2nd year, Lever1 Lesson11 Comparing Direct Current to Alternating Current

The measure of the number of cycles per second of the voltage produced by an AC generator is called the frequency of that voltage and is measured in ? .

Hertz

? voltages are better for transmitting electricity over long distances.

Higher

Sine waves are so named because the voltage at any point along the waveform is equal to the maximum (peak) value ? the sine of the angle of rotation.

Multiplied by

AC is raised from one level of voltage for transmission and then reduced to a different level of voltage for utilization by using ? .

Transformers

In a direct current (DC) circuit, current flows in the same direction, but in an alternating (AC) circuit, current changes direction periodically.

True

The power loss (I2R) of a transmission line can be reduced by either decreasing the resistance of the wire or decreasing the amount of current.

True

When attempting to lower power loss by reducing current, ? must be raised by the same proportion to deliver the same amount of power to the user.

Voltage

The four forms of measurement of voltage and current associated with sine waves are peak, peak-to-peak, rms, and ? .

average

Skin effect is greater at high ? .

Frequencies

At how many points along a complete (360°) sine wave will the voltage be equal to zero?

3

The most common frequency in North America is ? .

60 Hz

What is the frequency of a waveform that has gone through 60 cycles in one second?

60 Hz

At what point is the voltage on a sine wave maximum positive?

90°

Each complete revolution (360° travel) of the loop of wire in an AC generator is called a(n) ? .

Cycle

Each time the voltage reverses polarity, the current flow through the circuit changes ? .

Direction

Reducing the resistance of the wire by one-half will reduce power loss to 25%, but reducing the current by one-half will reduce the power loss to 50%.

False

An AC voltage that will produce the same amount of power as a like value of DC voltage is called the ? value.

RMS

Another name for the effective value is the ? value.

RMS

Skin effect increases the effective ? of the conductor.

Resistance

The AC voltage waveform is in the positive direction for some period of time, and in the negative direction for some period of time. The name given to this waveform is the ? wave.

Sine

The tendency of AC current to flow near the surface of a conductor and not evenly throughout the conductor is called ? effect.

Skin

Using higher voltages to transmit electricity allows the use of ? wire.

Smaller

The biggest single advantage of AC is that it can be ? from one voltage to another.

Transformed