Physics 9702/33 — May/June 2013

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

questions

marks

120

minutes

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

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

In this experiment, you will determine the resistivity of a metal in the form of a wire.

(a)

(i)

Measure and record the diameter $d$ of the short sample of wire that is attached to the card. You may remove the wire from the card.

$d$ = ______

(ii)

Calculate the cross-sectional area $A$ of the wire, in $\text{m}^2$ , using the formula

A = \frac{\pi d^2}{4}

$A$ = ______ $\text{m}^2$

(b)

(i)

Using the wire attached to the metre rule, set up the circuit shown in Fig. 1.1.

Fig. 1.1

There are two crocodile clips labelled P and Q.
P will remain in the same position throughout the experiment.
Q can be moved to different positions along the wire.

(ii)

Position the slider approximately half-way along the rheostat (variable resistor).

(iii)

Attach Q approximately half-way along the wire.

(iv)

Switch on the power supply.

(v)

Measure and record the length $l$ of wire between P and Q.
Record the voltmeter reading $V$ .

$l$ = ______ $\text{m}$
$V$ = ______ $\text{V}$

(vi)

Record the ammeter reading $I$ .
( $1\ \text{mA} = 0.001\ \text{A}$ )

$I$ = ______ $\text{A}$

(vii)

Switch off the power supply.

(c)

(i)

Reposition Q at a new distance $l$ from P.

(ii)

Switch on the power supply.

(iii)

Adjust the slider on the rheostat until the ammeter reading is the same value as in (b)(vi).

(iv)

Measure and record the length $l$ of wire between P and Q.
Record the voltmeter reading $V$ .

$l$ = ______ $\text{m}$
$V$ = ______ $\text{V}$

(v)

Switch off the power supply.

(d)

Repeat (c) until you have six sets of readings of $l$ and $V$ .

For each value of $l$ , adjust the slider on the rheostat so that the ammeter reading $I$ remains constant at the value in (b)(vi).

You may find it helpful to copy your value from (b)(vi) here.

$I$ = ______ $\text{A}$

Include values of $\frac{V}{l}$ and $\frac{1}{l}$ in your table.

10M

(e)

(i)

Plot a graph of $\frac{V}{l}$ on the $y$ -axis against $\frac{1}{l}$ 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 $V$ and $l$ are related by the equation

\frac{V}{l} = \frac{M}{l} - N

where $M$ and $N$ are constants.

(i)

Use your answers in (e)(iii) to determine values for $M$ and $N$ .

$M$ = ______ $\text{V}$
$N$ = ______ $\text{V m}^{-1}$

(ii)

The resistivity $\rho$ of the material of the wire, in $\Omega\ \text{m}$ , can be found using the relationship

\rho = \frac{NA}{I}

Using your answers in (a)(ii), (b)(vi) and (f)(i), calculate a value for $\rho$ .

$\rho$ = ______ $\Omega\ \text{m}$

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