Displacement Current and Maxwell's Equations · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Fixing Ampere's law: displacement current and Maxwell's set

Science · Electricity & Magnetism · ages 20-22
Name ______________________   Date ____________

  1. Which Maxwell equation says there is no magnetic charge?

    • Gauss for magnetism
    • Faraday's law
    • The Ampere-Maxwell law

  2. A loop rings the gap of a charging capacitor. What plays the role of current through the loop?

    • Nothing at all: the loop rule simply fails there
    • The changing electric flux between the plates
    • The static charge sitting on the plates

  3. Magnetic poles always come in north-south pairs, and no lone pole has been found.

    Circle one:   True   False

  4. Changing magnetic flux rings the surrounding region with electric field. Which equation says this?

    • Gauss for E
    • Faraday's law
    • Gauss for magnetism

  5. What exactly is the displacement current term added to Ampere's law?

    • Static field times plate area
    • Conduction current divided by resistance
    • mu0 eps0 times the rate of change of electric flux

  6. How did Maxwell's set predict light?

    • They combine into a wave equation with speed 1 over sqrt(mu0 eps0)
    • They forbid any changing fields
    • They prove light needs a medium

  7. An antenna current oscillates, and a distant receiver with no wires picks up the signal. How?

    • Electrons fly through the air to the receiver
    • Accelerated charges shed linked E and B ripples that feed each other outward
    • The battery pushes current through empty space

  8. A student says the equations are fully symmetric, with lone north poles sourcing fields as usual. What is the error?

    • Symmetry is perfect: lone north poles source the field
    • The equations forbid electric charge too
    • The set has no magnetic charge source; poles always pair up
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Fixing Ampere's law: displacement current and Maxwell's set W1-mt_YR8m8TNfyy-s1

  1. Gauss for magnetism · Gauss for magnetism reports zero magnetic source.
  2. The changing electric flux between the plates · Changing E flux acts exactly like a current in the loop rule.
  3. True · Every known magnet carries both poles together.
  4. Faraday's law · Faraday links changing B flux to a ringing E field.
  5. mu0 eps0 times the rate of change of electric flux · The added term is mu0 eps0 times dPhiE/dt.
  6. They combine into a wave equation with speed 1 over sqrt(mu0 eps0) · The computed wave speed matched the measured speed of light.
  7. Accelerated charges shed linked E and B ripples that feed each other outward · Wiggled charges radiate, and the passing wave shoves the receiver electrons.
  8. The set has no magnetic charge source; poles always pair up · The magnetic Gauss law has zero source, which spoils the mirror.
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