The diagram illustrates an electrical circuit used to investigate a science experiment. The rheostat is adjusted to vary the current and voltage in the circuit. Fig 2 (a) and Fig 2 (b) below illustrate ammeter readings I=I1, I2, I3, I4, I5 and voltmeter readings v=v1, v2, v3, v4, and v5, in table 1 below respectively when the key is closed.

2(a).

The meter scales show the following values for the needle positions:

$$\begin{array}{|c|c|c|} \hline I_\mathrm{L} & I_\mathrm{M} & I_\mathrm{R} \\ \hline 0.20~\mathrm{A} & 0.40~\mathrm{A} & 0.60~\mathrm{A} \\ \hline \end{array}$$

2(b).

The meter scales show the following values for the needle positions (in volts):

$$\begin{array}{|c|c|c|} \hline V_\mathrm{L} & V_\mathrm{M} & V_\mathrm{R} \\ \hline 1.0~\mathrm{V} & 2.0~\mathrm{V} & 3.0~\mathrm{V} \\ \hline \end{array}$$

For low setting:
$R = \frac{V_\mathrm{L}}{I_\mathrm{L}} = \frac{1.0}{0.20} = 5.0~\Omega$

For medium setting:
$R = \frac{V_\mathrm{M}}{I_\mathrm{M}} = \frac{2.0}{0.40} = 5.0~\Omega$

For high setting:
$R = \frac{V_\mathrm{R}}{I_\mathrm{R}} = \frac{3.0}{0.60} = 5.0~\Omega$

Average resistance $R = 5.0~\Omega$.

Plot the points: $(1.0, 0.20)$, $(2.0, 0.40)$, $(3.0, 0.60)$.

The graph is a straight line through origin with slope $\frac{1}{R} = 0.20~\mathrm{A/V}$.

R = 5.0 \Omega