misconception

Do not say "current is directly proportional to potential difference". A directly proportional relationship produces a straight line through the origin, but this graph curves!

✅ Correct Answer

The resistance increases. [1 mark]

💡 Why does this happen?

As the filament gets hotter, the metal lattice ions vibrate faster and with greater amplitude. This causes more frequent collisions with the flowing electrons (charge carriers), increasing the opposition to current flow (resistance).

📐 Valid Calculations (Pick at least one!)

• Power difference:
  40 W - 8 W = 32 W greater power for filament lamp.
• Power ratio / factor:
  40 W / 8 W = 5 (filament uses 5× more power; LED uses 1/5 the power).
• Brightness per watt:
  LED: 800 / 8 = 100 units/W
  Filament: 800 / 40 = 20 units/W

✅ Model Answer Structure

1. Brightness comparison: Both bulbs produce the exact same brightness (800 arbitrary units).

2. Calculation & Power: The LED bulb only requires 8 W compared to 40 W for the filament lamp. That means the filament lamp uses 32 W more power (or 5 times more power) for the same light output.

3. Advantages / Consequences: Because the LED bulb has a much lower power input, it transfers less electrical energy per second, wastes less energy as heat, costs less money to run, and is significantly more efficient.

🧠 Level 2 Marking Criteria (3–4 Marks)

• Must provide a valid calculation (e.g. 32 W difference or 5× ratio). Without a calculation, you are capped at Level 1 (max 2 marks)!
• Link the lower power input to practical benefits: lower electricity bills / running costs and greater efficiency.
• Note that LED bulbs also last longer / need replacing less often.

❌ Why Students Lost Marks

• Simply copying numbers from Table 1 without doing an actual mathematical calculation.
• Failing to link "lower power" to "less energy used" or "cheaper to run".