The I-V graphs of a resistor, a filament lamp and a diode, finding resistance from them, and the I-V required practical.
What you will learn
- Recognise the I-V graphs of a resistor, a filament lamp and a diode
- Find a resistance from a point on an I-V graph
- Plan and analyse the I-V characteristics practical
Three graphs to know
An I-V graph puts potential difference along the bottom and current up the side, with negative values for the supply connected the other way round.
Fixed resistor at constant temperature: a straight line through the origin. Current is directly proportional to p.d., so the resistance is constant.
Filament lamp: a curve that flattens off at both ends (an S shape), the same shape for negative p.d. as for positive. As the current grows the filament heats up and its resistance rises.
Diode: no current at all in the reverse direction (very high resistance), then a steep rise once the forward p.d. passes about 0.6 V. Current flows one way only. The p.d. where the current starts to rise is where the diode starts to conduct (let current through). Read it from the graph you are given: it is usually between 0.5 V and 0.7 V.
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Three graphs to know
- Resistance from a graph
- Required practical: I-V characteristics
- Try it: Watch an ohmic line in the simulation
8 practice questions, marked as you go; about 25 minutes in all.
Key terms
Conduct, Steeper, Less, Valid, Accurate
In this unit: Electric circuits
Circuit symbols, charge and current, V = IR, I-V graphs, series and parallel circuits, and sensing circuits with LDRs and thermistors.
- Circuit symbols, charge and current
- Potential difference and resistance
- Current-potential difference graphs
- Series circuits
- Parallel circuits
- Sensors and the resistance practical