EMI

Electromagnetic Induction

Use: Notes + Revision

Electromagnetic Induction

Basics

Change in magnetic flux → induced emf
Flux: Φ = B A cosθ
Induced emf exists only when flux changes

Faraday’s Law

EMF

ε = − dΦ/dt

Negative sign from Lenz’s Law
Magnitude depends on rate of change of flux

Lenz’s Law

Direction

Induced current opposes cause of change
Energy conservation principle
Helps in finding direction of current

Motional EMF

Rod

ε = B l v

Rod moving in magnetic field
Depends on velocity and field

Induced Current

Ohm

I = ε / R

Depends on resistance of circuit
Higher R → lower current

Eddy Currents

Effects

Circulating currents in bulk conductors
Cause heat loss
Reduced using laminations

Self Induction

L

ε = − L dI/dt

Opposes change in current
L = inductance

Mutual Induction

M

ε = − M dI/dt

Between two coils
Used in transformers

Alternating Current

AC

I = I₀ sin(ωt)

Changes direction periodically
Frequency: f = ω/2π

RMS Values

Effective

Irms = I₀ / √2

Vrms = V₀ / √2

Used in power calculations

Pure Resistor

R

Voltage and current in phase
Power factor = 1

Pure Inductor

L

Current lags by 90°
No energy loss (ideal)

Pure Capacitor

C

Current leads by 90°
No energy loss (ideal)

Impedance

Z

Z = √(R² + (XL − XC)²)

XL = ωL
XC = 1 / ωC

Resonance

RLC

ω₀ = 1 / √(LC)

XL = XC
Impedance minimum
Current maximum

AC Power

Power Factor

P = Vrms Irms cosφ

cosφ = power factor
Maximum when cosφ = 1
Low power factor → energy loss