Resistance in a Filament Lamp
- The I-V graph for a filament lamp shows the current increasing at a proportionally slower rate than the potential difference
Filament Lamp Graph
I-V characteristics for a filament lamp
- This is because:
- As the current increases, the temperature of the filament in the lamp increases
- Since the filament is a metal, the higher temperature causes an increase in resistance
- Resistance opposes the current, causing the current to increase at a slower rate
- Where the graph is a straight line, the resistance is constant
- The resistance increases as the graph curves
Resistance and temperature
- All solids are made up of vibrating atoms
- The higher the temperature, the faster these atoms vibrate
- Electric current is the flow of free electrons in a material
- The electrons collide with the vibrating atoms which impedes their flow, hence the current decreases
- So, if the temperature increases, the resistance increases
- And as the resistance increases, the current decreases
