Electromagnetism IElectromagnetism I

Week 8Week 8

ContentsContents

OverviewOverview Coulomb’s LawCoulomb’s Law CurrentCurrent VoltageVoltage ResistanceResistance Energy and PowerEnergy and Power ReviewReview

The Four ForcesThe Four Forces

1.1. StrongStrong

2.2. ElectromagneticElectromagnetic

3.3. WeakWeak

4.4. GravityGravity

James Clerk MaxwellJames Clerk Maxwell

First person to First person to fully formulate the fully formulate the classical laws of classical laws of electricity and electricity and magnetism.magnetism.

Maxwell’s Equations ofMaxwell’s Equations ofClassical ElectrodynamicsClassical Electrodynamics

BvEqF

Β

ε

j

t

ΕΒc

t

ΒΕ

ε

ρΕ

0

0

2

0

ElectrostaticsElectrostatics

The study of electric forces when all The study of electric forces when all charges are at rest.charges are at rest.

Every particle has a property called Every particle has a property called chargem. The charge is either chargem. The charge is either positive, or negative, or zero.positive, or negative, or zero.

Charge is always conserved.Charge is always conserved. Measured on Coulombs.Measured on Coulombs.

Coulomb’s LawCoulomb’s Law

F1 = kqQ/rF1 = kqQ/r22

F1 = - F2F1 = - F2

k = 1/4πεk = 1/4πε00

It is “sign It is “sign sensitive”.sensitive”.

Very similar to Very similar to gravitation.gravitation.

+Q

+q

F1

F2

The Electric FieldThe Electric Field

+q -q

Electric Field LinesElectric Field Lines

DefinitionsDefinitions

Current: i = q/tCurrent: i = q/t Voltage: V = E/qVoltage: V = E/q Power: P = q/t = ViPower: P = q/t = Vi Energy: E = Pt = VitEnergy: E = Pt = Vit

CurrentCurrent

I = q/tI = q/t j = I/a = q/atj = I/a = q/at AmperesAmperes

q

t

Current vs. EFCurrent vs. EF

+Q -Q

CurrentCurrent

3A

2A

1A

VoltageVoltage

V = E/qV = E/q Also called electric potentialAlso called electric potential VoltsVolts

VoltageVoltage

3V

3V

3V

ResistanceResistance

R = V/iR = V/i Ohms, Ω.Ohms, Ω.

Energy and PowerEnergy and Power

i = q/ti = q/t V = E/qV = E/q R = V/iR = V/i

E = VitE = Vit P = E/t = ViP = E/t = Vi

Electric CircuitsElectric Circuits

SeriesSeries ParallelParallel

CurrentCurrent

SeriesSeries ParallelParallel

I = I1 = I2 = I3 I = I1 + I2 + I3

VoltageVoltage

SeriesSeries ParallelParallel

V = V1 + V2 + V3 V = V1 = V2 = V3

ResistanceResistance

SeriesSeries

I = I1 = I2 = I3

V = V1 + V2 + V3

V/I = V1/I + V2/I + V3/I

V/I = V1/I1 + V2/I2 + V3/I3

R = R1 + R2 + R3

ParallelParallel

I = I1 + I2 + I3

V = V1 = V2 = V3

I/V = I1/V + I2/V + I3/VI/V = I1/V + I2/V + I3/V

I/V = I1/V1 + I2/V2 + I/V = I1/V1 + I2/V2 + I3/V3I3/V3

1/R = 1/R1 + 1/R2 + 1/R31/R = 1/R1 + 1/R2 + 1/R3

ReviewReview

Coulomb’s LawCoulomb’s Law F = kQq/r2F = kQq/r2

DefinitionsDefinitions i = q/ti = q/t V = E/qV = E/q P = q/t = ViP = q/t = Vi E = Pt = VitE = Pt = Vit

Electric CircuitsElectric Circuits SeriesSeries

I = I1 = I2 = I3I = I1 = I2 = I3

V = V1 + V2 + V3V = V1 + V2 + V3

R = R1 + R2 + R3R = R1 + R2 + R3 ParallelParallel

I = I1 + I2 + I3I = I1 + I2 + I3

V = V1 = V2 = V3V = V1 = V2 = V3

1/R = 1/R1 + 1/R2 + 1/R31/R = 1/R1 + 1/R2 + 1/R3

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MagnetismMagnetism