A student measures the resistance $R$ of a lamp for different values of the potential difference $V$ across it. The student connects the circuit shown in Fig. 1.1. The student: - closes the switch - connects the crocodile clip at a length $l = 10.0\ \text{cm}$ of the resistance wire - records the potential difference $V$ across the lamp - records the current $I$ in the lamp - opens the switch. Fig. 1.2 shows the readings on the voltmeter and the ammeter. (a) Record in Table…

Physics 5054/42 — October/November 2022

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

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

Q113MObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationUse of Techniques, Apparatus and MaterialsFree sample

A student measures the resistance $R$ of a lamp for different values of the potential difference $V$ across it.

The student connects the circuit shown in Fig. 1.1.

Fig. 1.1

The student:

closes the switch
connects the crocodile clip at a length $l = 10.0\ \text{cm}$ of the resistance wire
records the potential difference $V$ across the lamp
records the current $I$ in the lamp
opens the switch.

Fig. 1.2 shows the readings on the voltmeter and the ammeter.

Fig. 1.2

(a)

Record in Table 1.1 the values of $V$ and $I$ .

Table 1.1

length $l / \text{cm}$	potential difference $V / \text{V}$	current $I / \text{A}$	resistance $R / \Omega$
10.0
30.0	0.7	0.13	5.4
50.0	1.2	0.14	8.6
70.0	1.7	0.16	10.6
90.0	2.2	0.19	11.6
100.0	2.5		11.9

(b)

The student repeats the procedure with different lengths $l$ of the resistance wire.

The student's results are shown in Table 1.1.

(i)

Complete the top row of Table 1.1 by calculating the resistance $R$ of the lamp when $l = 10.0\ \text{cm}$ .

Use the equation shown.

R = \frac{V}{I}

(ii)

The student forgets to write in the current value for $l = 100.0\ \text{cm}$ .

Calculate the current and write its value in Table 1.1.

(c)

The student examines Table 1.1 and states that the resistance $R$ of the lamp is directly proportional to the length $l$ .

State if you agree with the student's statement.

Justify your answer by using values from Table 1.1.

statement ______
justification ______

(d)

(i)

On the grid provided in Fig. 1.3, plot a graph of $R$ on the $y$ -axis against $V$ on the $x$ -axis.

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

Fig. 1.3

Draw a smooth curve of best fit.

(ii)

Using your graph, describe how the resistance $R$ of the lamp changes as the potential difference $V$ across it changes.

(e)

Another student makes changes to the circuit shown in Fig. 1.1.

She uses a variable resistor to vary the current and potential difference, instead of the resistance wire and the crocodile clip.

Complete the circuit diagram in Fig. 1.4 to show how this is done.

Fig. 1.4

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