Determination of Resistivity – Viva Questions

Resistivity \(\rho\) is a material-specific property that measures how strongly a material opposes the flow of electric current. Its SI unit is ohm-meter \(\Omega m\).

Ohm’s Law states that the potential difference \(V\) across a conductor is directly proportional to the current \(I\) flowing through it, provided the temperature remains constant. Mathematically, \(V=IR\), where \(R\) is the resistance of the conductor.

Resistivity is material-spcific property only while resistance includes geometrical aspects also. The relation between the two is given by \(R = \rho \frac{L}{A}\) where \(\rho\) is the resistivity, \(L\) is the length of the wire, and \(A\) is its cross-sectional area.

We measure the potential difference by voltmeter. We put it in parallel across the points.

We will place an ammeter in series with the resistor. Its reading tells the current passing through it.

The graph helps determine the resistance of the wire. The slope of the \(V−I\) graph gives the resistance, as \(R = \frac{V}{I}\).

The slope represents the resistance \(R\) of the wire.

The resistivity of a material depends on its atomic structure, and its lattice, its temperature and presence of impurities in it. Materials with valence electros free to move have less resistivity. Higher temperature increases resistivity in metals while decreases resistivity in semiconductors.

Resistivity depends on the structure of atoms, their arrangement in the lattice and on how strongly the valence electrons are bound to its nuclei. Thus, it is material-specific property.

Resistivity find its applications in selection of materials for electrical wiring (low resistivity materials), designing heating elements (high resistivity materials), and studying material properties in electronics.

Resistance is inversely proportional to the cross-sectional area \(A\). A thicker wire has a larger \(A\) and hence lower resistance.

Affect of temperature varies with materials. For metals, resistivity increases with temperature. For semiconductors, resistivity decreases as temperature increases.

Possible sources of error include loose or faulty connections, parallax error in reading voltmeter or ammeter, resistance of connecting wires or measuring instruments, and
inaccurate calibration of devices.

Minimizing errors can be done by using properly calibrated instruments, ensuring all connections are tight and secure, taking multiple readings and use their average. Resistance in connecting wires can be reduced by using thick copper wires