Overview
This lecture explains the current–potential difference (I–V) graph for a filament lamp, compares it to a resistor, and explains the reasons for the graph’s shape.
Resistors and Omic Conductors
- Resistors are used in circuits to control the potential difference (voltage) across components.
- For a resistor, current is directly proportional to potential difference, producing a straight-line graph through the origin.
- Such components are called omic conductors, which have constant resistance if temperature does not change.
Filament Lamps and Their Behavior
- Filament lamps contain a very fine, tightly coiled wire called a filament.
- When current passes through the filament, it gets extremely hot and emits light.
- Increasing potential difference across a filament lamp does not result in proportional increases in current.
Current–Potential Difference Graph for Filament Lamps
- The I–V graph for a filament lamp is not a straight line; it curves.
- As the potential difference increases, the current increases more slowly, showing the resistance is increasing.
- At higher temperatures, atoms in the filament vibrate more, causing more frequent collisions with electrons, increasing resistance.
- Filament lamps are not omic conductors because their resistance changes with temperature.
Key Terms & Definitions
- Omic Conductor — A component with constant resistance when temperature is constant; follows Ohm’s law.
- Filament Lamp — A lamp that produces light using a thin wire (filament) that glows when electric current passes through it.
- Current–Potential Difference (I–V) Graph — A graph showing the relationship between electric current and potential difference for a component.
Action Items / Next Steps
- Learn and be able to draw the I–V graph for a filament lamp.
- Be ready to explain why the resistance of a filament lamp increases with temperature.
- Review example questions about filament lamp resistance in the revision workbook if available.