AC Principles

How do you convert radians to degrees?

multiply by 180/π e.g. 2 radians = 2 x π/180 = 114.59°

How do you convert degrees to radians?

multiply by π/180 e.g. 45° = 45 x π/180 = 0.79 radians.

What are the 4 type of wave shapes?

Square, Triangular, Sawtooth, Pulse

What are harmonics?

multiples of the fundamental frequency

Describe the definition of "RMS"

"Root Mean Square" is the value of AC that gives the same heating effect as an unvarying DC. RMS Value = 70.7% max value (sine wave only) or Max/√2

Describe the definition of "average value"

63.7% of Max (sine wave only) or 2/π x Max value

What is a vector?

A line representing the magnitude and direction of a quantity.

What is a phasor?

An illustration of the generation of a sine wave which represents instantaneous values with respect to time.

Describe the definition, unit and symbol for "frequency"

Frequency is the number of complete cycles that occur in one second. Unit: Hertz Symbol: f

Outline the effect of combining AC and DC voltages.

If the DC voltage is greater than the AC peak voltage, the combined voltage will produce a sine wave that never reverses polarity. Instead the sine wave will sit on the DC level.

How can the angle between any two phasors be expressed?

In radians or degrees

Define AC

Pure AC is a current or voltage that is constantly changing in magnitude and periodically changing in direction.

What is the leading edge?

The first step or transition of a pulse from one level to another.

What is the fundamental frequency?

The frequency of a complex wave

Describe the definition, unit and symbol for "peak value"

The maximum obtainable value which a waveform reaches above or below a reference level.

Define angular velocity, unit and symbol.

The measure of speed of rotation of an object. Unit: radians/second Symbol: ω

What is pulse repetition frequency?

The number of times that a pulse occurs in one second

Describe the definition, unit and symbol for "wavelength"

The physical distance in metres between two corresponding points of a cycle. Unit: Metres Symbol: λ

What is the rising edge?

The positive going transition of a pulse

What is the mark to space ratio?

The ratio of ON time to OFF time.

What is the duty cycle?

The ratio pulse width to period.

What is the trailing edge?

The second step or transition of a pulse from one level to another.

Describe the definition, unit and symbol for "period"

The the taken to generate one complete cycle of an AC waveform. Unit: Seconds Symbol: T

What is the rise and fall time?

The time taken for the waveform to change from one level to another.

What is the pulse repetition time?

The time taken to complete one cycle. PRT is the inverse of the PRF

Describe Phase Angle in terms of degrees

There are 360 degrees in a complete circle

What is a phase shift?

When a sine wave is moved left or right with respect to the reference line.

What does in phase mean?

When two values reach their peak at the same time and they pass through zero at the same time.

What is pulse width?

the time the pulse is present. e.g the width of the pulse.