on this cheat sheet
Everything on the GCSE Physics Circuit Components & I-V Graphs poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
What I-V characteristics are
An I-V characteristic is a graph of current (I) against potential difference (V) for a component. To obtain one, use a test circuit with a variable resistor to change V, then record I and V for each setting. Reverse the cell to test negative V.
Ohmic conductor (e.g. fixed resistor)
- The graph is a straight line through the origin.
- Current is directly proportional to potential difference.
- Resistance is constant at constant temperature - this is Ohm's law.
Interpretation: resistance is constant.
Filament lamp
- Current heats the filament, raising its temperature.
- Resistance increases with temperature, so the curve flattens at higher V.
- The graph is an S-shape through the origin.
Interpretation: resistance increases as V increases.
Diode
- Current only flows in one direction (forward bias) - the graph rises steeply for positive V.
- Very high resistance in reverse - the graph stays at zero for negative V.
- Used to rectify a.c. to d.c.
Interpretation: allows current in one direction only.
Thermistor and LDR
Thermistor:
- Resistance falls as temperature rises.
- The R-vs-T curve drops steeply.
- Used in car engine sensors and electronic thermostats.
LDR (light-dependent resistor):
- Resistance falls as light intensity rises.
- Used in automatic night lights, outdoor lighting, and burglar detectors.