Definition of current and unit
Rate of flow of charge
Amperes (A)
Definition and unit of potential difference
Energy per coulumb of charge
Volt (V)
What is constant for an ohmic conductor and therefore what is directly proportional?
Resistance
Current and pd
I/V graph for a filament lamp
Curve that starts steep around the the origin but gets shallower as voltage increases
What happens to resistance as temperature increases
Increases
What does the resistance/temp graph for NTC thermistor look like?
Resistance decreases as temp increases
I/V graph for an NTC thermistor
Low gradient around origin, gets steeper at edges
What do diodes do?
Only let current flow in one direction
I/V graph for a diode
X is threshold voltage
A
| /
| /
———-|—x— V
|
Resisivity of a material definition and unit
The resistance of a 1m length with a 1m^2 cross-sectional area
Ohm-metres
Why are super conductors so effective?
They have zero resistivity so no energy is lost as thermal energy
Why aren’t there more superconductors?
Normally need to be below 10K
Definition of power and unit
Rate of transfer of energy
watts(W)
What is used in a battery to make electrons move?
Chemical energy
Name for resistance inside a battery
Internal resistance
What does emf stand for, units and what does it mean?
electromotive force
measured in volts
Amount of electrical energy produced for each coulumb of charge
What is the load resistance
Total resistance of all components in the external circuit
What is terminal pd?
Energy transferred when 1 coulumb of charge flows through the load resistance
What 2 things would be equal if there was no internal resistance
terminal pd. and emf
How to work out emf of multiple cells in series
Add individual emfs
How to work out emf for cells in parallel
Same as emf for each individual cell
What is Kirchhoff’s first law:
Total current entering a junction= total current leaving it
Kirchoff’s second law:
total emf around a series circuit=sum of pds across each component
Current is series
Same at all points
