AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), 2022: Question 3

10 marks · Standard Demand difficulty · Short Answer

Identify properties of alpha and beta radiation, complete a nuclear equation, and analyze experimental data on count rate versus distance.

Practise this question

Question

A multi-part physics exam question about radioactivity. Figure 4 shows an experimental setup with Americium-241, a radiation detector, and a count rate meter. Questions include selecting the correct nuclear equation for alpha decay, identifying the range of alpha radiation in air, explaining why paper stops alpha radiation, identifying the symbol for a beta particle, calculating a minimum count rate given an uncertainty of 119 ± 7, matching experimental variables (independent, dependent, control) to their descriptions, and describing the relationship shown in a graph of count rate versus distance.
Question text

03 A teacher demonstrated that the radioactive isotope americium-241 emits

alpha particles.

Figure 4 shows the equipment used.

Figure 4

03.1 An americium-241 nucleus (Am) emits an alpha particle and turns into a neptunium

nucleus (Np).

Which is the correct nuclear equation for this decay?

Tick ( ) one box.

[1 mark]

03.2 What is the furthest distance that alpha radiation can travel in air?

Tick ( ) one box.

[1 mark]

A few millimetres

A few centimetres

A few metres 13

03.3 The teacher placed a piece of paper between the americium-241 and the

radiation detector.

The reading on the count rate meter decreased by a large amount.

Why does the decreased reading show that americium-241 emits alpha radiation?

Tick ( ) one box.

[1 mark]

Paper stops alpha radiation.

Paper stops all types of radiation.

Paper stops beta and gamma radiation.

The teacher replaced the americium-241 with a source of beta radiation.

03.4 Which symbol represents a beta particle?

[1 mark]

Tick ( ) one box.

–1e

0e

–1

–1e

–1

e 14

03.5 The count rate from the source was 119 ± 7 counts per second.

Calculate the smallest count rate this could have been.

[1 mark]

Smallest count rate = counts per second

A teacher investigated how the distance between a different radioactive source and

the detector affects the count rate.

03.6 Draw one line from each type of variable to the description.

[3 marks]

Type of variable Description

Count rate

Control variable

Distance between the

source and detector

Dependent variable

Radioactive source

Independent variable

15 Time

03.7 Figure 5 shows how the count rate from the different radioactive source changed with

the distance from the source.

Figure 5

Describe the relationship between the distance from the source and the count rate.

[2 marks]

Mark scheme

Show the mark scheme The mark scheme for question 3. It lists the correct answers: the first nuclear equation box for 03.1; 'a few centimetres' for 03.2; 'paper stops alpha radiation' for 03.3; the first beta symbol box for 03.4; the value 112 for 03.5; a matching diagram for 03.6 linking control to radioactive source, dependent to count rate, and independent to distance; and for 03.7, stating that as distance increases count rate decreases and becomes zero between 40cm and 50cm.

Question 3

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 first box ticked 1 AO2

6.4.2.2

AO /

Spec. Ref.

03.2 a few centimetres 1 AO1

6.4.2.1

AO /

Spec. Ref.

03.3 paper stops alpha radiation 1 AO1

6.4.2.1

AO /

Spec. Ref.

03.4 1 AO1

6.4.2.2

AO /

Spec. Ref.

03.5 112 1 AO2

6.4.2.1

AO /

Spec. Ref.11

03.6 AO3

6.4.2.1

do not accept more than one line from a box on the left

AO /

Spec. Ref.

03.7 as distance increases the count 1 AO3

rate decreases 6.4.2.1

(between 40 cm and 50 cm) the 1

count rate becomes zero

Total Question 3 10

How to answer it

Radioactive Decay and Properties of Radiation

What this question tests

This question assesses your ability to identify nuclear equations, recall the physical properties (range and penetration) of alpha and beta radiation, calculate uncertainty, and identify experimental variables from a graph.

Part 03.1

Alpha Decay Equations

Correct Answer

The first box:
²⁴¹₉₅Am → ²³⁷₉₃Np + ⁴₂He

Key Knowledge

  • An alpha particle is a Helium nucleus (⁴₂He).
  • In alpha decay, the mass number (top) decreases by 4.
  • The atomic number (bottom) decreases by 2.

Exam Technique

Treat the arrow like an equals sign. The numbers on the left must equal the sum of the numbers on the right.
Top: 241 = 237 + 4 (Correct)
Bottom: 95 = 93 + 2 (Correct)

Parts 03.2 & 03.3

Alpha Radiation Properties

Correct Answers

  • 03.2: A few centimetres
  • 03.3: Paper stops alpha radiation

Key Knowledge

Alpha particles are large and highly ionising, which means they bump into air molecules easily. This makes them weakly penetrating.

Common Errors

Don't confuse Alpha with Beta! Beta travels "a few metres" and requires aluminium to stop it. Gamma travels "many metres" and requires thick lead.

Part 03.4

Beta Particle Symbol

Correct Answer

The first box: ⁰₋₁e

Key Knowledge

A beta particle is a high-speed electron emitted from the nucleus. It has virtually no mass (0) and a charge of -1.

Part 03.5

Calculating Uncertainty

Step-by-Step Calculation

  1. Identify the mean value: 119
  2. Identify the uncertainty range: ± 7
  3. To find the smallest possible value, subtract the uncertainty:
    119 - 7 = 112

Final Answer: 112 counts per second

Part 03.6

Experimental Variables

Correct Matching

  • Independent: Distance between source and detector
  • Dependent: Count rate
  • Control: Radioactive source

Tutor Tip

The Independent variable is the one you change (the x-axis). The Dependent variable is the one you measure (the y-axis). Control variables must stay the same to make it a fair test.

Part 03.7

Interpreting the Graph

Correct Answer (2 Marks)

1. As distance increases, the count rate decreases. (1 mark)
2. The count rate becomes zero between 40 cm and 50 cm. (1 mark)

Examiner Commentary

To get full marks on "describe the relationship" questions, always state the general trend first. Then, look for a specific feature on the graph, such as where the line hits the axis or a specific value where the trend changes.

Visualising the Graph

The graph shows a curve that starts high (60 counts/s at 5 cm) and drops rapidly. By the time the distance reaches 45 cm, the line has touched the bottom axis (0 counts/s). This confirms the "short range" property of the radiation being tested.

Topics

Physics · P4: Atomic Structure

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.