Resistance changes in thermistors and LDRsEdexcel International A Level Physics: Mind map

Exam questions on Resistance changes in thermistors and LDRs

1. A technician heats a metal wire and a negative temperature coefficient (NTC) thermistor, one at a time, from 20 °C to 80 °C. Each is connected to a constant 5.0 V supply of negligible internal resistance through an ammeter.
   The thermistor current is 2.0 mA at 20 °C and 12.5 mA at 80 °C. Calculate the resistance of the thermistor at each temperature.2 marks
2. A light-dependent resistor (LDR) is connected to a 6.0 V supply of negligible internal resistance through an ammeter. The ammeter reads 12 mA in bright light and 0.10 mA in darkness.
   Calculate the resistance of the LDR in darkness and how many times larger it is than in bright light.2 marks
3. A thermistor is connected across a 5.0 V supply of negligible internal resistance. Its resistance is 2.0 kΩ at 25 °C and 0.30 kΩ at 75 °C.
   Calculate the current in the thermistor at each temperature and the percentage increase in the current between 25 °C and 75 °C.3 marks