IB Physics SL B.5.13 Series and Parallel Circuits

Practise reducing resistor networks and using shared current or potential difference to calculate branch values, power changes and the effect of switches or variable components.

Exam points

add series resistances and use reciprocal addition for parallel branches before simplifying the network
use equal series current and equal parallel potential difference to determine branch quantities
predict how opening, closing or adjusting a branch changes total resistance, current and component power

[Maximum number: 4]

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.5.13—Series and parallel circuits question 1 — IB Physics SL

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

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

Determine the temperature of X when the potential difference across R is 4.5 V .

$V_X = 7.5\ ext{V}$ .
$I = \frac{4.5}{100 imes 10^3} = 4.5 imes 10^{-5}\ ext{A}$ OR $\frac{V_X}{V_R}=\frac{R_X}{R_R}$ .
$R_X = \frac{7.5}{4.5 imes 10^{-5}} = 1.67 imes 10^5\ \Omega$ OR $R_X=\frac{7.5}{4.5} imes100 imes10^3=1.67 imes10^5\ \Omega$ .
T=-37 or $-38\ ^\circ ext{C}$ .

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B.5.13—Series and parallel circuits question 1