Electronics

Abstract

Light-dependent resistors (LDRs), light-emitting diodes (LEDs) and thermistors are all examples of transducers (i.e. theyconvert energy or information from one form to another). The resistance of a light-dependent resistor decreases as the intensity of the light falling on it increases. (LDRs are sometimes used in light meters. Selenium cells are also used in light meters. When light falls on the cell, a small p.d. results from the movement of the electrons.) LEDs are semiconductor diodes which convert electrical energy into light energy. To avoid damage by large currents, a protective resistor is usually connected in series with the LED. The diagram opposite shows a circuit with an LDR and an LED in it. When light shines on the LDR, the LED switches off.