Progress Test 4 Single-phase alternating current

Identify the feature of the waveform labelled Z.

• amplitude

• form factor

• frequency

• time period

Answer explanation

Amplitude is the measurement from the equilibrium line to the peak of the waveform.

On the waveform shown, draw a line to indicate the RMS value.

Answer explanation

The RMS is roughly 70% of the peak amplitude.

What is the shape of the waveform displayed on the oscilloscope?

Answer explanation

This is a Sine waveform

Calculate the periodic time in seconds of a sine wave which has a frequency of 50Hz.

Mathematical Equivalence

OFF

Answer explanation

time = 1/frequency

time= 1/50

time = 0.02s

If the periodic time of a waveform is 0.25s, what is its frequency?

Mathematical Equivalence

ON

Answer explanation

frequency = 1/time

frequency = 1/0.25

frequency = 4Hz

What is the purpose of a rectifier circuit?

Answer explanation

A rectifier is an electrical device used to convert alternating current (AC) into direct current (DC) by allowing a current to flow through the device in one direction only. Diodes work like one-way valves within the rectifier to maintain this flow of current. This process is generally known as “rectification.”

Draw a full wave rectifier circuit. Showing input and output waveforms.

Answer explanation

The circuit of the full wave rectifier can be constructed in two ways. The first method (image on the left) uses a centre tapped transformer and two diodes. This arrangement is known as a centre tapped rectifier. The second method (image on the right) uses a standard transformer with four diodes arranged as a bridge rectifier.

Examine the circuit and calculate the value of the resistor.

Answer explanation

R = Vs-Vf/If

R = 5-3/0.020

R = 2/0.020

R = 100 Ohms