Physics 5054/42 — October/November 2011

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

questions

marks

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

Q1Experimental ContextsUse of Techniques, Apparatus and MaterialsAnalysis, Conclusions and EvaluationFree sample

A student measures the focal length of a converging lens.

The student sets up the apparatus as shown in Fig. 1.1.

Fig. 1.1

(a)

The distance $D$ between the illuminated object and the screen is fixed initially at $1.00\text{ m}$ .

(i)

The image on the screen is blurred. Describe the adjustment that the student makes to obtain a sharply focused image, without changing $D$ .

______

(ii)

The focused image is at the top of the screen. Describe one adjustment that the student makes to move the focused image to the centre of the screen.

______

(iii)

The lens is in a holder on a stand. The position of the centre of the lens is to be marked accurately on the stand. Describe how the student does this.

______

(b)

The student finds that, for the same value of $D$ , there are two positions of the lens that produce a focused image on the screen. These positions are at distances $u_1$ and $u_2$ from the illuminated object, as shown in Fig. 1.2.

Fig. 1.2

The two distances $u_1$ and $u_2$ are measured for $D = 1.00\text{ m}$ .
The values obtained are $u_1 = 0.42\text{ m}$ and $u_2 = 0.56\text{ m}$ .

(i)

Calculate the distance $d$ between the two lens positions.

$d$ = ______

(ii)

Theory shows that the focal length $f$ of the lens is given by the relationship

f = \frac{(D^2 - d^2)}{4D}

Calculate $f$ .

$f$ = ______

(c)

The student repeats the experiment for different values of $D$ and calculates values of $(D^2 - d^2)$ each time.

Fig. 1.3 shows the student's results.

Fig. 1.3

$D / \text{m}$	$(D^2 - d^2) / \text{m}^2$
1.10	1.08
1.20	1.18
1.30	1.29
1.40	1.38
1.50	1.47

(i)

On Fig. 1.4, plot the graph of $(D^2 - d^2) / \text{m}^2$ on the y-axis against $D / \text{m}$ on the x-axis.
Start your graph from $(D^2 - d^2) = 0.90\text{ m}^2$ and $D = 1.00\text{ m}$ .
Draw the straight line of best fit.

Fig. 1.4

(ii)

Determine the gradient of the line of best fit. Show your working clearly.

gradient = ______

(iii)

Calculate $f$ using the relationship

f = \frac{\text{gradient}}{4}

$f$ = ______

(d)

Explain why it is better to determine $f$ using the method in (c) rather than the method in (b).

______

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3 more questions

Q2Use of Techniques, Apparatus and Materials · Experimental Contexts6M
Q3Experimental Contexts6M
Q4Use of Techniques, Apparatus and Materials · Analysis, Conclusions and Evaluation · Experimental Contexts5M

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