Investigate this If several resistors are connected in series what happens to the overall resistance in the circuit?
Light dependent resistors (LDR) Light dependent resistors vary the amount of current that can pass through them depending on the amount of light shining on them. When there is very little light, the resistance is high and very little current can pass through. When there is a lot of light, then the resistance is low and they conduct electricity well. LDRs are used to detect the amount of light. They are used in processes such as detecting light levels in cameras; turning street lights on in darkness; and adjusting screen brightness automatically. The input is the light level and the output is the amount of current they allow to flow through them.
Fig. 5 The symbol for an LDR. Activity How light affects an LDR
Apparatus LDR, LED, leads, lamp, ohmmeter (found on a multimeter), battery, metre stick Method 1. Set up the circuit as shown. 2. Copy the table of results
100 cm 90 cm 80 cm 70 cm 60 cm 50 cm 40 cm 30 cm 20 cm 10 cm 0 cm
348
3. Connect an ohmmeter (multimeter) to measure resistance across the LDR. 4. Place a lamp pointing at the LDR standing 100 cm away. 5. Record the resistance across the LDR and observe the LED. 6. Bring the lamp 10 cm closer. Record the resistance and observe the LED. 7. Repeat step 6 until the lamp is at the 0 cm mark.
LED
Multimeter
LDR
Distance between lamp and LDR Resistance (ohms) Observation of LED
