Physics 5054/41 — May/June 2019

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

questions

marks

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

Q113MExperimental ContextsObservations and MeasurementsAnalysis, Conclusions and EvaluationUse of Techniques, Apparatus and MaterialsFree sample

A student investigates how the resistance of a light-dependent resistor (LDR) depends on the brightness of light.

He uses a lamp to vary the brightness of light on the LDR. The LDR is mounted on a wooden block so that it is a distance $l$ above the bench. The lamp is placed directly above the LDR at a distance $h$ above the bench, as shown in Fig. 1.1.

Fig. 1.1

(a)

(i)

On Fig. 1.1, measure the distances $l$ and $h$ .

$l$ = ______ $\text{cm}$
$h$ = ______ $\text{cm}$

(ii)

Calculate the distance $d$ from the lamp to the LDR.

$d$ = ______ $\text{cm}$

(iii)

The student uses a ruler to measure $h$ .

Suggest one difficulty that the student has when making this measurement.

(b)

(i)

Fig. 1.2 shows some of the apparatus used in the experiment.

Fig. 1.2

In the space below, draw a circuit diagram for this apparatus.

(ii)

Fig. 1.3 shows the readings of voltage $V$ across the LDR and current $I$ in the circuit when the lamp is at the distance $d$ above the LDR calculated in (a)(ii).

Fig. 1.3

(1)

Record the readings $V$ and $I$ .

$V$ = ______ $\text{V}$
$I$ = ______ $\text{mA}$

(2)

The resistance $R$ of the LDR for this lamp position is calculated using the equation:

R = \frac{V}{I}

Calculate $R$ , giving your answer to 2 significant figures with unit.

$R$ = ______

(c)

The student repeats the experiment for different values of $d$ . The results are shown in Table 1.1.

Table 1.1

$d / \text{cm}$	$I / \text{mA}$

7.0	43
11.1	28
19.0	16
26.8	12
35.0	10

(i)

Use the readings taken in (a)(ii) and (b)(ii) to complete the top row of Table 1.1.

On the grid in Fig. 1.4, plot the graph of $I / \text{mA}$ on the $y$ -axis against $d / \text{cm}$ on the $x$ -axis. Start your axes from (0,0).

Draw the smooth curve of best fit.

Fig. 1.4

(ii)

The voltage $V$ is constant throughout. Suggest how the resistance $R$ of the LDR varies with $d$ .

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