Electricity Flashcards
What is current?
The rate of flow of charge (electrons) past a particular point in a circuit.
What is potential difference?
Work done per unit charge.
V = W / Q
What is power?
The rate of work done.
P = IV
What does Ohm’s law state?
If resistance is constant, then voltage is proportional to current.
What is an ohmic conductor?
A conductor that follows Ohm’s law.
What are 4 examples of a non-ohmic conductor?
- Semiconductor diode
- Filament lamp
- Thermistor
- Light-dependant resistor (LDR)
What happens to the resistance of a thermistor when the temperature decreases?
Resistance increases
What happens to the resistance of an LDR when the brightness increases?
Resistance decreases
What are Kirchhoff’s two laws?
Sum of currents flowing into a node = currents leaving the node.
Sum of p.d. in any closed loop = sum of potential drops in that loop.
What happens with voltage and current in a series circuit?
Voltage is shared.
Current is the same.
What happens with voltage and current in a parallel circuit?
Voltage is the same.
Current is shared.
What is the resistance of an ideal ammeter?
Zero
What is the resistance of an ideal voltmeter?
Infinite
What is resistivity?
(Resistance x Cross-sectional area) / Length
What is a superconductor?
If below critical / transitional temperature, resistance and resistivity is zero.
What are some examples of superconductors?
- MRI
- Particle accelerators
- Power cables
- Maglev
What does potential divider mean?
Input voltage in series circuit is split between components in the same ratio of their resistance to the total resistance.
What is a rheostat?
A type of variable resistor.
What does e.m.f. stand for?
Electromotive force
What is internal resistance?
Resistance of the cell / battery.
What is measured on the cell when the circuit switch is open?
E.m.f.
What is measured on the cell when the circuit switch is closed?
Terminal voltage
What are lost volts?
Voltage lost when current flows through a cell / battery with an internal resistance.
What does a semiconductor diode do?
Only allows current to flow in one direction.
