Chap 18: Alternating Current

Question 1

Direct current (d.c.) circuit

Answer 1

Circuit where the direction of its current or polarity of voltage remains constant.

Example: A battery-powered flashlight operates on a direct current circuit.

Question 2

Alternating current (a.c.) circuit

Answer 2

Circuit where the direction of its current or polarity of voltage varies periodically with time.

Example: Most household electrical systems operate on alternating current circuits.

Question 3

Period

Answer 3

Time taken for the current (or voltage) to complete one cycle.

Frequency is the reciprocal of the period.

Question 4

Frequency

Answer 4

Number of times the current passes through its zero value in the same direction in unit time.

Example: A frequency of 60 Hz means the current changes direction 60 times per second.

Question 5

Peak value

Answer 5

Maximum value of the current (or voltage) in either direction of the zero value in a periodic cycle.

Peak-to-peak value is double the peak value.

Question 6

Root-mean-square (r.m.s.) value of an alternating current (or voltage)

Answer 6

Value of alternating current (or voltage) that is equal to the steady direct current (or voltage) which would dissipate heat at the same average rate in a given resistor.

The r.m.s. value is calculated using the formula: V_rms = V_peak / √2.