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JAMB Physics Past Questions & Answers - Page 199

991.

A solid weighs 4.8g in air, 2.8g in water and 3.2g in kerosine. The ratio of density of the solid to that of the kerosine is

$\frac{3}{2}$

$\frac{5}{4}$

View answer & explanation

Correct answer is B

Relative density of solid = $\frac{\text{weight of solid}}{\text{weight of an equal volume of water}}$

$\frac{4.8}{4.8 -3.2}$ = $\frac{4.8}{2}$ = 2.4

Ratio of density of liquid = $\frac{\text{weight of liquid kerosine}}{\text{weight of an equal volume of water}}$

= $\frac{4.8 - 3.2}{4.8 - 2.8}$ = $\frac{1.6}{2}$

= 0.8

= $\frac{\text{density of solid}}{\text{density of kerosine}}$

= $\frac{2.4}{0.8}$ = 3

992.

If I is the current passing through a metallic resistor and H is the rate of Heat generated in the resistor at a constant temperature, then

H $\alpha$ $\frac{1}{I}$

H $\alpha$ $\frac{1}{I^2}$

H $\alpha$ $\sqrt1$

H $\alpha$ I²

none of the above

View answer & explanation

Correct answer is D

H $\alpha$ I²RT

993.

A closed coil of wire is placed near a magnet. The magnet lies along the axis of the coil. Under which of the following conditions would there be no current in the coil?

When the coil is moved toward the stationary magnet

When the coil is moved away from the stationary magnet

when the coil is held stationary but the magnet is moved towards the coil

when both the coil and the magnet are held stationary

when the coil is held stationary but the magnet is moved away from the cell

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

994.

A transformer has 300 turns of wire in the primary coil and 30 turns in the secondary coil.If the input voltage is 100 volts, the output voltage is

5 volts

10 volts

15 volts

20 volts

25 volts

View answer & explanation

Correct answer is B

for transformer,

Es = Ns, Es = e.m.f of secondary

Ep = Np, Ep = e.m.f of primary

NS = number of turns in secondary

Ns = number of turns in primary

$\frac{30}{300}$ = $\frac{x}{100}$

300X = 3000X

= 10 volts