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JAMB Physics Past Questions & Answers - Page 84

416.

A radio station broadcast at a frequency of 600KHZ. If the speed of light in air is 3 × 108ms $^{−1}$ . Calculate the wavelength of the radio wave

2.20 × 10 $^3$ m

5.0 × 10 $^2$ m

5.0 × 10 $^5$ m

11.8 × 10 $^{11}$ m

View answer & explanation

Correct answer is B

V = fλ

λ = $\frac{v}{f}$

= $\frac{3 \times 10^8}{600 \times 10^3}$ = 500m

= 5 × 10²m

N.B 600KHz Frequency = 600 × 10³Hz

417.

A man of mass 50kg ascends a flight of stains 5m high in 5 seconds. If acceleration due to gravity is 10ms $^{-2}$ the power expended is

100w

200w

400w

500w

View answer & explanation

Correct answer is D

Power is the time rate of doing work

i.e power = $\frac{\text{energy}}{\text{time}}$

Since energy = mgH

∴ power = $\frac{mgH}{t}$

= $\frac{50 \times 10 \times 5}{t}$

= 500W

418.

The instrument used to measure the pressure of a gas is

barometer

thermometer

hydrometer

manometer

View answer & explanation

Correct answer is D

Barometer is used to measure atmosphere pressure
Thermometer is used to measure temperature
Hydrometer is used to measure relative density of a liquid
Manometer is used to measure the pressure of a gas

419.

The net capacitance in the circuit above is

80µF

6.0µF

4.0µF

2.0µF

View answer & explanation

Correct answer is D

For capacitance i n parallel, 2µF and 2µF are in parallel,
their equivalence is 2µF and 2µF = 4µF

The 4µF generated is now in series with the remaining 4µF.

The net capacitance for series connection is

$\frac{1}{C}$ = $\frac{1}{4}$ + $\frac{1}{4}$ = 1 + $\frac{1}{4}$ = $\frac{2}{4}$

C = $\frac{4}{2}$

= 2µF

420.

Which of the following operations can be used to convert an alternative current dynamo into a direct current dynamo

number of turns in the coil is increased

strength of the field magnet is increased

slip rings are replaced with split ring commutator

coil is wound on a soft iron armature

View answer & explanation

Correct answer is C

A d.c generator is one in which its current is allowed to flow in one direction even through it may vary in value an a.c generator can only be made to produce a d.c by replacing the two slip rings with a single split ring or commutator