Physics 9702/31 — October/November 2010

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 resistance of an unknown resistor.

You have been supplied with a chain of eight resistors, as shown in Fig. 1.1.

Fig. 1.1

Connection to one or more of the resistors can be made by attaching a crocodile clip between individual resistors.

The resistance of each individual resistor is $1000\ \Omega$ .
The formula for the total resistance $R$ of resistors in series is

R = R_1 + R_2 + R_3 + ....

(a)

(i)

Set up the circuit in Fig. 1.2, with resistor X in the position shown.

Fig. 1.2

Only the first resistor in the chain is included in the circuit. This has resistance $R$ of $1000\ \Omega$ .

(ii)

Place Z on the resistance wire and move Z until the meter reading is zero.

Measure and record lengths $a$ and $b$ .

$a$ = ______
$b$ = ______

(b)

Vary $R$ by adjusting the position of Y on the chain of resistors.

Repeat (a)(ii) until you have six sets of readings of $R$ , $a$ and $b$ .

Include values of $\frac{b}{a}$ in your table of results.

(c)

(i)

Plot a graph of $\frac{b}{a}$ on the $y$ -axis against $R$ on the $x$ -axis.

(ii)

Draw the straight line of best fit.

(iii)

Determine the gradient of this line.

gradient = ______

(d)

The quantities $a$ , $b$ and $R$ are related by the equation

\frac{a}{b} = \frac{X}{R}

where $X$ is the resistance of resistor X.

Use your answer in (c)(iii) to determine the value of $X$ .
Give an appropriate unit.

$X$ = ______

(e)

Using your graph, determine the value of $R$ that would be needed for the lengths $a$ and $b$ to be equal to each other.

$R$ = ______

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