Magnetism and Electromagnetism Set 4

Which effect do loudspeakers make use of to work?

• the Doppler effect

• the generator effect

• the Hall effect

• the motor effect

If an electrical conductor moves relative to a magnetic field, a potential difference is induced across the ends of the conductor. If the conductor is part of a complete circuit, a current is induced in the conductor. What is this effect known as?

• the Doppler effect

• the generator effect

• the Hall effect

• the motor effect

Which of the following can be said about the magnetic field created by an induced current?

• it acts against the change that has made it

• it does not interact with the change that has made it

• it supports the change that has made it

• none of the above

Which of the following factors affect the size of an induced current?

• the number of turns in the coil

• the speed of the movement

• the magnetic field strength

• all of the above

Which type of current is induced by a generator?

• ac in an alternator and dc in a dynamo

• ac in a dynamo and dc in an alternator

• ac in both a dynamo and an alternator

• dc in both a dynamo and an alternator

Which of the following describes how a microphone uses the generator effect?

• it converts a potential difference in a circuit to sound waves

• it converts pressure variations in sound waves to variations in current in an electric circuit

• it converts variations in current in an electric circuit to pressure variations to create sound waves

• it converts variations in sound waves to an electrical current

In transformers, why is iron used for the core in the primary and secondary coils?

• it does not rust

• it is cheap

• it is easily magnetised

• it is light

Which of the following is true about the primary voltage (Vp) and secondary voltage (Vs) in a step-up transformer?

• A. Vp > Vs

• B. Vp = Vs

• C. Vp < Vs

• D. none of the above

There is a potential difference of 100V across a primary coil with 10 turns. The secondary coil has a potential difference of 20V across it. Given that = , how many turns are there in the secondary coil?

• 2

• 5

• 10

• 20

The power output of a transformer is 20W. Given that V_s × I_s = V_p × I_p, what is the voltage across the primary coil if the current through the coil is 5A?

• 2V

• 4V

• 8V

• 10V