Resistance changes in thermistors and LDRsEdexcel International A Level Physics: Flashcards
What these 12 flashcards ask
- Why does the resistance of a metal increase with temperature?
- Does the number of conduction electrons in a metal change much with temperature?
- What is an NTC thermistor?
- Why does the resistance of an NTC thermistor fall when heated?
- In a thermistor, why does extra lattice vibration not raise the resistance?
- What is an LDR?
- Why does the resistance of an LDR fall in bright light?
- What is the resistance of an LDR like in the dark?
- Which equation shows how the number of charge carriers affects current?
- Name one use of a thermistor.
- Name one use of an LDR.
- Does the thermistor change in resistance linearly with temperature?
Exam questions on Resistance changes in thermistors and LDRs
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).