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JAMB Physics Past Questions & Answers - Page 210

1,046.

As a positively charge rod is brought nearer to the top cap of a positively charged gold leaf electroscope, the divergence of the leaves will

decrease to zero

steadily increase

decrease to zero and then increase

remain constant

increase to a maximum and then decrease

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

1,047.

In copper plating, a current of 0.5A is allowed for cathode area of 100cm². If this current is maintained constant for 100 minutes, the thickness of the copper deposited will be approximately (the electrochemical equivalent of copper = 0.0003g/°C, density of copper = 10⁴g/cm³ )

10^-2mm

10^-3mm

10^-4mm

10^-5mm

10^-6mm

View answer & explanation

Correct answer is E

m = Itz

density = $\frac{\text{mass}}{\text{area x thickness}}$

Density = $\frac{Itz}{A \times h}$

$10^4 = \frac{0.5 \times 100 \times 60 \times 0.0003}{100 \times h}$

h = 9 x 10^-7cm = 9 x 10^-6mm

1,048.

If the refractive index of a medium is V2, what is the critical angle?

45^o

50^o12'

56^o25'

75^o

90^o

View answer & explanation

Correct answer is A

sin C = $\frac{1}{n}$ ; sin C = $\frac{1}{√2}$

C = sin^-1 $\frac{1}{√2}$

= 45^o

1,049.

A rod of length 10cm is heated through 100^oC and its final length is 10.26cm. What is the co-efficient of linear expansion of the rod?

0.026 per degree centigrade

0.00026 per degree centigrade

0.26 per degree centigrade

1.0026 per degree centigrade

0.0026 per degree centigrade

View answer & explanation

Correct answer is B

$\alpha$ = $\frac{L_2 - L_1}{L_1 \times \theta}$

= $\frac{10 - 26 - 10}{10 \times 100}$

= 2.6 x 10^-4^oC

1,050.

Why does a piece of cork float on water?

there is no upthrust on it when completely immersed in water

the upthrust on it when completely immersed in water is greater than its weight in air

the upthrust on it when completely immersed in water is less than its weight in air

its specific gravity is greater than that of water

its specific gravity is the same as that of water

View answer & explanation

Correct answer is B

It floats because it weighs more than amount of water it would have to push out of the glass if it sank. This means, its weight in air is less than its upthrust.