Looking at Electricity

There are two forms of electrical flow:

a.c. - __________ current
d.c. - __________ current

In alternating current the flow of electrons changes __________. First they flow one way and then the other. With UK mains electricity (which is a.c.) the flow changes direction 50 times a second. The units __________ (Hz) are for frequency, which means "per second". So UK mains operates at __________Hz.
In direct current the electrons flow in one direction only. The current supplied by __________ and __________ is d.c.

We can use a Cathode Ray Oscilloscope (CRO) to 'see' electricity. We have already seen this when studying sound. Using a __________ to transform sound waves into an electrical signal, we are able to see patterns in the waveform. A CRO is more commonly used in electronics to study the fast changing signals of a circuit.

CROs are calibrated to allow us to measure aspects of the signal. The CRO draws a voltage-time graph on its screen. Time is on the __________ axis and voltage on the __________. We can vary the scales, allowing us to measure both large and small voltages (or times).

The screen is split into divisions, which we can set to correspond to different values. For example, if a battery is connected and the trace jumps 5 divisions, when we have set the CRO to 3 volts per division, the battery is outputting __________V.

UK mains supply is about 230 volts.

These a.c. traces are at the same __________ but different peak __________.

To work out the frequency from the trace:

Count the number of __________ waves
Use the scale on the CRO to measure the amount of __________
__________ the total time by the number of waves, to find the period
The frequency is the __________ of the period:

Frequency = 1 / Period and Period = 1 / Frequency

On the traces above, if one division equals 0.25 seconds the period of the waves is __________ and therefore the frequency of the wave is __________.

This d.c. trace shows that the __________ does not vary with time.