Chapter 3: Electric Current

DC Voltage

- Fixed polarity - Can be steady or vary in magnitude. - Steady value cannot be stepped up or down by a transformer. - Measured by DC Voltmeter

AC Voltage

- Reverses in polarity - Varies between reversals in polarity. - Can be stepped up or down by a transformer for electric power distribution. - Difficult to measure because it varies with time. - Measured by AC Voltmeter - Meter reads the root- mean square of AC voltage.

Cycle

- The change in direction from forward to backward to forward again. - One complete alternation is called a cycle

Electric Current

1. Alternating Current (AC) 2. Direct Current (DC)

Triangular Waveform

A bi-directional non-sinusoidal wave that oscillate between a positive and a negative peak value.

Waveform

A representation of how AC varies with time. - Most familiar AC waveform is the sine wave, in which the current or voltage varies with the sine of elapsed time.

Mains Waveform

A sine wave and one which constantly alternates between a maximum and minimum value over time.

Square-Wave Waveform

A symmetrical in shape and has a positive pulse width equal to its negative pulse width resulting in a 50% duty cycle. - Used extensively in electronic and micro-electronic circuits for clock and timing control signals.

Alternating Current (AC)

An electrical current whose magnitude and direction vary cyclically, as opposed to direct current or continuous current, whose direction remains constant. - Movement of electric charge periodically reverses direction with time. - The usual waveform of an AC power circuit is a sine wave (continuous wave), as these result in the most efficient transmission of energy. - AC is the form in which electric power is delivered to businesses and residences.

Conventional Current vs. Electron Current

Direction of conventional current is in the direction in which positive charge flows. - In gases and liquids both positive and negative ions move. - Only negative charge that is electron, move through solids and this is referred to as electron current. - Conventional current is used in referring to the direction of electric charge flow. - Conventional current from (+) to (-) is equal to a negative (electron) current from (-) to (+).

Electric Current

Exists whenever electric charge flows through a region.

DC Voltage has a _________ polarity

Fixed

Which of the following gives the unit of frequency?

Hertz (Hz)

Frequency

Number of cycles per second. Unit of frequency is Hertz (Hz).

Sawtooth Waveform

Periodic waveform; having an amplitude that varies linearly with time between two values, the interval in one direction often being much greater than the other.

AC mains waveform supply at our home is:

Sine Wave

Amplitude

The magnitude or intensity of the signal waveform measured in volts or amps.

Rectangular Waveform

The two pulse widths of the waveform are of an unequal time period. Rectangular waveforms are therefore classed as "Non-symmetrical" waveforms.

Period

Time taken for one cycle; measured in seconds f=1/T

DC Is the _________ flow of electric charge

Unidirectional

Direct Current (DC)

Unidirectional flow of electric charge - Produced by electro-chemical and photo-voltaic cells and batteries.