IB Physics HL B 5 15 Variable Resistance Questions

Practise IB Physics HL B.5.15 by analysing thermistor control circuits, potential dividers and light-dependent resistor responses quantitatively.

Exam points

Analyse how a thermistor changes the potential at a comparator input as temperature changes, using the divider relationship.
Explain how a variable-resistance sensor and control component set a switching threshold for an output such as a heater.

Learn this topic

Study B.5.15—Variable resistance conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 3]

This question is about an operational amplifier (op-amp).

An op-amp is used as a comparator in a circuit, as shown.

Figure for Question IB Physics HL B 5 15 Variable Resistance Questions question 1 — IB Physics HL

The circuit is used to monitor the temperature in a greenhouse. The resistance of a thermistor decreases as its temperature increases.

(a)

Explain how the potential at the inverting input changes as the temperature decreases.

[ 2 ]

(b)

Describe the purpose of component X in the circuit.
When the potential of the non-inverting input is set at 0 V , the heater switches on at a temperature of around $10^{\circ} \mathrm{C}$ . The ideal temperature to grow plants in the greenhouse is $18^{\circ} \mathrm{C}$ or greater. At $18^{\circ} \mathrm{C}$ the resistance of the thermistor is $193 \Omega$ .

[ 1 ]

All question bank results loaded

Learn this topic

IB Physics HL B 5 15 Variable Resistance Questions question 1

Question (a)

Question (b)