3.1 Temperature dependence of resistance

1.1 Current in different situations

2.1 Expression for drift velocity
2.2 Mobility $\left( \mu \right)$

3.1 Temperature dependence of resistance
3.2 Resistivities of different materials
3.3 Limitations of ohm's law

5.1 Combination of cells

6.1 Maximum power transfer theorem
6.2 Kirchhoff's law

9.1 Comparison of emfs of two primary cells.
9.2 Determination of Internal resistance of a cell using potentiometer

10.1 Ammeter
10.2 Voltmeter

When temperature of a conductor is increased, the thermal energy of free electron increases, due to which electrons collide more frequently with the atoms or ions of the metal. Thus, the relaxation time $(\tau)$ decreases and resistance $(R)$ increases.

Resistance of conductor at any temperature $T$ is given by, $${R_T} = {R_0}(1 + \alpha T)$$

where, ${R_0}$= Resistance of conductor at $0^\circ C$ and $\alpha $= temperature coefficient of resistance

$$\alpha = \frac{{{R_T} - {R_0}}}{{{R_0}T}}$$

Unit of $\alpha $ is $^\circ {C^{ - 1}}$ or $Kelvi{n^{ - 1}}$

$\alpha $ is positive. So, ${R_T} > {R_0}$

The resistance of a conductor increases with increase in temperature.

$\alpha $ is negative. So, ${R_T} < {R_0}$

The resistance of insulator and semiconductor decreases with increase in temperature.

For alloys like nichrome, Manganin etc, $\alpha $ is very small. So, ${R_T} \approx {R_0}$

The resistance of alloys remains constant with increase in temperature.

That is why alloys are used to make Standard resistance coil.

Resistivity of metallic conductor is given by $${{\rho _T} = {\rho _0}(1 + \alpha T)}$$