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CAIE IGCSE Physics 5.2.1.5 Measurements of background radiation

Practise correcting radiation measurements by subtracting background count rate from detector readings, tables or decay graphs.

Syllabus
2026–2028
Course
Physics 0625

Exam points

  • subtract background count rate from a detector reading to find the source count rate
  • interpret a decay graph after background radiation has been removed from plotted values
  • use counts/minute or counts/s consistently when correcting count rate data

5.2.1.5—Measurements of background radiation question 1

[Maximum number: 1]

Some students set up an experiment to measure the count rate for a radioactive source.
First, they measure the radioactive background count rate in the laboratory by taking three measurements. Each measurement is taken over a 10-minute period.

The table shows their results.

Table for Question 5.2.1.5—Measurements of background radiation question 1 — CAIE IGCSE Physics

Next, the students measure the counts near the radioactive source. This count rate is measured as 949 counts per minute.

What is the corrected count rate for the source?

A

932 counts per minute

B

776 counts per minute

C

430 counts per minute

D

78 counts per minute

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