Resistance of a light emitting diode and distance from light source
An experiment was carried out where a light source was moved further away from a light dependent resistor (LDR) in 5.0 cm steps. The voltage across the LDR and the current through it were measured three times for each distance and then averaged. The average resistance of the LDR was calculated using R = V/I from Ohm's Law. This resistance was plotted against the distance of the light source from the LDR.
It can bee seen from the graph that there is an increase in resistance of the LDR as the light source increases its distance from the LDR. The line of best fir was a curve, showing that the resistance increases more at further distances.
Mandatory Knowledge
Measurement of current, potential difference (voltage) and resistance, using appropriate meters in simple and complex circuits.
Knowledge of the circuit symbol, function and application of standard electrical and electronic components: cell, battery, lamp, switch, resistor, voltmeter, ammeter, LED, motor, microphone, loudspeaker, photovoltaic cell, fuse, diode, capacitor, thermistor, LDR, relay, transistor.
For transistors, knowledge of the symbols for an npn transistor and an n-channel enhancement mode MOSFET. Explanation of their function as a switch in transistor switching circuits.
Application of the rules for current and potential difference (voltage) in series and parallel circuits.
Last updated: 27/04/2023