Alternating Current

Question 1

What is the difference between AC and DC current?

Answer 1

AC reverses its direction of flow at periodic intervals while DC does not.

Question 1

What is the single greatest advantage of AC current?

Answer 1

AC can be transformed while DC cannot.

Question 2

What are the three types of AC waveforms?

Answer 2

• Square
• Triangle
• Sine

Question 3

What does a square wave say about the voltage of a circuit?

Answer 3

Voltage is positive for some length of time and then it switches to negative. Voltage will then remain negative for some time before switching back to positive.

Question 4

What does a triangle wave say about voltage?

Answer 4

Voltage rises at a constant rate with respect to time. On a graph, these waves will form straight lines because they are linear.

Question 4

What does a sine wave say about voltage?

Answer 4

Voltage is produced by a rotating machine and there are 360 degrees in one wave. Peak positive voltage is reached at 90 degrees, returns to 0 volts at 180 degrees, increases to negative maximum voltage at 270 degrees, and returns to 0 volts at 360 degrees.

Question 5

Each 360 degree sine wave equals one ______

Answer 5

Cycle

Question 6

The number of complete cycles in one second is called _______. It is measured in _______

Answer 6

Frequency. Hertz

Question 7

The most common frequency in Canada and the US is _______

Answer 7

60 hertz

Question 8

Why are sine waves called sine waves?

Answer 8

They are named that because the voltage at any point along the wavelength is equal to the maximum or peak value times the sine of the angle of rotation.

Question 9

What formula can you use to determine the value at any point along a sine wave?

Answer 9

E(inst) = E(max) X sin <0

E(inst) = The voltage at any point on the waveform

E(max) = The maximum (peak) voltage

Sin <0 = The sine of the angel rotation

Question 10

What is peak value?

Answer 10

The highest value of voltage or current reached by a waveform.

Question 11

What is RMS?

Answer 11

The value of an AC voltage that will produce as much power when connected across a resistor as a like amount of DC voltage.

Question 12

How can the RMS be found?

Answer 12

It can be found by dividing the peak value by the square root of 2 (1.141) or by multiplying the peak value by 0.707 (reciprocal of 1.141).

Question 13

What is the only type for DC circuits?

Answer 13

Resistive

Question 14

What are the three types of loads for AC circuits?

Answer 14

Resistive, inductive, or capacitive.

Question 15

What are resistive loads? What are two characteristics of them?

Answer 15

Loads that contain pure resistance. Two characteristics of them are that they produce heat and the current/voltage are in phase with each other.

Question 16

True power (watts) can be produced only when _________

Answer 16

Both current and voltage are either positive or negative.

Question 17

What is the skin effect?

Answer 17

When electrons are pushed to the outer edges of a conductor because of eddy currents produced by AC. This phenomenon increases the conductor’s resistance.

Question 17

The skin effect is proportional to _________

Answer 17

Frequency