IB Physics SL B.5.15 Variable Resistance Question Bank

Practise IB Physics SL B.5.15 by reading variable-resistance graphs and predicting current, voltage and sensitivity in thermistor, LDR and potentiometer circuits.

Exam points

Read thermistor data to relate temperature, resistance and the circuit current or voltage.
Use LDR resistance changes to predict ammeter and voltmeter readings in a series circuit.
Interpret a potentiometer slider and identify how its position changes the measured potential.

[Maximum number: 3]

This question is in two parts. Part 1 is about a thermistor circuit. Part 2 is about vibrations and waves.
Part 1 Thermistor circuit
The circuit shows a negative temperature coefficient (NTC) thermistor X and a $100 \mathrm{k} \Omega$ fixed resistor R connected across a battery.

Figure for Question B.5.15—Variable resistance question 1 — IB Physics SL

The battery has an electromotive force (emf) of 12.0 V and negligible internal resistance.

(a)

The graph below shows the variation with temperature T of the resistance $R_{\mathrm{x}}$ of the thermistor.

[ 3 ]

(i)

State the range of temperatures for which the change in the resistance of the thermistor is most sensitive to changes in temperature.

[ 1 ]

50 to (up to) $-30^{\circ} \mathrm{C} /$ at low temperatures;

(ii)

State and explain the effect of a decrease in temperature on the ratio

\frac{\text { voltage across } \mathrm{X}}{\text { voltage across } \mathrm{R}}

Part 2 Vibrations and waves

The cone and dust cap D of a loudspeaker L vibrates with a frequency of 1.25 kHz with simple harmonic motion (SHM).

Figure for Question (ii) — IB Physics SL

[ 2 ]

as the temperature decreases $R_{X}$ increases; same current through R and X so the ratio increases or $V_{X}$ increases and $V_{R}$ decreases so the ratio increases;

Part 2 Vibrations and waves

All question bank results loaded

B.5.15—Variable resistance question 1

Question (a)

Question (i)

Question (ii)