2nd year, Lever1 Lesson11 Comparing Direct Current to Alternating Current
AC is raised from one level of voltage for transmission and then reduced to a different level of voltage for utilization by using ? .
Transformers
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
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
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
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