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In this experiment, you will investigate the change in current in a circuit as its resistance is changed.
(a) (i) Assemble the circuit of Fig. 1.1.
(ii) Close the switch.
(iii) Record the ammeter reading $I_0$. [1]
(iv) Open the switch.
(b) (i) Select one of the resistors labelled with a numerical value and connect it between the crocodile clips on the component holder. Record the resistance $R$ of your selected resistor.
(ii) Close the switch and record the ammeter reading $I$. Open the switch. [1]
(c) Repeat (b) using different labelled resistors until you have six sets of values of $R$ and $I$. Include values of $\frac{1}{R}$ in your table. [10]
(d) (i) Plot a graph of $I$ on the $y$-axis against $\frac{1}{R}$ on the $x$-axis. [3]
(ii) Draw the straight line of best fit. [1]
(iii) Determine the gradient and $y$-intercept of this line. [2]
(e) The quantities $I$ and $R$ are related by the equation $I = \frac{a}{R} + \frac{a}{b}$
where $a$ and $b$ are constants.
Using your answers from (d)(iii), determine the values of $a$ and $b$. Give appropriate units. [2]
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581
In this experiment, you will investigate the time taken for a ball to roll a fixed distance down an inclined track.
(a) You are provided with a pendulum which can be used to hit and bend a wire specimen. Attach the wooden pointer to the pendulum using Blu-Tack. Align the pointer with the 90° position on the protractor when the pendulum is hanging freely, as shown in Fig. 2.1. Check that the pendulum swings freely.
(b) You are provided with copper wire specimens of two different diameters. Using the micrometer, measure and record the diameter $d$ of one of the thicker wires. [2]
(c) Estimate the percentage uncertainty in your value of $d$. [1]
(d) (i) Fit the wire fully into the hole in the wooden block. The wire should project about 2 cm above the surface of the block.
(ii) Position the wooden block so that the wire just touches the edge of the pendulum, as shown in Fig. 2.2.
(iii) Lift the pendulum so that the pointer is aligned with the 0° position on the protractor.
(iv) While holding the block in position, release the pendulum and record the maximum angle $\theta$ reached by the pointer after the pendulum has bent the wire. [2]
(v) The energy used to bend the wire is proportional to the value of $\sin(180°-\theta)$. Calculate this value, giving your answer to an appropriate number of significant figures. [2]
(e) Repeat (b) and (d) using the thinner wire specimens. [3]
(f) It is suggested that the relationship between $\theta$ and $d$ is $\sin(180°-\theta) = kd^2$ where $k$ is a constant.
(i) Using your data, calculate two values of $k$. [1]
(ii) Explain whether your results support the suggested relationship. [1]
(g) (i) Describe four sources of uncertainty or limitations of the procedure for this experiment. [4]
(ii) Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures. [4]
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