Conductors, Shielding and Surface Charge · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Quiet inside a conductor

Science · Electricity & Magnetism · ages 18-20
Name ______________________   Date ____________

  1. The electric field inside a conductor at rest is zero.

    Circle one:   True   False

  2. What makes copper an excellent conductor?

    • Each atom lends a free wandering electron
    • Its atoms never lose any electrons
    • It melts at a very high temperature

  3. Where does excess charge sit on a resting conductor?

    • Spread evenly through the volume
    • On the outer surface
    • Only at the exact center

  4. How does the field just outside a charged conductor point?

    • Along the surface, sideways
    • In circles around the conductor
    • Perpendicular to the surface

  5. A hollow shell holds a positive charge at its center. What sits on the inner surface?

    • An equal negative charge
    • An equal positive charge
    • No charge at all

  6. Why are riders safe inside a car struck by lightning?

    • Rubber tires absorb the whole strike
    • The metal shell shields the interior from the field
    • Lightning never actually hits cars

  7. A neutral shell surrounds a positive center charge. What lands on its outer surface?

    • Positive charge matching the center, since the inner surface took the negative
    • Negative charge matching the center
    • Nothing, since the shell started neutral

  8. A student draws field lines running through the metal wall of a resting shell. What is the error?

    • Field lines cannot cross any surface
    • The wall interior must be field free at rest
    • Shells always double the field inside walls
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Answer key

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

Quiet inside a conductor W1-mt_2zmzTE-dgL-s1

  1. True · Rest means no charge moves, so no inside field can remain to push them.
  2. Each atom lends a free wandering electron · Those conduction electrons drift from atom to atom whenever pushed.
  3. On the outer surface · Mutual repulsion drives extra charge outward until it reaches the surface.
  4. Perpendicular to the surface · Any sideways part would drag surface charge along, which rest forbids.
  5. An equal negative charge · The center charge pulls opposite charge inward, and the metal between stays field free.
  6. The metal shell shields the interior from the field · Charge stays on the outer skin and the inside field stays zero.
  7. Positive charge matching the center, since the inner surface took the negative · The shell as a whole stays neutral, so outer positive balances inner negative.
  8. The wall interior must be field free at rest · Lines through the metal would mean a field pushing free charges there.
Worksheet · LightMySky