JAMB Physics Past Questions & Answers - Page 279

1,392.

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

Correct answer is C

half-life = 10 days 

after 10 days, the 4g of element = 2g remaining with 2g disintegrated

after 10 days, 2g of element = 1g left with 1g disintegrated

hence, after 20 days, 3g of the element has been disintegrated with 1g left.

after 10 days, the 1g of element = 0.5g left with 0.5g disintegrated

after 30 days, we have 0.5g of element left with 3.5g disintegrated.

1,393.

When an atom loses or gains a charge, it becomes

A.

an electron

B.

an ion

C.

a neutron

D.

a proton

Correct answer is B

No explanation has been provided for this answer.

1,395.

The electrochemical equivalent of platinum is 5.0 x 10-7kgC-1 to plate-out 1.0kg of platinum, a current of 100A must be passed through an appropriate vessel for

A.

5.6 hours

B.

56 hours

C.

1.4 x 104 hours

D.

2.0 x 104 hours

Correct answer is A

m = Itz

1 = 100 x 5 x 10-7 x t

t = 20,000sec

= 5.6hrs