Question

Why does the resistance of the metal filament inside the bulb increases as the potential difference across the bulb increases

Answer 1

Explanations

• The resistance of a metal wire is given by

$\qquad\qquad \begin{aligned} \small R&= \small \frac{\rho L}{A} \end{aligned}$

• Therefore, any change in resistance due to the variations of physical quantities is according to the above equation.
• Therefore, there is no direct relationship between the change in resistance with the applied voltage.
• What may happen is, when the voltage is increased the flowing current is increased which causes a built-up heat.
• Risen-up temperature, therefore, may result in an increment of the resistance of the filament wire.
• This is very basic as for the normal conductors.