Supercharge your learning!

Use adaptive quiz-based learning to study this topic faster and more effectively.

Cathode ray oscilloscope (C.R.O.)

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

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.
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 $$2 \times 6 = 12 \text{ V/cm}.$$