Electricity
Quantities
- energy
- capacity to do work
- potential energy depends on position (includes chemical and phase changes)
- kinetic energy depends on motion (includes thermal energy)
- total energy is conserved during interactions
- symbol: E
- SI unit: Joule, J
- power
- energy per unit of time
- symbol: P
- SI unit: Watt, W (Joules/second)
- charge
- measure of electrical interaction, may be positive or negative
- charges of opposite sign attract, charges of same sign repel
- symbol: Q
- SI unit: Coulomb, C
- proton charge: e = 1.60x10-19 C
- electron charge: -e = -1.60x10-19 C
- current
- rate at which charge moves
- symbol: I
- SI unit: Ampere, A (Coulombs/second)
- voltage
- electrical potential energy per unit of charge
- symbol: V
- SI unit: Volt, V (Joules/Coulomb)
- resistance
- ability to reduce movement of charge
- symbol: R
- SI unit: Ohm, Ω (Volts/Ampere)
- impedance (symbol: Z) is the time-varying generalization of resistance
- capacitance
- ability to store charge
- symbol: C
- SI unit: Farad, F (Coulombs/Volt)
- inductance
- ability to oppose change in current
- symbol: L
- SI unit: Henry, H (J⋅C2/s2)
- Prefixes (multipliers)
| name |
SI symbol |
SI value |
| exa |
E |
1018 |
| peta |
P |
1015 |
| tera |
T |
1012 |
| giga |
G |
109 |
| mega |
M |
106 |
| kilo |
k |
103 |
| milli |
m |
10-3 |
| micro |
μ |
10-6 |
| nano |
n |
10-9 |
| pico |
p |
10-12 |
| femto |
f |
10-15 |
| atto |
a |
10-18 |
Time
- DC
- direct current, does not change with time (approximately)
- AC
- alternating current, does change with time
- frequency
- for periodic changes, number of cycles per second
- symbol: f or ν
- SI unit: Hertz, Hz (cycles/second)
Relationships
- resistance
- V=I⋅R
- capacitance
- V=Q/C
- inductance
- V=L⋅dI/dt
- energy
- E=C⋅V2/2
- E=L⋅I2/2
- power
- P=I⋅V
- P=I2⋅R
Materials
- conductor
- freely-moving electrons carry current
- typically aluminum or copper, very low resistivity
- used to carry current with low voltage drop
- insulator
- tightly-bound electrons cannot carry current
- typically plastics or ceramics, very high resistivity
- used to prevent current flow
- semiconductor
- excess electrons in N-doped crystal lattice can carry current
- missing electrons (holes) in P-doped crystal lattice can carry current
- typically silicon with various doping agents
- used to control currents