A.C. Circuits

A phasor is

• A line which represents the magnitude and phase of an alternating quantity.

• A line representing the magnitude and direction of an alternating quantity

• A colored tag or band for distinction between different phases of a 3-phase supply.

• An instrument used for measuring phases of an unbalanced 3-phase load.

The period of a wave is

• The same as frequency

• Time required to complete one cycle

• Expressed in amperes

• None of the above

The frequency of an alternating current is

• The speed with which the alternator runs

• The number of cycles generated in one minute

• The number of waves passing through a point in one second

• The number of electrons passing through a point in one second

For a frequency of 200 Hz, the time period will be

• 0.05 s

• 0.005 s

• 0.0005 s

• 0.5 s

A sine wave has a frequency of 50 Hz. Its angular frequency is ________ rad/s.

• 100 π

• 50 π

• 25 π

• 5 π

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

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

• None of the above

The equation of 50 Hz current sine wave having r.m.s. value of 60 A is 

• 60 sin 25 t

• 60 sin 50 t

• 84.85 sin 314.16 t

• 42.43 sin 314.16 t

In a capacitance circuit, what is the relationship of voltage and current?

• Current leads voltage

• There is a phase shift

• Voltage leads current

• They are in phase

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

• average voltage

• r.m.s. voltage

• peak voltage

• None of the above

What is the formula to find RMS voltage?

• RMS = Peak / 0.707

• RMS = 0.707 x Peak

• RMS = 0.077 x Peak

• RMS = Peak / 1.414