# Current

• Current and charge must be conserved item.
• The current is the amount of charge per second
• units: C/s = A
• Direction of current is direction of positive charges’ motion

# Kirchhoff’s Rules (Or “How to analyze a circuit”)

• The amount of current going into a junction must equal the amount going out (otherwise it would pile up)
• The changes in potential around any closed loop is zero

# Circuit Elements

## Batteries

• The potential drop across a battery is fixed

## Resistors

• Resistors dissipate electrical potential energy into something else (heat, motion, light, etc.)
• The potential drop across a resistor is related to the current and resistance

• The resistance is fixed by the material, units:

• The potential drop across a wire is zero ()

## Capacitors

• A capacitor is two pieces of metal that don’t touch
• Capacitors store charges separated. Therefore, they store energy
• The capacitance is a property of the geometry of the plates
• The potential drop across a capacitor is related to the charge and the capacitance:

• For parallel plates

• Units

# Power

• The power provided/stored/dissipated by a circuit element is

• Must do element-by-element