AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), November 2021: Question 5

11 marks · Standard Demand difficulty · Short Answer

Recall and apply electrical equations relating potential difference, current, resistance, power, and energy, and explain the behaviour of a thermistor as temperature changes.

Practise this question

Question

Question text

05 Figure 9 shows a mobile phone with its battery removed.

Figure 9

A student measured the potential difference across the battery and then put the

battery into the phone.

05.1 What is the equation linking current (I), potential difference (V) and resistance (R)?

[1 mark]

Tick ( ) one box.

I = V R

R = I V

V = I R

V = I 2 R

05.2 The current in the electronic circuit in the mobile phone was 0.12 A.

The potential difference across the battery was 3.9 V.

Calculate the resistance of the electronic circuit in the mobile phone.

[3 marks]

Resistance = Ω

05.3 Write down the equation which links energy (E), power (P) and time (t).

[1 mark]

05.4 The battery was fully charged when it was put into the mobile phone.

The battery discharged when the mobile phone was switched on.

The average power output of the battery as it discharged was 0.46 watts.

The time taken to fully discharge the battery was 2500 minutes.

Calculate the energy transferred by the battery.

[3 marks]

Energy transferred = J

The mobile phone includes a sensor to monitor the temperature of the battery.

*24* Figure 10 shows the circuit symbol for a component used in the sensor.

Figure 10

05.5 What component does the circuit symbol shown in Figure 10 represent?

[1 mark]

05.6 The temperature of the component in Figure 10 increases.

The potential difference across the component remains constant.

Explain what happens to the current in the component.

[2 marks]

Mark scheme

Show the mark scheme

AO /

Question Answers Extra information Mark

Spec. Ref.

05.1 V = I R 1 AO1

6.2.1.3

05.2 3.9 = 0.12 × R 1 AO2

6.2.1.3

3.9 1

R =

0.12

R = 32.5 ( ) allow R = 33 ( ) 1

05.3

energy = power × time 1 AO1

6.2.4.2

E = P t

05.4 time = 150 000s 1 AO2

6.2.4.2

energy = 0.46 × 150 000 allow a substitution using an 1

incorrectly/not converted value

of time

energy = 69 000 (J) allow a correct calculation using 1

an incorrectly/not converted

value of time

05.5 thermistor 1 AO1

6.2.1.1

05.6 the current will increase 1 AO1

6.2.1.4

(because) the resistance 1

decreases

Total 11

How to answer it

Electricity in Devices: Circuits, Energy & Sensors

WHAT THIS QUESTION TESTS

This question assesses fundamental electricity and energy concepts from Paper 1:

Formula Recall: Stating the relationships for Ohm's law ( V = I R ) and Electrical Energy ( E = P t ).
Quantitative Skills: Substituting, rearranging equations, and converting time units from minutes to standard seconds.
Circuit Components: Identifying a thermistor from its standard circuit symbol.
Sensor Behaviour: Explaining how temperature changes affect resistance and current in a thermistor circuit.

PART 05.1 • 1 MARK

Equation Linking Current, Potential Difference, and Resistance

Recall of Ohm's Law

✅ Correct Answer

Tick the 3rd box: V = I R

💡 Key Knowledge

Ohm's Law relates potential difference ( V , volts), current ( I , amperes), and resistance ( R , ohms Ω):

V = I × R

❌ Common Errors

Confusing power formulas like P = I² R with Ohm's law.
Misremembering rearrangements like writing I = V R instead of I = V / R .

Mark Scheme: 1 mark for selecting V = I R . No marks if more than one box is ticked.

PART 05.2 • 3 MARKS

Calculating Circuit Resistance

Applying V = I R

📐 Step-by-Step Calculation

Step 1: Substitute known values
3.9 = 0.12 × R [1 mark]

Step 2: Rearrange to make R the subject
R = 3.9 / 0.12 [1 mark]

Step 3: Calculate the final answer
R = 32.5 Ω (or 33 Ω ) [1 mark]

🧠 Exam Technique

Always substitute before rearranging! Even if you make an algebra error when rearranging, substituting correctly first locks in the first method mark.
Double-check units: Current is in Amps (A) and p.d. is in Volts (V), so no prefix conversion was needed here.

