Define current (I)
The rate of flow of charge
Unit for charge (Q)
- Coulomb (C)
- Often Ah or mAh in charge storage
Direction of current flow
From positive to negative
Equation for current (I)
I = Q/t
Define potential difference (voltage V)
Electrical energy per unit charge required as it move between two points on a circuit
Direction of Pd
From negative to positive
Equation for Pd
V = W/Q
Define Power (P)
The rate of energy transfer
Define ohms law
- The voltage in a circuit is directly proportional to the product of the current and resistance of the circuit
- V = IR
What is the sink
Point where energy is dissipated. e.g. components
Define a conductor
Allows electrical charge to flow freely when a voltage is applied across it
Define an insulator
Does not allow a flow of electrical charge at all
Define a semi-conductor
Partially allows flow of electrical charge
Relationship of Resistance and Temperature for pure metals
Resistance increases with Temperature
Relationship of resistance and temperature for insulating materials & carbon
Resistance decreases with temperature
resistance with temperature for small T
- Assume linear
- R = R₀ (1 + α₀T)
Resistance relating two temperatures
Rₜ₁/Rₜ₂ = (1 + α₀T₁)/(1 + α₀T₂)
Define an ideal source for dc circuits
Has no internal resistance, always producing their rated voltage no matter of current
Define non-ideal sources for dc circuits
Internal resistance causes voltage to be dependent on current as power dissipated in the source
Requirements for dc current source
must have a circuit
Define an open circuit
A circuit with no current so voltage across the terminals is the source voltage.
- E : open circuit emf
Energy conversion in battery
Convert chemical energy to electrical energy
Energy conversion in generator
Convert mechanical energy to electrical energy
Define emf (electromotive force)
the “force” applied by the source to move the charges around the circuit
