Yr 12 - Energy Power & Resistance Flashcards
Kirchhoff 1st Law
Current flowing into a node (or Junction) is equal to the current flowing out of it
Kirchhoff 2nd Law
Total EMF is equal to the total current and resistance within the circuit
Potential Difference
Energy transfer per unit charge
Current
Rate of flow of charge
Resistance
The opposition to the flow of charge
Semi-Conductor
A material that allows partial charge to flow.
- Mid charge carrier density
Conductor
A material that allows charge to flow freely
- High charge carrier density
Charge Carrier
- Particle that is free to move, carrying an electric charge
What is a Thermistor?
A (thermal resistor). R decrease as temp increase.
NTC?
Negative Temperature coefficient
- Where resistance decreases as temperature increases.
Why does a semi-conductor become more conductive when heated?
Electrons escape and therefore more charge carriers available.
Resistance Relationships with length and area
R ∝ L (more collisions due to L increasing)
R ∝ 1/A (less collisions as charge follows path of least resistance)
What is resistivity?
Measure of the resisting power of a material.
- Changes with different materials
- Constant at constant temperature
How to measure the resistivity of a wire.
- Voltmeter in parallel
- Amp meter in series
- Change the lengths of wire
- Adjust power slowly so same current flowing through wire.
- Resistivity changes with temperature
- Plot Resistance-Length graph to calculate resistivity.
What is 1KWH?
1 Kilowatt of power usage per hour
1KWH = 1000W x 3600s = 3.6x10^6 J
