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In this experiment, you will investigate the length of a loaded spring as the load is varied.
(a) Measure and record the length $L$ of the metal rod.
(b) (i) Support the rod as shown in Fig. 1.1.
(ii) Adjust the position of the pivot so that it is approximately 5 cm from the free end of the rod.
(iii) Adjust the clamp so that the rod is horizontal and the spring is vertical.
(c) Measure and record the length $h$ of the coiled part of the spring and the distance $d$ from the pivot to the point where the spring is attached to the rod.
(d) Repeat (b)(iii) and (c) for different positions of the pivot along the rod until you have six sets of readings of $d$ and $h$. Include values of $1/d$ in your table of results.
(e) (i) Plot a graph of $h$ on the $y$-axis against $\frac{1}{d}$ on the $x$-axis.
(ii) Draw the line of best fit.
(iii) Determine the gradient and $y$-intercept of this line.
(f) It is suggested that the relationship between $d$ and $h$ is
$$h = \frac{A}{d} + B$$
where $A$ and $B$ are constants.
The value of $A$ is equal to $\frac{Wz}{k}$
where $W$ is the weight of the rod,
$k$ is the spring constant of the spring
and $z$ is a constant.
The values for $W$ and $k$ are given on the card.
Use your answer from (e)(iii) and the values on the card to calculate $z$.
Give the appropriate unit.
562
569
564
In this experiment, you will investigate the effect of an electric current on a nearby magnet.
(a) A circuit has been set up for you as shown in Fig. 2.1. Do not adjust the position of the stands.
Switch on the current. Use the variable resistor to adjust the current $I$ to about 2A. Record your value of current.
(b) Switch off the current. Place the thread over the horizontal copper wire, so that the magnet hangs as shown in Fig. 2.2.
(c) By moving your hand, adjust the distance $x$ between the copper wire and the dotted line along the side of the magnet to about 7 cm. Record your value of $x$
(d) Place the protractor on the bench beneath the magnet. Switch on the current. The magnet will turn through an angle. Wait until the magnet comes to rest. Measure and record the angle $\theta$ turned through by the magnet. Switch off the current.
(e) Estimate the percentage uncertainty in your value of $\theta$.
(f) (i) Reverse the direction of the current in the copper wire. Repeat (d) to find a second value of $\theta$.
(ii) Use your answers to (d) and (f)(i) to determine an average value of the magnitude of $\theta$.
(g) Change $x$ to about 4 cm. Adjust the value of $I$ so that the deflection $\theta$ is the same as in (f)(ii). Record $x$ and $I$.
(h) It is suggested that, for a given value of $\theta$, the relationship between $I$ and $x$ is $I = kx$ where $k$ is a constant.
(i) Using your data, calculate two values of $k$.
(ii) Explain whether your results support the suggested relationship.
(iii) Justify the number of significant figures that you have given for your values of $k$.
(i) (i) Describe four sources of uncertainty or limitations of the procedure in this experiment.
(ii) Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures.
569
579
542
