Worked Example: Potential Divider with Thermistor
Electrical Circuits - OCR A-Level Physics
Worked Example
A potential dividerA circuit that uses two or more resistors in series to produce a fraction of the source voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. across one of the resistors. uses a fixed resistor R_1 = 12 k-ohm and an NTC thermistorA component whose resistance decreases significantly as temperature increases (negative temperature coefficient). as R_2. The supply is 6.0 V. At 25 degrees C the thermistorA component whose resistance decreases significantly as temperature increases (negative temperature coefficient). has resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A).. Measured in ohms (Ω). 10 k-ohm. At 100 degrees C it has resistanceThe opposition to currentThe rate of flow of charge. Measured in amperes (A). flow. The ratio of potential difference to current. Measured in ohms (Ω). 1.0 k-ohm. Calculate V_out across the fixed resistor at 100 degrees C.
Show Solution
1
Identify the output
2
Use the potential dividerA circuit that uses two or more resistors in series to produce a fraction of the source voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit charge between two points. Measured in volts (V). Informal term for potential difference. across one of the resistors. equation for R_1
3
Substitute values at 100 degrees C
4
Calculate
Answer
The p.d. across the fixed resistor at 100 degrees C is 5.5 V. As temperature increased, the thermistorA component whose resistance decreases significantly as temperature increases (negative temperature coefficient). resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). fell from 10 k-ohm to 1.0 k-ohm, so most of V_in now drops across R_1.