# 9.2.4 Resistance in a Filament Lamp

### 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

• 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 current decreases, then the resistance will increase (V = IR)
• Therefore, an increase in temperature causes an increase in resistance ### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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