Page 216 - Physics Form 5 KSSM_Neat

Solving Problems Involving Half-Life
LET’S ANSWER
Example 1 LET’S ANSWER

A sample of radioactive material stored in the laboratory has an initial activity
of 480 s . If its half-life is 6 minutes, how much is its activity after 30 minutes?
–1
KEMENTERIAN PENDIDIKAN MALAYSIA
Solution http://bit.
ly/32b5cqV

Step 1: Step 2: Step 3: Step 4:
Identify the Identify the Identify the formula Solve the problem
problem information given that can be used numerically

1 Activity of 4 Number of half-life in 30 min, Info GALLERY
radioactive material, n = t Activity
t = 30 minutes T 1
2 A
= 30 min 0
2 Initial activity of 6 min
radioactive material, = 5 half-life 1
1 n
A = 480 s –1 2 – A 0 A = ( ) A 0
2
0
Half-life, Sample activity after 30 minutes 1 – A
1
5
–1
T 1 = 6 min A = ( ) × 480 s 4 0
2
2 0 Time
= 15 s –1 1 T 2T 1
3 Final activity, – 2 – 2
1
A = ( ) n A 0
2

Example 2

A radioactive material stored in the laboratory has a half-life of 10 days. Calculate the
number of days taken for the activity of a sample of radioactive material to reduce to 25%
of its initial activity.
Solution

T 1 T 1
2 2
100% 50% 25%

Number of days taken = 2 × 10
= 20 days
Therefore, after 20 days, the activity of the remaining radioactive material is 25% of its
initial activity.

206 LS 6.1.4