Electrostatics, Ohm's Law, and Circuits

Coulomb’s Law

Force between two charges: ( F = k(q1q2/r²)

Electric Field

Force per unit charge: ( E = F/q = kQ/r² )

Electric Potential Energy

Potential energy between two charges: ( U = k(q1q2/r)

Electric Potential (Voltage)

Potential energy per unit charge: ( V = U/q = kQ/r)

Direction of Electric Field

Points away from positive charges and toward negative charges

Like Charges

Repel each other

Opposite Charges

Attract each other

Ohm’s Law

Relationship between voltage, current, and resistance: ( V = IR )

Current

Flow of positive charge (conventional current direction)

Resistance

The opposition to current flow, measured in ohms (Ω)

Power in a Circuit

( P = IV = I^2R = V²/R )

Series Circuit

Resistors add: ( Req = R1 + R2 + …); current is the same through each

Parallel Circuit

Inverse resistance adds: ( 1/Req = 1/R1 + 1/R2 ); voltage is same across each

Capacitor in Series

Inverse adds like resistors in parallel: ( 1/Ceq = 1/C1 + … )

Capacitor in Parallel

Add directly like resistors in series: ( Ceq = C1 + C2 + …)

Unit of Charge

Coulombs (C)

Unit of Current

Amperes (A)

Unit of Voltage

Volts (V)

Unit of Resistance

Ohms (Ω)

Unit of Power

Watts (W)

How to increase resistance

Increase length, decrease area, or use a material with higher resistivity