CIE iGCSE Co-Ordinated Science P5.2.4 Half-life Exam Style Questions Paper 1
Question
A radioactive isotope has a half-life of 18 years. A sample contains 80 million atoms of this isotope.
How long does it take for the number of atoms of this isotope in the sample to decrease to 10 million?
A 2.25 years
B 6.0 years
C 54 years
D 180 years
▶️Answer/Explanation
Ans :A
Question
A pure sample of a radioactive substance decays. The graph shows how the number of these radioactive atoms in the sample changes with time.
What is the half-life of the substance?
A 10 s B 20 s C 30 s D 40 s
▶️Answer/Explanation
Ans : A
Question
The isotope of americium used in a smoke detector has a half-life of 430 years. A sample of this
isotope emits 36 000 particles per minute.
At which rate does it emit particles 1290 years later?
A 4500 counts per minute
B 9000 counts per minute
C 12 000 counts per minute
D 18 000 counts per minute
▶️Answer/Explanation
Ans : A
Question
The diagram shows how the count rate for a radioactive isotope varies with time.
How many half-lives of the isotope elapse in 45 hours?
A 1
B 3
C 45
D 75
▶️Answer/Explanation
Ans : B
Question
A radioactive isotope has a half-life of 3.0 days. A sample contains 4000 atoms of this isotope.
How many atoms of the isotope remain after 6.0 days?
(A) 0 (B) 500 (C) 1000 (D) 2000
▶️Answer/Explanation
Ans : C
Question
A radioactive isotope has a half-life of 4.0 days. A sample of the isotope emits radiation at a rateof 100 emissions per minute.
What was the rate of emission from the sample 8.0 days earlier?
(A) 25 emissions per minute
(B) 50 emissions per minute
(C) 200 emissions per minute
(D) 400 emissions per minute
▶️Answer/Explanation
Ans: D
Question
A radioactive sample emits 1280 beta (β)-particles per second.
After 20 minutes, it emits 80 beta (β)-particles per second.
What is the half-life of the radioactive sample?
(A) 4.0 minutes
(B) 5.0 minutes
(C) 10 minutes
(D) 60 minutes
▶Answer/Explanation
Ans : B
Question
The graph shows the decay curve for a radioactive substance.
What is the half-life of this substance?
(A) 2.0 hours
(B) 3.2 hours
(C) 5.0 hours
(D) 10 hours
▶️Answer/Explanation
Ans: A
Question
The graph shows how the rate of emission from a radioactive sample changes with time.
What is the half-life of this sample?
A) 40 minutes
B) 2.0 years
C) 5.0 years
D) 10 years
▶️Answer/Explanation
Answer: B) 2.0 years
Explanation: The half-life is the time taken for the rate of emission to halve. From the graph, the rate decreases from 80 emissions/minute to 40 emissions/minute in 2.0 years, so the half-life is 2.0 years.
Question
The half-life of a radioactive isotope is 8.0 days. How long does it take for the activity to decrease to 1/16 of its original value?
A. 16 days
B. 24 days
C. 32 days
D. 64 days
▶️Answer/Explanation
Answer: C
Explanation: The activity decreases by a factor of 1/16 after 4 half-lives (since 1/16 = (1/2)4). Therefore, the time taken is 4 × 8.0 days = 32 days.