2017 - JAMB Physics Past Questions and Answers - page 3

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.

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

Barometer is used to measure atmosphere pressure

Thermometer is used to measure temperature

Hygrometer is used to measure relative density of a liquid

Manometer is used to measure the pressure of a gas

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

V = fλ

λ = (\frac{v}{f})

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

= 5 × 10²m

N.B 600KHz Frequency = 600 × 10³Hz

Scalar quantity is a quantity with only magnitude, it has no direction

Tension, weight, impulse are vector quantities because they have direction. Mass is the only scalar quantity there

Power of a lens = (\frac{1}{f})

f = focal length

f = (\frac{1}{p})

= (\frac{1}{5})

= 0.2m

From Hoke's Law, F = ke, K = Constant of Force

For he first case, Force = mg,

= 0.8 × 10 = 8N

∴ 8 = k × 0.04

k = (\frac{8}{0.04})

= (\frac{200N}{m})

Since K is constant

For the second case, F = ke

F = 200 × e

∴ e = (\frac{F}{200})

= (\frac{16}{200})

= 0.08m

Eddy currents are produced by the varying flux cathode, the iron core of an equipment thus reducing efficiency due to power consumption. It can be reduced by laminating the core by breaking up the path of eddy current or by increasing the resistance of the core

Usage of insulated soft iron wire is to reduce hysteresis loss

Usage of low resistance wire (thick wire) is to reduce I2R loss

Usage of thick wire is to reduce leakage heat loss due to leakage of magnetic flux

Thus the correct answer is to use high resistance wire or thin wire

c = 8µF, v = 10v

Energy stored = (\frac{1}{2}) cv²

= (\frac{1}{2}) × (8 × 10− 6) × 10²

= 4 × 10(^{-4})