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Current
The rate of flow of electrical charge, defined as I = ΔQ/Δt. SI unit is ampere (1A = 1C/s)
Voltage
The energy difference between two points in a circuit per charge, defined as V = W/q. SI unit is volt (1V = 1J/C)
Conventional current
A current that flows from the positive charge to the negative charge.
Electronic current
A current that flows opposite to the conventional current, from negative to positive.
Effects of electric current
Includes heating effect, magnetic effect, and chemical effect.
Electromotive force (emf)
The total energy difference per unit charge around a circuit. SI unit is volts.
Electric power supplied
Calculated as P = IV, where P is power, I is current, and V is voltage.
Ammeters
Devices that measure current, connected in series in a circuit.
Voltmeters
Devices that measure energy converted per unit charge, connected in parallel.
Electrical resistance
The ratio between potential difference and current, defined as R = V/I. SI unit is ohm (1Ω = 1V/A).
Ohm's law
States that current flowing through a piece of metal is proportional to the potential difference across it, providing temperature remains constant.
Ohmic behavior
When current and potential difference (pd) are proportional.
Non-ohmic behavior
When current and potential difference (pd) are not proportional.
Resistivity
A measure of the resisting power of a specified material to the flow of electric current.
Resistors in series
Total resistance R(total) is the sum of individual resistances: R(total) = R1 + R2 + R3 + …
Resistors in parallel
Total resistance is given by 1/R(total) = 1/R1 + 1/R2 + 1/R3 + …
Variable resistors
Resistors designed so that their resistance can be changed to a required value.
Thermistor
A resistor whose resistance depends on its temperature; typically has a negative temperature coefficient. ↑ T —> ↓ R
Light-dependent resistor (LDR)
A device whose resistance depends on the amount of light shining on it; increased light causes decreased resistance. ↑ light —> ↓ R
Current in series
is the same across the circuit
Current in parallel
is added up
Pd in series
is added up
Pd in parallel
is the same across the circuit
Note 
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