The Sine Wave

The sine wave (sinusoidal wave or, simply, sinusoid) is the fundamental form of alternating current (AC) and voltage. The current reverses polarity over time. In one cycle, the polarity changes once. The time required for a given sine wave to complete one full cycle is called a period.
The number of cycles per second is the frequency (f), whose unit is the Hertz (Hz). One hertz is equal to one cycle per second. The frequency and period are reciprocal. More cycles per second results in a higher frequency and a shorter period.

AC Voltage Sources

 

Sine waves are produced electro-magnetically by an AC generator or electronically by an oscillator circuit, which is used in a signal generator.
The figure shows a cross-section of an AC generator. A simplified model of this generator consists of a single loop of wire in a permanent magnetic field. Magnetic flux lines exist around the north and south poles of the magnet. When a conductor rotates through the magnetic field, a voltage is induced.

AC Generator

In a horizontal starting position the loop does not induce a voltage because the conductors are not cutting across the magnetic flux lines. As the loop rotates through the first quarter of the cycle, it cuts through the flux lines producing the maximum induced voltage. During the second quarter of the cycle, the voltage decreases from its positive maximum back to zero. During the second half of revolution, the wire loop cuts through the magnetic field in the opposite direction. Thus, the induced voltage has the opposite polarity. After one complete revolution of the loop, one full cycle of the sinusoidal voltage has been completed.

Signal Generator & Oscilloscope

A signal generator is an instrument that electronically produces sinusoidal voltages or other types of waveforms whose amplitude and frequency can be adjusted. A typical signal generator is shown in the illustration. The oscilloscope is one of the most widely used test instruments. It displays the actual shape of the input voltage as it changes with time. The front-panel view of a typical dual-channel oscilloscope is shown in the diagram.
Please switch on both devices. Change the sine-wave amplitude and frequency. Use the controls on the oscilloscope to improve the display of the waveform. If you need help, use Page Assistance.