Photo AI
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, the vertical distance between the open end of the source and the detector.
Answer
To find the value of d, the student should follow these steps:
- Use a meter ruler to measure the height of the detector from the bench.
- Subtract the known height of the bench (138 mm) from the measurement obtained in step 1, ensuring that the measuring tape or ruler is positioned correctly and perpendicular to the bench to avoid parallax error.
- Add a set-square next to the radiation detector to provide a right angle for accurate reading. Annotate Figure 1 to illustrate this procedure.
Step 2
Explain whether the values of Rₑ in Questions 01.2 and 01.3 support the student’s prediction.
Answer
To determine if the measured values of Rₑ support the prediction, we calculate the ratio of the correction factors:
-
For d = 530 mm:
-
For d = 380 mm:
Evaluating these values, we notice that as d decreases, Rₑ increases, consistent with the predicted relationship Rₑ = k/d². Therefore, the evidence supports the student's prediction.
Step 3
Describe a safe procedure to reduce d. Give a reason for your procedure.
Answer
To safely reduce d, the student should:
- Lower the position of the detector (attached to clamp T) gradually while observing the vertical position to avoid sudden movements that could misalign the setup.
- Consider using a long measuring stick to ensure adjustments are made precisely without needing to disturb the clamp directly. This procedure ensures the distance is minimized while maintaining safety and equipment integrity.
Step 4
Determine ∆d.
Answer
To determine ∆d, the change in distance can be calculated by finding the difference between subsequent d values that the student measures. If the measurements show consistent differences, then we can conclude that ∆d = d_final - d_initial; with clear tabulation of measurements if necessary.
Step 5
How can the student confirm whether Figure 2 supports the prediction?
Answer
The student should analyze the plotted data in Figure 2, checking if a straight line can be drawn with a gradient of -2, which would indicate the inverse square relationship. If the gradient of the best-fit line aligns closely with -2, it confirms the prediction. The student should also compare average values from the data points to ensure consistency and validation of results.
Step 6
Step 7
Explain, with reference to the nature of radioactive decay, why this idea is not correct.
Answer
The assumption that all photons would be detected neglects the probabilistic nature of radioactive decay. Even though 100 gamma photons might enter, they do not arrive at a consistent rate; there are often intervals during which some photons escape detection due to the inherent random nature of decay events. Additionally, the dead time, where photons are not registered, creates a lag in recordings, leading to potential undercounts.