CIE iGCSE Co-Ordinated Science P5.2.4 Half-life Exam Style Questions Paper 1
▶️ Answer/Explanation
12 hours is 3 half-lives (12 ÷ 4 = 3). After each half-life, the mass halves: 720 g → 360 g → 180 g → 90 g. After 3 half-lives, 90 g remains undecayed.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
The count rate halves each time one half-life passes.
Following the sequence: \(1280 \to 640 \to 320 \to 160 \to 80\), the count rate halves 4 times.
These 4 half-lives take place over the given 20 minutes.
So, one half-life \(= \dfrac{20}{4} = 5.0\) minutes.
✅ Answer: (B)
Following the sequence: \(1280 \to 640 \to 320 \to 160 \to 80\), the count rate halves 4 times.
These 4 half-lives take place over the given 20 minutes.
So, one half-life \(= \dfrac{20}{4} = 5.0\) minutes.
✅ Answer: (B)
▶️ Answer/Explanation
The activity falls from 2000 to 250, which is a factor of 8, i.e. \(2000 \rightarrow 1000 \rightarrow 500 \rightarrow 250\), three halvings.
Three half-lives have therefore passed in the 30 minutes given.
Dividing the total time by the number of half-lives: \(\dfrac{30}{3} = 10\) minutes.
✅ Answer: (B)
Three half-lives have therefore passed in the 30 minutes given.
Dividing the total time by the number of half-lives: \(\dfrac{30}{3} = 10\) minutes.
✅ Answer: (B)
▶️ Answer/Explanation
Half-life is the time taken for the activity of a radioactive substance to fall to half its original value.
Reading the graph, the activity drops from its starting value to half that value over a certain time interval.
This time interval read off the graph is the half-life of the substance.
✅ Answer: (A)
Reading the graph, the activity drops from its starting value to half that value over a certain time interval.
This time interval read off the graph is the half-life of the substance.
✅ Answer: (A)
▶️ Answer/Explanation
A half-life of 4.0 days means the activity halves every 4.0 days going forward, so going backward it doubles every 4.0 days.
8.0 days earlier is exactly \(2\) half-lives before the current time, so \(100 \times 2 \times 2 = 400\) emissions per minute.
This matches option D.
✅ Answer: (D)
8.0 days earlier is exactly \(2\) half-lives before the current time, so \(100 \times 2 \times 2 = 400\) emissions per minute.
This matches option D.
✅ Answer: (D)