Faraday's Law & Lenz's Law – AP Physics C E&M | ShowMeClass

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Faraday's Law & Lenz's Law

AP Physics C E&M · Unit 6: Induction

Learning Objectives

Apply Faraday's law: EMF = -dΦ/dt

Calculate magnetic flux Φ = BA cosθ

Apply Lenz's law to find induced current direction

Analyze bar sliding on rails in B-field

Key Equations

Lenz's Law

The induced current flows in a direction that opposes the change in magnetic flux that caused it.

Flux increasing → induced B opposes external B
Flux decreasing → induced B supports external B

Colors

External B-field

Induced EMF

Induced current

Flux Φ

FaradayLenzInduction

t =-

Φ =-

EMF =-

I_ind =-

Φ(t)

EMF(t)

I(t)

All

Scenario

B-field (mT) 50

N turns 10

Coil Area (cm2) 25

Resistance R (ohms) 5

Speed v (m/s) 2

Angular vel ω (rad/s) 5

Speed 1x

Faraday's Law Analysis

Quick Quiz▼

1. Faraday's law states EMF equals:

B*A -N * dΦ/dt N*B*A I*R

2. Lenz's law says the induced current:

Opposes the change in flux Supports the change in flux Is always zero Is proportional to B

3. A bar sliding on rails with velocity v in field B produces EMF:

BvL Bv/L BL/v B2vL