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Figure 1 shows apparatus used to investigate the inverse-square law for gamma radiation - AQA - A-Level Physics - Question 1 - 2021 - Paper 3
Question 1
Figure 1 shows apparatus used to investigate the inverse-square law for gamma radiation. A sealed source that emits gamma radiation is held in a socket attached to ... show full transcript
Worked Solution & Example Answer:Figure 1 shows apparatus used to investigate the inverse-square law for gamma radiation - AQA - A-Level Physics - Question 1 - 2021 - Paper 3
Step 1
Describe a procedure for the student to find the value of d.
Answer
To find the value of d, the student should follow these steps:
- Position a set-square vertically against the edge of the radiation detector, ensuring it makes contact at the top edge of the detector and the base aligns with the bench surface.
- Measure the height at which the top edge of the set-square touches the detector and record this measurement.
- Subtract the height of the bench (138 mm) from the recorded height to determine d.
- Annotate Figure 1 to show the set-square's position, highlighting its contact with the edge of the detector and the base on the bench.
Step 2
Explain whether the values of Rₑ in Questions 01.2 and 01.3 support the student's prediction.
Answer
The student’s prediction can be assessed by comparing the values of Rₑ for the two different distances:
- For d = 530 mm, Rₑ is recorded as approximately 0.3 s⁻¹.
- For d = 380 mm, Rₑ is recorded as 0.76 s⁻¹. Using the inverse-square law, we expect the relationship: rac{Rₑ(380)}{Rₑ(530)} = rac{d^2(530)}{d^2(380)} Substituting the values, we calculate: rac{0.76}{0.3} = rac{530^2}{380^2} If the ratios approximately hold, then the data supports the prediction. The observed increase in count rates is consistent with the inverse-square relationship.
Step 3
Describe a safe procedure to reduce d.
Answer
To safely reduce d, the student should:
- Ensure that the radiation source and detector are both turned off or well-shielded.
- Carefully lower the height of the detector by adjusting the clamp T, ensuring not to exceed any safety limits regarding proximity to the radiation source.
- Maintain a safe distance from the source while making adjustments and use appropriate shielding if available. This procedure is crucial to avoid excessive exposure to gamma radiation.
Step 4
Determine Δd.
Answer
To determine Δd, the student should analyze the incremental changes in d recorded during the experiment, calculating the difference between consecutive d values. If all measured distances follow an equal spacing pattern, then Δd can be identified as the consistent change in these recorded distances, indicating how the distance between the source and the detector has varied.
Step 5
How the student could confirm whether Figure 2 supports the prediction.
Answer
The student can confirm if Figure 2 supports the prediction by analyzing the plotted values of log(Rₑ) against log(d). If the data points approximate a straight line with a slope of -2, then it confirms the prediction Rₑ = k / d² holds true. The closeness of the data points to this line will also indicate the strength of the relationship.