Circuits Flashcards
Charge
Charge flow = current x time
Potential Difference
Current x resistance
Fixed resistor
The current is directly proportional to the potential difference across the resistor. The resistance always stays constant.
Filament lamp
The resistance of a filament lamp increases as the temperature increases. (So resistance increases as current and potential difference increases - shown by the curve flattening out.)
Diode
The current through a diode flows in one direction only. The graph of current against potential difference is a steep curve. The resistance decreases as current and PD increase. The diode has a very high resistance in the opposite direction.
Thermistor
eg Thermostat, heat activated fire alarm, boiler
Resistance decreases as temperature increases.
LDR
eg Street lamp, car lights
The resistance of an LDR decreases as light intensity increases.
Current in series
Stays the same in every component.
PD in series
Total is shared between different components.
Resistance in series
Is the sum of the components = R^1+R^2…
Potential difference in parallel
PD across each component is the same
Current in parallel
Sum of currents through separate components.
Resistance in parallel
Total resistance of two resistors is less than the resistance of the smallest individual resistor.
