# 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 