JAMB Physics Past Questions & Answers - Page 192

956.

A cell has an open circuit voltage V1 and a closed circuit voltage V2 when a current is flowing through it. Therefore, the internal resistance of the cell is

A.

\(\frac{V_2}{I}\)

B.

\(\frac{V_1}{I}\)

C.

\(\frac{(V_1 + V_2)}{I}\)

D.

\(\frac{(V_1 - V_2)}{I}\)

E.

\(\frac{(V_2 - V_1)}{I}\)

Correct answer is E

On open circuit, V1 = I; On closed circuit V2 = IR + Ir

V2 = V1 + Ir

r = \(\frac{(V_2 - V_1)}{I}\)

958.

The ratio of the linear expansivity of copper to that of iron is approximately 1.5. A specimen of iron and a specimen of copper expands by the same amount per unit rise in temperature. The ratio of their length is

A.

3

B.

1.5

C.

1.32

D.

1

E.

0.67

Correct answer is E

\(\alpha_1\)L1 = \(\alpha_2\)L2

\(\frac{L_1}{L_2}\) = \(\frac{\alpha_1}{1.5\alpha_2}\) (since a1- 1.5\(\alpha_2\))


\(\frac{L_1}{L_2}\) = 0.67

959.

A calorimeter of thermal capacity 80j contains 20g of water at 25°C. Water at 100°C is added so that the final temperature of the set-ups is 50°C. The amount of water added is (Heat capacity of water = 4.18J/g/°C)

A.

20g

B.

25g

C.

45g

D.

50g

E.

100g

Correct answer is A

Heat lost = heat gained

mc\(\theta\) = c\(\theta\) + mc\(\theta\)

m x 4.18 x (100 - 50) = 80(50 -25) + [20 x 4.18] x (50 - 25)

m = 20g

960.

Which of the following elements is the best absorber of X-rays?

A.

hydrogen

B.

oxygen

C.

calcium

D.

copper

E.

lead

Correct answer is E

No explanation has been provided for this answer.