AP Physics 2: Unit 2 Variables

q

charge: property of an object (C)

n

number of fundamental charges (no units)

e

fundamental charge: charge of an electron or proton (no units) (1.6×10^-19 C)

I

current: flow of objects with charge (A or C/s)

V

electric potential: the energy that a hypothetical coulomb of charge would have at that spot (V or J/C)

∆V

electric potential difference: the change in energy that a hypothetical coulomb of charge would undergo between two spots (V or J/C)

ℰ

EMF: electromotive force; ideal potential difference of a battery (V)

R

resistance (Ω)

ι (circuits)

length of resistor (m)

A (resistor)

cross-sectional area of a resistor (m²)

ρ

resistivity: how resistive a material is (Ω*m)

σ

conductivity: how conductive a material is; inverse of resistivity ((Ωm)⁻¹)

P

power: rate of change of energy (W or J/s)

|ΔV/Δr|

the average electric field between two points in space is equal to the electric potential difference between the two points divided by the distance between the two points; electric fields point from high to low potential (V/m)

C

capacitance: the ability of a system to store electric charge (F)

κ

Dielectric constant (Capacitance multiplier; no units) (Dielectric of air is 1.00)

A (capacitance)

plate area (m²)

d (capacitance)

plate separation (m)

Uc

energy stored in the electric field of capacitor (J)

Vd

drift velocity of electrons in current (m/s)

j (j-ayyy)

Current density = current/cross-sectional area (A/m²)

P=

P=IΔV

P=

P=I²R

P=

P= V²/R