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# Cathode ray oscilloscope (C.R.O.)

## C.R.O. description

A cathode-ray oscilloscope (C.R.O.) is an instrument that displays the waveforms of different types of electrical signals.

The waveform of a signal is its voltage plotted against time.

The $x$-axis on the display corresponds to time and the $y$-axis corresponds to voltage.

Signals generated by electric currents, human heartbeats and sound waves picked up by a microphone can all be displayed on a C.R.O.

An oscilloscope is connected to an electrical circuit in parallel just like a voltmeter.

Left: Cathode ray oscilloscope (C.R.O.) apparatus. Right: Signals on an oscilloscope screen.

## C.R.O. display

The screen of a cathode-ray oscilloscope (C.R.O.) is divided into ($1\text{ cm}$ by $1\text{ cm}$) squares.

The vertical gain control adjusts the voltage in volts per square on the vertical axis (e.g. $1\text{ V/cm}$, $2\text{ V/cm}$).

Halving the vertical gain control setting doubles the height of the displayed waveform.

The time-base control adjusts the time in seconds per square on the horizontal axis (e.g. $1\text{ ms/cm}$, $2\text{ ms/cm}$).

Halving the time-base control setting causes the displayed waveform to become twice as wide.

A waveform as displayed on a C.R.O.

The period of the wave is four squares (along the horizontal axis). If the time-base setting is set to $5 \text{ ms/cm}$ then the period is $4 \times 5 = 20 \text{ ms/cm}.$

The amplitude of the wave is two squares (along the vertical axis). If the vertical gain is set to $6 \text{ V/cm}$ then the amplitude is then $2 \times 6 = 12 \text{ V/cm}.$