Physics 9702/36 — October/November 2012

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

questions

marks

120

minutes

Topics Manipulation, Measurement and Observation · Analysis, Conclusions and Evaluation · Presentation of Data and Observations

Q1Manipulation, Measurement and ObservationAnalysis, Conclusions and EvaluationPresentation of Data and ObservationsFree sample

In this experiment, you will investigate how the light intensity incident on a light sensor varies with distance from the light source.

(a)

You are provided with a lamp mounted inside one end of a black paper tube, together with a light sensor in the form of a light-dependent resistor (LDR) mounted on a half-metre rule, as shown in Fig. 1.1.

Fig. 1.1

(b)

(i)

Measure and record the distance $l$ from the lamp to the open end of the tube, as shown in Fig. 1.1.

$l$ = ______

(ii)

Measure and record the distance $x$ from the front of the LDR to the end of the half-metre rule, as shown in Fig. 1.1.

$x$ = ______

(c)

(i)

Push the rule into the tube until the LDR is approximately half way along the tube, as shown in Fig. 1.2.

Fig. 1.2

(ii)

Record the length $p$ of the half-metre rule inside the tube.

$p$ = ______

(iii)

Calculate the distance $d$ of the LDR from the lamp using $d = l - (x + p)$ .

$d$ = ______

(iv)

Switch on the lamp and record the resistance reading $R$ on the resistance meter.

$R$ = ______ $\text{k}\Omega$

(d)

Repeat (c) using different values of $p$ until you have six sets of values of $p$ and $R$ for $p \leq 20\ \text{cm}$ .
In your table of results include values for $d$ and $d^{1.5}$ ( $d^{1.5} = \sqrt{d^3}$ ).

10M

(e)

(i)

Plot a graph of $R$ on the $y$ -axis against $d^{1.5}$ on the $x$ -axis.

(ii)

Draw the straight line of best fit.

(iii)

Determine the gradient and $y$ -intercept of this line.

gradient = ______
$y$ -intercept = ______

(f)

The quantities $R$ and $d$ are related by the equation

R = ad^{1.5} + b

where $a$ and $b$ are constants.

Using your answers from (e)(iii), determine the values of $a$ and $b$ .
Give appropriate units.

$a$ = ______
$b$ = ______

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Q2Manipulation, Measurement and Observation · Analysis, Conclusions and Evaluation · Presentation of Data and Observations20M

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