There are two
kinds of current.
- d.c direct current. This goes in one direction only
- a.c alternating current. This changes
direction several times a second
Mains voltage (230V) changes direction
50 times a second (50Hz)
This s
shaped wave is a sine wave
Frequency is the number of
cycles per second.
e.g. 2 cycles per second
It is measured in
Hertz (Hz). One cycle in one second is 1Hz. Therefore in the
example the frequency is 2Hz
Oscillators
vibrate an exact number of times per second to produce a sine wave of an exact
frequency.
All waves have a frequency
There is such
a huge range of radio frequency (RF) waves that they are sub
divided
Frequency
bands
A group of
frequencies are called a band.
Different people are licensed to
use different bands of frequencies. e.g. aeroplanes, ships, taxis, police,
mobile phones, TV, radio amateurs.
