Current exists whenever…
there is a net flow of charge (not an electrostatic equilibrium).
DC Current from…
batteries.
SI unit of current
Ampere
By convention, the direction of current is…
The direction of the flow of positive charge.
Charge carriers: Positive or negative?
Negative
Current
The electrons in a conductor move in response to an electric field in the conductor.
vd
drift speed.
drift speed dependent on many parameters, most notably
temperature
At a higher temperature, the drift speed…
decreases - more collisions.
sigma
conductivity of metal.
rho =
1/sigma
Ohmic material
Resistance curve is linear.
Kirchoff’s Rules for Circuits
Conservation of charge: junction rule. Conservation of energy: loop rule.
Conservation of charge: junction rule
I in = I out (sums)
Conservation of energy: loop rule
The sum of the potential differences across all the circuit elements in a closed loop must be zero.
Power
Rate of energy transformation.
Units of power
Watt
Watt
Joules/Second
Series
Two circuit elements are said to be connected in series if the current, passing through one, has no option but to pass through the other.
Parallel
Two circuit elements are said to be connected in parallel if both their sides are connected with no intervening circuit elements.
