# The Oscilloscope

An oscilloscope can be used to show the sizes of voltages and currents in both d.c. and a.c. circuits. This is what a typical oscilloscope looks like. A trace would be seen on the grid display.

D.C. Traces (Also seen in GCSE Physics 2)

If we connected a battery or cell to an oscilloscope, we would see a trace similar to the one shown here. The current of a d.c. supply is constant, this means the voltage is constant.

We see a straight line.

A.C. Traces (Also seen in GCSE Physics 2)

If we connect anything that draws power from the Mains to an oscilloscope we will see a similar trace to the one shown here. The current is constantly changing from maximum flow in one direction to maximum flow in the other direction; this means the voltage is doing the same.

We see a wave.

# Controls

There are two main controls that we use are the volts/div and time base dials:

The volts/div (volts per division) dial allows you to change how much each vertical square is worth.

The time base dial allows you to change how much each horizontal square is worth.

Voltage

We can measure the voltage of a d.c. supply by counting the number or vertical squares from the origin to the line and then multiplying it by the volts/div. In the trace the line is 2.5 squares above 0, if each square is worth 5 volts the voltage is (2.5 x 5) 12.5 volts.

We can measure the peak voltage of an a.c. supply by counting how many vertical squares from the centre of the wave to the top and then multiplying it by the volts/div (how much voltage each square is worth). In the trace the peak voltage is 4 squares high, if each square is worth 5 volts the voltage is (4 x 5) 20 volts.

Time and Frequency

We can measure the time for one period (wave) by counting how many horizontal squares one wavelength is and then multiplying it by the time base (how much time each square is worth).

In the trace above one wave is 6 squares long, if each square is worth 0.02 seconds the time for one wave is 0.12 seconds.

We can calculate the frequency (how many waves or many times this happens per second) using the equation:

and

If the time period is 0.12 seconds, the frequency is 8.33Hz

Frequency is measured in Hertz, Hz