A student investigates how the potential difference (p.d.) $V$ across a fixed resistor R changes as extra resistance is added to the circuit. (a) - She sets up the circuit shown in Fig. 1.1. - She connects the crocodile clip C to a point on the resistance wire at a length $l = 20.0\text{ cm}$ from end X. - She closes the switch. - She reads the voltmeter and records the reading. - She opens the switch. Fig. 1.2 shows the voltmeter reading. (i) Read the voltmeter scale and in…

Physics 5054/42 — May/June 2021

Cambridge O-Level · Alternative to Practical · worked solutions for every part, with the mark scheme

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Topics Experimental Contexts · Analysis, Conclusions and Evaluation · Use of Techniques, Apparatus and Materials · Observations and Measurements

Q114MObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationUse of Techniques, Apparatus and MaterialsFree sample

A student investigates how the potential difference (p.d.) $V$ across a fixed resistor R changes as extra resistance is added to the circuit.

(a)

She sets up the circuit shown in Fig. 1.1.

Fig. 1.1

She connects the crocodile clip C to a point on the resistance wire at a length $l = 20.0\text{ cm}$ from end X.
She closes the switch.
She reads the voltmeter and records the reading.
She opens the switch.

Fig. 1.2 shows the voltmeter reading.

Fig. 1.2

(i)

Read the voltmeter scale and in Table 1.1 on page 4, record the p.d. $V$ .

(ii)

Calculate $\frac{1}{V}$ and record its value in Table 1.1 on page 4 to the appropriate number of significant figures.

(b)

She repeats the procedure in (a) using values of $l = 30.0\text{ cm}$ , $40.0\text{ cm}$ , $60.0\text{ cm}$ and $80.0\text{ cm}$ . Her results are shown in Table 1.1.

Table 1.1

length $l$ / $\text{cm}$	potential difference $V$ / $\text{V}$	$\frac{1}{V}$ / $\frac{1}{\text{V}}$
20.0
30.0	1.3	0.77
40.0	1.1	0.91
60.0	0.90	1.1
80.0	0.80	1.3

Suggest why the student opens the switch between readings.

(c)

On the grid provided in Fig. 1.3 on page 5, plot a graph of $\frac{1}{V}$ on the y-axis against $l$ on the x-axis.

Start both axes from the origin (0, 0).

Draw the best-fit straight line.

Fig. 1.3

(d)

(i)

Calculate the gradient $m$ of your line. Show all working and indicate on the graph the values you use.

$m$ = ______

(ii)

Extend your line until it crosses the y-axis.

Measure the intercept $c$ that your line makes with the y-axis.

$c$ = ______

(e)

Calculate the electromotive force (e.m.f.) $E$ of the cell using the equation:

E = \frac{k}{c}

where $k = 1.0\text{ V}$ .

$E$ = ______ $\text{V}$

(f)

Suggest one practical reason why, despite carrying out the experiment with care, the student's value for $E$ may not be the true value.

(g)

The results in Table 1.1 show that as the length $l$ of resistance wire increases, the potential difference $V$ decreases.

State how the results show that $l$ is not inversely proportional to $V$ .

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3 more questions

Q2Use of Techniques, Apparatus and Materials · Analysis, Conclusions and Evaluation8M
Q3Experimental Contexts4M
Q4Experimental Contexts · Analysis, Conclusions and Evaluation4M

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