Edexcel A-Level Physics Resistance and Ohm’s Law

Practise Edexcel A-Level Physics resistance and Ohm’s law using I-V data, circuit diagrams, resistor purpose and negligible resistance judgements.

Exam points

check graph current values against V = IR and stated circuit resistance data
draw ammeter-voltmeter circuits with the voltmeter parallel to the component tested
judge when wire resistance is negligible compared with the measured component resistance

[Maximum number: 3]

A student set up the circuit shown to investigate the properties of a negative temperature coefficient thermistor.

Figure for Question 2.4.66 - Resistance and Ohm’s law question 1 — Edexcel A-Level Physics AS

The power supply has negligible internal resistance.

Show that the voltmeter reading was about 6 V .
ammeter reading $=23 \mathrm{~mA}$

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$\text { Use of } \frac{1}{R}=\frac{1}{500 \Omega}+\frac{1}{600 \Omega}$

Use of V=I R

Voltmeter reading $=6.3(\mathrm{~V})$

Example of calculation
$\begin{aligned} & \frac{1}{R_{\text {parallel }}}=\frac{1}{500 \Omega}+\frac{1}{600 \Omega}, \text { so } R_{\text {parallel }}=273 \Omega & V=I R=23.0 \times 10^{-3} \mathrm{~A} \times 273 \Omega=6.28 \mathrm{~V} \end{aligned}$

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2.4.66 - Resistance and Ohm’s law question 1