TEST OF PRACTICAL KNOWLEDGE QUESTION Measure and record the emf, V\(_{o}\) of the cell provided. Connect a circuit as shown in the diagram above. With the k...

(a) Readings and calculations

The e.m.f. of the cell is:

\[V_0=3.0\ \text{V}\]

For example, when \(I=0.20\ \text{A}\) and \(V=0.19\ \text{V}\):

\[I^{-1}=\frac{1}{0.20}=5.00\ \text{A}^{-1},\qquad V^{-1}=\frac{1}{0.19}=5.26\ \text{V}^{-1}.\]

Graph of \(V^{-1}\) against \(I^{-1}\)

Using two widely separated points on the line of best fit, \((2.50,2.63)\) and \((5.00,5.26)\):

\[s=\frac{\Delta V^{-1}}{\Delta I^{-1}}=\frac{5.26-2.63}{5.00-2.50}=\frac{2.63}{2.50}=1.052\ \text{A V}^{-1}.\]

\[s^{-1}=\frac{1}{1.052}=0.950\ \Omega.\]

Precautions

1. All terminals and connecting wires were kept clean and tightly connected.
2. The ammeter and voltmeter were read at eye level to avoid parallax error.

(b)(i) Ohmic conductor

An ohmic conductor is a conductor in which the current is directly proportional to the potential difference across it, provided that the temperature and other physical conditions remain constant.

(b)(ii) Resistivity

Resistivity is the resistance of a material of unit length and unit cross-sectional area. It is given by

\[\rho=\frac{RA}{L}\]

and its SI unit is ohm metre, \(\Omega\,\text{m}\).