Alternating Currents Quiz

An alternating current is one that ...

• changes direction periodically.

• flows in a fixed direction.

• changes only magnitude periodically.

• has a fixed magnitude.

What is meant by rms current?

• steady

  voltage which delivers the same average power as the a.c. to a

  resistive load.

• steady

  current which delivers the same average power as the a.c. to a

  resistive load.

• alternating converted to

  d.c.

• The square root of the mean of the squares of all values of voltage in one full cycle.

The peak current read from an oscilloscope trace is 5.25 A. What is the rms current?

• 7.42 V

• 5.25 A

• 3.71 A

• 2.63 A

The output voltage V of an a.c. power supply varies sinusoidally with time t as shown in Figure. Determine the equation for V in terms of t, where V is in volts and t is in seconds. 

• V = 3.4 sin 2.51 t

• V = 3.4 sin 1.25 t

• V = 1.7 sin 2.51 t

• V = 1.7 sin 5.03 t

Why use AC for electricity supply?

• All of the above

• It can be transformed to high voltages

• It has lower power losses in transmission lines

• It can work equally well with DC

State the type of rectification produced by the circuit shown.

• Half-wave rectification

• Full-wave rectification

What is the process to reduce the range of the output voltage/current, but does not fall to zero?

• Smoothing

• Amplification

• Rectification

• Oscillation

• 240 V

• 250 V

• 170 V

• 340 V

A lamp is connected to a sinusoidal supply. The maximum power transferred by the lamp is 50 W. What is the average power of the lamp.

• 10 W

• 25 W

• 50 W

• 100 W

A bridge rectifier requires at least ____ diode(s).

• 1

• 2

• 4

• 8