❌ Common Errors

Multiplying instead of dividing: calculating 3.9 × 0.12 = 0.468 .
Inverting the division: calculating 0.12 / 3.9 = 0.031 .

Mark Scheme: Substitution [1] • Rearrangement [1] • Final value 32.5 or 33 (Ω) [1]. Full 3 marks awarded for correct unsupported answer.

PART 05.3 • 1 MARK

Equation Linking Energy, Power, and Time

Formula Recall

✅ Correct Answer

energy = power × time

or using symbols: E = P t

💡 Key Knowledge

Power is the rate of energy transfer:

Energy ( E ) in Joules (J)
Power ( P ) in Watts (W)
Time ( t ) in Seconds (s)

🧠 Exam Technique

When asked to "Write down the equation...", you can write it in words or standard specification symbols. Avoid inventing your own letter symbols.

Mark Scheme: 1 mark for energy = power × time or E = P t .

PART 05.4 • 3 MARKS

Calculating Energy Transferred

Unit Conversion & Multiplication

📐 Step-by-Step Calculation

Step 1: Convert time to seconds
Time is given in minutes: 2500 min
t = 2500 × 60 = 150 000 s [1 mark]

Step 2: Substitute into E = P × t
E = 0.46 × 150 000 [1 mark]

Step 3: Calculate energy transferred
E = 69 000 J (or 6.9 × 10⁴ J ) [1 mark]

❌ Common Errors & Trap Alert

Unit Trap: Forgetting to convert minutes to seconds. Students who calculated 0.46 × 2500 = 1150 J lost the conversion mark, scoring a maximum of 2/3.
Dividing by 60 instead of multiplying: calculating 2500 / 60 .

🧠 Examiner Insight

The standard SI unit for time in physics calculations is always seconds. Whenever time is provided in minutes or hours, underline it immediately and convert it first!

Mark Scheme: Conversion to 150 000 s [1] • Substitution of power & time [1] • 69 000 (J) [1]. Allow error carried forward (ecf) for uncoverted time giving 1150 J [2 marks max].

PART 05.5 • 1 MARK

Identifying Circuit Symbols

Recognising the Sensor Component

✅ Correct Answer

thermistor

💡 Key Knowledge

Circuit diagram symbol features:

Thermistor: Resistor rectangle with a line that has a flat "foot" at the bottom (resembling an ice hockey stick). Think: "Hockey stick on ice = cold/temperature → Thermistor".
LDR: Resistor in a circle with arrows pointing inward (light shining in).
Variable Resistor: Resistor with a straight diagonal arrow through it.

❌ Common Errors

Confusing the thermistor with a fuse (a resistor with a straight wire through the middle).
Calling it a "thermal resistor" or "temperature sensor" instead of the exact component name: thermistor.

Mark Scheme: 1 mark for "thermistor". Spelling must be recognisable.

PART 05.6 • 2 MARKS

Explaining Changes in Current

Linking Temperature, Resistance, and Current

✅ Model Answer

1. The current will increase [1 mark]

2. (Because) the resistance decreases [1 mark]

💡 Memory Trick: The TURD Rule

T.U.R.D.

Temperature Up → Resistance Down!

As a thermistor heats up, more charge carriers (free electrons) are released, so resistance drops. Since I = V / R and V is constant, lower resistance causes current to rise.

🧠 Exam Technique

Notice the command word "Explain" for 2 marks:

Mark 1 is for stating what happens (current increases).
Mark 2 is for the physical reason why (resistance decreases).

Always address both the effect and the cause.

Mark Scheme: Current increases [1] • (Because) resistance decreases [1]. Dependent logic: do not award opposite statements.

Topics

Physics · P2: Electricity

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.