Flickering lights: results

A filament lamp produced the following trace, with a frequency of 100 Hz.

Filament Lamp frequency

A computer monitor gave the following frequency using the meter function:

computer monitor frequency

The graphs below show how V (blue), I (purple) and P (yellow) vary with time.

Voltage, Current, Power

The key point is that the power is always a positive quantity, and varies sinusoidally with a frequency = 2 x frequency of the mains voltage.

Teachers’ notes

Care should be taken not to place the DrDAQ too close to a CRT TV screen as there is a possibility of damage due to a shock caused by the build-up of electrostatic charge on the screen.

The light-dependent resistor used as the sensor in this experiment does not respond rapidly to changes in light level, but it does produce a small change in resistance that can be used to record the change in light intensity.

Credits, comments and further info

Submitted By:

Peter Webber 
Exmouth Community College.
Devon UK

Any comments / suggestions for improvements, please e-mail him at: