How to Prepare for Assessment 4: Induction, AC Circuits, and EM Waves

This assessment focuses on understanding and reasoning, not memorization or speed. It covers Chapters 13–16, with major ideas from induction, inductance, AC circuits, and electromagnetic waves.

Start early. Give yourself time to draw diagrams, practice graphs, and explain the physics in words. You do not need to master everything in one sitting.

What this assessment is testing

The main ideas are:

using Faraday’s Law to connect changing magnetic flux with induced EMF
using Lenz’s Law to determine the direction of induced current and induced magnetic field
connecting induction to circuits, forces, motion, and energy
understanding how inductors resist changes in current and store energy
analyzing LR and LC circuits, including exponential behavior and oscillations
using phasors, impedance, resonance, and power in AC circuits
explaining how electromagnetic waves connect changing electric and magnetic fields

Most important: A correct final answer without reasoning will not receive full credit. Show your setup, your diagrams, your graphs, and your thinking.

How to study

Practice drawing the situation before writing equations.
For induction problems, ask: What magnetic flux is changing?
Use Lenz’s Law before calculating current direction.
For circuits, identify whether the behavior is steady, changing, oscillating, or driven by AC.
For graphs, focus on the correct shape, labels, and physical meaning.
For AC circuits, practice drawing phasor diagrams and identifying resonance.
For EM waves, practice drawing the electric field, magnetic field, and direction of travel.

Induction and Inductance

Main topics: magnetic flux, Faraday’s Law, Lenz’s Law, induced current, induced electric fields, inductors, LC circuits, and LR circuits.

Important ideas

Magnetic flux depends on magnetic field strength, area, and angle.
Faraday’s Law says changing magnetic flux creates an induced EMF.
Lenz’s Law says the induced effect opposes the change that caused it.
Inductors resist changes in current and store energy in magnetic fields.
LR circuits have exponential current growth or decay.
LC circuits involve energy oscillating between an electric field and a magnetic field.

Problems to practice

A loop entering or leaving a magnetic field.
A sliding conducting bar on rails.
Finding the direction of induced current using Lenz’s Law.
Finding induced EMF and induced current.
Finding magnetic force on a current-carrying wire.
Sketching current vs. time in an LR circuit.
Comparing LR circuits to RC circuits from earlier in the course.

Physics 1 connections

Newton’s Laws: magnetic forces can change motion.
Energy conservation: mechanical energy can become thermal energy.
Graphs: exponential growth and decay.
Oscillations: LC circuits behave like simple harmonic motion.

Quick Check: Induction and Inductance

Which skill is most important for induction problems on this assessment?

Identifying what magnetic flux is changing, then using Lenz’s Law to determine the direction of the induced effect.: Correct: Yes. Start with what changes, then decide what the induced current or field does to oppose that change.
Memorizing whether every induced current is clockwise or counterclockwise.: Not quite. Current direction depends on the situation. Use Lenz’s Law and the right-hand rule each time.

AC Circuits

Main topics: AC voltage and current, phasors, resistors, capacitors, inductors, RC filters, RLC circuits, resonance, and power.

Important ideas

AC voltage and current change sinusoidally with time.
In a resistor, voltage and current are in phase.
In a capacitor, current leads voltage.
In an inductor, voltage leads current.
Impedance is the AC version of resistance.
At resonance, current is largest in a series RLC circuit.

Problems to practice

Finding resonance frequency.
Finding impedance in an RLC circuit.
Finding rms current and average power.
Drawing phasor diagrams.
Sketching current amplitude vs. frequency.
Explaining why voltage across a capacitor or inductor can be larger than the source voltage.

Physics 1 connections

Resonance in RLC circuits is like resonance in a mass-spring system.
Energy moves back and forth between electric and magnetic forms.
Damping reduces the size of oscillations.

Quick Check: AC Circuits

What should you be able to explain about a series RLC circuit at resonance?

Current is largest, impedance is smallest, and energy moves back and forth between the capacitor and inductor.: Correct: Yes. Also connect this to resonance in Physics 1 oscillators.
Current is smallest because the capacitor and inductor both block the current.: Not quite. At resonance, the capacitor and inductor effects cancel in the impedance, so current is largest.

Electromagnetic Waves

Main topics: Maxwell’s Equations, electromagnetic waves, wave speed, electric and magnetic field directions, wavelength, frequency, and energy transport.

Important ideas

Changing electric fields create magnetic fields.
Changing magnetic fields create electric fields.
Electric and magnetic fields can sustain each other as a wave.
EM waves do not need a material medium.
Light is an electromagnetic wave.
The electric field, magnetic field, and direction of travel are all perpendicular to each other.

Problems to practice

Finding wavelength from frequency.
Finding magnetic field amplitude from electric field amplitude.
Drawing the electric field, magnetic field, and wave direction.
Sketching sinusoidal wave graphs.
Explaining how Maxwell’s Equations connect electricity and magnetism.

Physics 1 connections

Wave speed, frequency, and wavelength.
Sinusoidal graphs.
Energy carried by waves.

Quick Check: Electromagnetic Waves

In an electromagnetic wave, how are the electric field, magnetic field, and direction of travel related?

They are all perpendicular to each other, and the electric and magnetic fields oscillate together.: Correct: Yes. You should be able to draw all three directions on a coordinate-axis sketch.
The electric and magnetic fields point in the same direction as the wave travels.: Not quite. The fields are transverse: they are perpendicular to the direction the wave travels.

Review and Synthesis

Expect problems that combine several ideas at once.

Faraday’s Law with circuits.
Lenz’s Law with force directions.
Magnetic force with Newton’s Laws.
Inductors with energy conservation.
RLC resonance with Physics 1 oscillations.
EM waves with earlier wave concepts.

Quick Check: Review and Synthesis

What makes this assessment different from a single-topic quiz?

Problems may combine induction, circuits, forces, energy, oscillations, waves, and earlier Physics 1 ideas.: Correct: Yes. Be ready to connect topics instead of treating each chapter as separate.
Each problem will only use one equation from one chapter.: Not quite. Expect multi-step problems that ask you to combine ideas and explain your reasoning.

Graphing and diagram skills

You should be able to make clear, labeled sketches. They do not need to be artistic, but they must show the physics.

Graphs to practice

Current vs. time in an LR circuit.
Induced EMF vs. time.
Velocity vs. time for a sliding bar slowing down due to magnetic drag.
Current amplitude vs. frequency for an RLC circuit.
Electric and magnetic field waves vs. position or time.

Diagrams to practice

Direction of induced current.
Direction of induced magnetic field.
Magnetic force on a current-carrying wire.
Phasor diagrams for AC circuits.
Electric field, magnetic field, and propagation direction for EM waves.

Quick Check: Graphs and Diagrams

What makes a graph or diagram useful on this assessment?

It clearly shows the physics: direction, shape, labels, and important features, even if it is not artistic.: Correct: Yes. A useful sketch communicates your reasoning.
It must be perfectly drawn and exactly to scale.: Not necessary. Focus on correct physical meaning, not artistic perfection.

Problem-solving strategy

Draw the situation. Label fields, currents, forces, motion, and directions.
Ask what is changing. Is magnetic flux changing? Is current changing? Is energy moving from one form to another?
Use direction rules carefully. Use Lenz’s Law and right-hand rules before calculating.
Choose the right equation. Do not start with formulas until you understand the physical situation.
Check the units. Make sure your answer has the correct units.
Explain your answer. A short explanation can show that you understand the physics.

Quick Check: Problem Solving

What should you usually do before choosing an equation?

Draw the situation, identify what is changing, and determine directions using Lenz’s Law or right-hand rules.: Correct: Yes. The equation should come after the physical setup.
Look for the equation with the most variables from the problem statement.: Not quite. Matching variables is not enough. First understand the physics of the situation.

Most important equations

Magnetic flux: Φ_B = BA cosθ
Faraday’s Law: ε = -dΦ_B/dt
Motional EMF: ε = Bℓv
Ohm’s Law: I = ε/R
Magnetic force on a wire: F = IℓB
Energy in an inductor: U = ½LI²
LR time constant: τ = L/R
RLC resonance: ω₀ = 1/√LC
Wave speed: c = fλ
EM wave field relation: E = cB

Quick self-check

Can I identify what magnetic flux is changing?
Can I use Lenz’s Law to determine current direction?
Can I connect induced current to magnetic force?
Can I explain where energy goes in an induction problem?
Can I sketch current growth and decay in an LR circuit?
Can I draw a phasor diagram for an AC circuit?
Can I identify resonance in an RLC circuit?
Can I draw the electric field, magnetic field, and travel direction for an EM wave?
Can I connect this unit to waves, energy, oscillations, and Newton’s Laws from Physics 1?

If any answer is “not yet,” that just tells you where to focus next.

Final reminders

Practice by hand when you can.
Try a problem first before looking at a solution.
Focus on reasoning and setup, not just the final answer.
Use resources, but be ready to explain your thinking clearly.
For every major problem, ask yourself: What changes? What direction? Where does the energy go? What would the graph look like?

Friendly reminder: This assessment is meant to help you demonstrate what you understand. Clear diagrams, clear graphs, and clear reasoning matter.