Alternating Current

Using the graph and the equation for alternating current, calculate the value of the current at a time 0.48 s.

• • -16 A

• • -13 A

• 16 A

• 13 A

A heater is rated as 230 V, 10 kW. The value 230 V refers to

• average voltage

• peal voltage

• r.m.s voltage

The r.m.s value of an alternating current is given by steady (D.C) current which when flowing through a given circuit for a given time produces

• the more heat than produced by A.C when flowing through the same circuit

• the less heat than produced by A.C when flowing through the same circuit

• the same heat than produced by A.C when flowing through the same circuit

If a sinusoidal wave has a frequency of 50 Hz with 30 A r.m.s current, which of the following equation represents the wave?

• 42.42 sin 314.2t

• 30 sin 50t

• 60 sin 25t

• 84.84 sin 25t

The period of a wave is

• the same as frequency

• expressed in amperes

• time required to complete one cycle

• none of the above

The mains ac supply in some countries is 110 V r.m.s at 50 Hz (sinusoidal).

What is the peak value of voltage?

• 110 V

• 110 /√ 2 V

• 311 V

• 288 V

What is the ratio of powers delivered by 20 V dc and 20 V peak ac to the same load?

• 20

• 2

• 1

• 0.5

Which will light a lamp more brightly, 12 V peak ac or 12 V steady dc?

• 12 V peak ac

• 12 V steady dc

A current is said to be alternating when it changes in

• magnitude

• 
  direction

• both ‘a’ and ‘b’

• none of these

An oscilloscope shows the current flow above what type of current is it showing?

• DC

• AC

• Rectified Current

• non rectified Current