Half-life and decay constant - Jamb Physics Past Questions and Answers

Question 1:

• JAMB 1979

Which of the following is the correct definition of 'half-life'?

A. The average life-time of a radioactive material
B. The time it takes a radioactive material to decay to half of its original quantity
C. Half the period a radioactive material decays completely
D. Half of the decay constant
E. The decay constant times life-time

Question 2:

• JAMB 1991

4g of a radioactive material of half-life 10 days is spilled on a laboratory floor. How long would it take to disintegrate 3.5g of the material?

A. 1\(\frac{1}{4}\) days
B. 8\(\frac{1}{4}\) days
C. 30 days
D. 80 days

Question 3:

• JAMB 1992

After three half lifes, the fraction of a radioactive material that has decayed is

A. \(\frac{1}{8}\)
B. \(\frac{1}{3}\)
C. \(\frac{2}{3}\)
D. \(\frac{7}{8}\)

Question 4:

• JAMB 2020

A substance has half of 3 min. After 6 min, the count rate was observed to be 400. What was its count rate at zero time?

A. 1600
B. 1200
C. 200
D. 2400

Question 5:

• JAMB 2021

If the fraction of the atoms of a radioactive material left after 120 years is 1/64, what is the half-life of the material?

A. 24 years
B. 20 years
C. 10 years
D. 2 years