What is a photoelectric cell? Describe its construction and working, and give two uses.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define it. A device that converts light into an electric current using the photoelectric effect.
2 · Describe the construction. Evacuated bulb; semi-cylindrical cathode coated with a low work function metal; wire anode of nickel or platinum; battery and microammeter.
3 · Draw it. [Diagram: bulb, curved cathode, wire anode, incident light, battery with the anode positive, microammeter]
4 · Explain the working. Light frees electrons from the cathode; the anode collects them; the saturation current is proportional to the intensity of light.
5 · Give two uses. Reproducing sound from cinema film; burglar alarms.
6 · Close in one line. So, a photocell lets light switch or control a circuit.
Scoring tip: A neat labelled diagram with the light arrows earns at least a mark. Write uses as full phrases, not single words.
