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In this experiment, you will investigate the variation of a potential difference in a resistor network.
(a) Set up the circuit of Fig. 1.1. The resistor $R$ should have a resistance $R$ where $R = 2.2 \text{k}\Omega$.
(b) Close the switch and record the voltmeter reading $V$, which should be in the range $+0.10V$ to $+0.90V$.
Open the switch. [1]
(c) (i) Change resistor $R$ for one of another value. Close the switch and record the new resistance $R$ and the voltmeter reading $V$.
Open the switch.
(ii) Repeat (c)(i) until you have six sets of readings for $R$ (in k$\Omega$) and $V$. Include in your table of results values for $\left(\frac{R}{R + 1}\right)$, where $R$ is in k$\Omega$.
Some resistors may give negative values for $V$. [11]
(d) (i) Plot a graph of $V$ on the $y\text{-axis}$ against $\left(\frac{R}{R + 1}\right)$ on the $x\text{-axis}$. [3]
(ii) Draw the straight line of best fit. [1]
(iii) Determine the gradient and $y\text{-intercept}$ of this line. [2]
(e) The relationship between $V$ and $R$ is
$V = a\left(\frac{R}{R + 1}\right) - b$
where $a$ and $b$ are constants, and $R$ is in k$\Omega$.
Using your answers from (d)(iii), determine the values of $a$ and $b$.
Give an appropriate unit for $b$. [2]
554
562
591
In this experiment you will investigate the effect of cross-sectional area on the breaking force of polythene.
(a) You are provided with eight strips of polythene, each with a hole at one end. Four of the strips are marked P and four are marked Q. For one of the strips, measure and record the thickness $t$ of the polythene (measure near the end without the hole). [1]
(b) Each strip has two cuts in it, as shown in Fig. 2.1.
For the strips marked P,
(i) measure the distance $w$ between the cuts, [2]
(ii) estimate the percentage uncertainty in $w$. [1]
(c) The cross-sectional area $A$ of the strip between the cuts is shown in Fig. 2.2.
Calculate $A$ using the relationship $A = wt$. [1]
(d) (i) Lay a strip marked P on the bench and hook the newton-meter through the hole. Use a piece of adhesive tape to fix the other end of the strip to the bench, as shown in Fig. 2.3.
(ii) Slowly pull the newton-meter until the strip breaks.
(iii) Repeat (d)(i) and (d)(ii) for the other strips marked P. Record the average breaking force $F$. [2]
(e) Repeat (b)(i), (c) and (d), but this time using the strips marked Q. [3]
(f) (i) It is suggested that the relationship between $F$ and $A$ is
$$ F = kA $$
where $k$ is a constant. 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]
599
540
517
