### Current

- Current has units of (Columbs per Second), or (Amperes)

- Current Density is the current per area

- Current measures the movement of coulombs through a wire, or a measured point on a wire.

### Charge Density

- Charge density is a property of a material
- It is based of of the amount of charges per unit m
^{3} - n = Charge Density (Given constant, property of material)
- nq = Charge per m
^{3} - If you multiply nq by speed V, it measures the charge passing through an area per unit time (Current Density)

### Resistivity

- Electrons move relatively slowly through a wire (still very fast, 2.3x10
^{-5}m/s for a copper wire) - They do so because as charges move through the wire, they bump into molecules and elements of the wire itself.

- E = Electric Field
- J = Current Density
- ρ = Resistivity

Resistivity ρ is a property of the material itself. It is measured in units of (Volt meters/Amps)

Examples

- Copper: ρ = 1.68x10
^{-8}Vm/A (Not very resistive) - Carbon: ρ = 5.00x10
^{-4}Vm/A (Some resistance) - Wood: ρ = 10
^{-4}Vm/A (a lot of resistance)

### Resistance

Resistance (R), unlike Resistivity is a property of the object itself. It is measured in units of (Ohms)

- R has a unit of ohms

and the big concept of resistance is

$ΔV=IR$### Power

Power (p) is the energy “lost” per unit time

$P=dtdw =ΔVdtdq $ $P=ΔVI$ $P=I_{2}R$ $P=ΔRV_{2} $- Power has units of {J/S} (Joules per Second) or {W}
- 60 Watts would be equivalent to 60 Joules of energy being lost per second
- Resistance creates heat, and in extreme cases, light.
- This is a dissipation of energy
- This is a consequent of work.

#### Work

Work is required to move a charge As speed is constant, Kinetic Energy never changes.