In a circuit, current is the flow of charge.
It can be measured in coulombs per second where 1 C / s = 1 amp.
The electrons actually flow from negative to positive
Current (A) = Charge (C) / time (s) I = Q / t
They are vibrating about randomly inside the metal very quickly but they drift though the wire very slowly.
Current is large cos there are a LOT of electrons flowing, not cos they travel quickly.
Amount of energy transferred per coulomb is called the voltage or potential difference (p.d.)
1 Volt = 1 Joule per Coulomb (1JC )
Voltage (V) = Energy Transferred (J) / Charge (C) V = W / Q
Through a bulb this energy is transferred into other forms, e.g. heat and light.
Power (W) = Energy Transferred (J) / time (s) P = W / t
Greater the resistance then the bigger the voltage needed to make a certain current flow.
Resistance (Ohms) = Voltage (V) / Current (A) R = V / I
Components can vary, e.g. the resistance of a bulb gets bigger when the bulb gets hotter
When resistance is fixed then voltage and current are proportional.
Conductance (S) = Current (A) / Voltage (V) G = I / V