AS & A Level Physics - 9702 Paper 3 2015 Summer Zone 1

In this experiment, you will investigate how the current in a circuit varies as the resistance of the circuit is changed.
(a) (i) You have been provided with a length of bare wire and two crocodile clips which have small screws on them. Connect the wire between the crocodile clips using the screws as shown in Fig. 1.1.

The length $w$ of wire between the screws should be approximately 50cm. The screws should be tightened using the screwdriver.

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(ii) Measure and record $w$.

$w$ = ............................................................ [1]
(b) (i) Set up the circuit as shown in Fig. 1.2.

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(ii) Close the switch.
(iii) Record the ammeter reading $I_A$.

$I_A$ = ..........................................................
(iv) Open the switch.
(c) (i) Move the crocodile clip to set up the circuit as shown in Fig. 1.3.

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(ii) Close the switch.
(iii) Record the ammeter reading $I_B$.

$I_B$ = .......................................................... [1]
(iv) Open the switch.
(d) Change $w$ and repeat (a)(ii), (b) and (c) until you have six sets of values of $w$, $I_A$ and $I_B$. Include values of $\left( \frac{I_A + I_B}{I_A / I_B} \right)$ in your table. [10]
(e) (i) Plot a graph of $\left( \frac{I_A + I_B}{I_A / I_B} \right)$ on the $y$-axis against $w$ on the $x$-axis. [3]
(ii) Draw the straight line of best fit. [1]
(iii) Determine the gradient and $y$-intercept of this line.

gradient = ..........................................................

$y$-intercept = ....................................................... [2]
(f) The quantities $I_A$, $I_B$ and $w$ are related by the equation $\left( \frac{I_A + I_B}{I_A / I_B} \right) = Mw + N$ where $M$ and $N$ are constants.

Using your answers in (e)(iii), determine values for $M$ and $N$. Give appropriate units.

$M$ = ...............................................................
$N$ = ............................................................... [2]

(a) (i) Measure and record the length $L$ of the longer wooden strip as shown in Fig. 2.1.

Fig. 2.1
$L = \text{.............................................}$ [1]
(ii) Measure and record the mass $m$, in grams, of the longer wooden strip.
$$m = \text{............................................. g}$$ [1]
(iii) Calculate the mass per unit length $p$ of the wood, where
$$p = \frac{m}{L}.$$
$$p = \text{.............................................}$$
(iv) Justify the number of significant figures that you have given for your value of $p$.
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[1]

(b) (i) Measure and record the mass $M$, in grams, of the slotted mass.
$$M = \text{............................................. g}$$ [1]
(ii) Use the Blu-Tack to attach the slotted mass to the top of the longer wooden strip as shown in Fig. 2.2.

Fig. 2.2
The centre of the slotted mass should be positioned at the end of the wooden strip.
(iii) Calculate $C$, where
$$C = \frac{L^2}{2(M + Lp)}.$$
$$C = \text{.............................................}$$ [1]

(c) (i) Balance the wooden strip on the pivot as shown in Fig. 2.3.

Fig. 2.3
(ii) Measure and record the distance $x$ from the pivot to the end of the wooden strip as shown in Fig. 2.3. Do not mark the wooden strip.
$$x = \text{.............................................}$$ [1]
(iii) Estimate the percentage uncertainty in your value of $x$.
percentage uncertainty = ............................................. [1]

(d) Repeat (a)(i), (b)(ii), (b)(iii), (c)(i) and (c)(ii) for the shorter wooden strip.
$$L = \text{.............................................}$$
$$C = \text{.............................................}$$
$$x = \text{.............................................}$$ [3]

(e) It is suggested that the relationship between $x$ and $C$ is
$$x = kC$$
where $k$ is a constant.
(i) Using your data, calculate two values of $k$.
first value of $k = ext{.............................................}$
second value of $k = ext{.............................................}$ [1]
(ii) Explain whether your results in (e)(i) support the suggested relationship.
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[1]

(f) (i) Describe four sources of uncertainty or limitations of the procedure for this experiment.
1. .....................................................................................
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2. .....................................................................................
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3. .....................................................................................
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4. .....................................................................................
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[4]
(ii) Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures.
1. .....................................................................................
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2. .....................................................................................
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3. .....................................................................................
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4. .....................................................................................
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[4]