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WAEC Physics Past Questions & Answers - Page 156

776.

an electric motor is a machine that converts

A.

mechanical energy into electrical energy

B.

electrical energy into mechanical energy

C.

high voltage to low voltage

D.

low voltage to high voltage

Correct answer is B

No explanation has been provided for this answer.

777.

A bar magnet is placed near and lying along the axis of a solenoid connected to a galvanometer. The pointer of the galvanometer shows no deflection when

A.

the magnet is moved away from the stationary solenoid

B.

the solenoid is moved away from the stationary magnet

C.

the magnet is moved towards the stationary solenoid

D.

there is no relative motion between the magnet and the solenoid

Correct answer is D

No explanation has been provided for this answer.

778.

Lenz's law of electromagnetic induction states that

A.

a force is exerted on a current-carrying conductor in a magnetic field

B.

electromotive force id induced in a circuit whenever there is a change in the magnetic flux linked with the circuit

C.

the magnitude of the induced electromotive force in a circuit is proportional to the rate of change of flux linking the circuit

D.

the induced current in a coil is in such a direction that it sets up a magnetic field which opposes the change producing it

Correct answer is D

No explanation has been provided for this answer.

780.

A constantan wire has a cross sectional area of 4 x 10-8m2 and a resistivity of 1.1 x 10-6Ωm. If a resistor of resistance 11Ω is to be made from this wire, calculate the length of the wire required

A.

0.4m

B.

0.8m

C.

2.5m

D.

5.0m

Correct answer is A

L = RAe=11×4×1081.1×104=0.4m