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.