Electrical Fundamentals 3b

Moving a permanent magnet through a coil of wire will

• demagnetize the magnet

• the wire will become an electromagnet

• the magnet will become electrified

• a current will be generated in the wire

Electric currents passing through wires will produce a(n)

• solenoid

• magnet

• magnetic field

• insulator

An inductor of inductance 22.0 mH is connected to an a.c. supply with frequency f. If the reactance of the inductor is 660 Ω, what is the value of f?

• 3.00undefined Hz

• 4.77undefined Hz

• 7.16undefined Hz

The variation of voltage across an inductor with time t in an a.c. circuit is as shown in the graph. Which graphs shows the variation of the current I which flows through the inductor with time t?

• 
• 
• 
• 

A Capacitor blocks

• Only a.c.

• Only d.c.

• Both ac and dc

• None of these

What happens at resonance?

• Current is maximum

• Impedance is maximum

• Resistance is maximum

• Power factor is maximum

The function of a generator is to change ____. 

• mechanical energy to electrical energy
• electrical energy to mechanical energy 
• electrical energy to chemical energy
• chemical energy to electrical energy 

If the frequency of the AC voltage across an inductor is doubled, the inductive reactance of that inductor

• increases to 4 times its original value.

• increases to twice its original value.

• decreases to one-half its original value.

• decreases to one-fourth its original value.

A pure inductor is connected to an AC power supply. In this circuit, the current

• leads the voltage by 90°.

• lags the voltage by 90°.

• is in phase with the voltage.

• none of the given answers.

A resistor is connected to an AC power supply. On this circuit, the current

• leads the voltage by 90°.

• lags the voltage by 90°.

• is in phase with the voltage.

• none of the given answers