Dielectrics and the Polarisation of Matter · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The insulator that boosts a capacitor

Science · Electricity & Magnetism · ages 19-20
Name ______________________   Date ____________

  1. A slab with dielectric constant kappa fills the field region E0. What is the net field inside?

    • E0 times kappa
    • E0 over kappa
    • E0 plus kappa

  2. What happens inside an insulator placed in an electric field?

    • Dipoles align and their field opposes the applied one
    • Free charges stream across the slab
    • Nothing at all responds

  3. How do polar and nonpolar molecules differ in a field?

    • Polar rotate owned dipoles; nonpolar grow induced ones
    • Nonpolar rotate owned dipoles; polar grow induced ones
    • Both release free charges

  4. The same capacitor stays wired to a battery, fixing V. You slide in the kappa 2 slab. What happens?

    • Stored charge stays the same
    • Charge flows off the plates
    • Extra charge flows on, raising stored charge

  5. An isolated capacitor holds fixed charge. You slide in plastic with kappa 2. What happens to the voltage?

    • It doubles
    • It halves
    • It stays the same

  6. A dielectric reshapes the field by letting free charges move through it.

    Circle one:   True   False

  7. Why does sliding the slab between the plates change the voltage at fixed charge?

    • The plates move closer together
    • The aligned dipoles oppose the field, cutting the net field for the same Q
    • Free electrons leave the plates

  8. Kim says sliding in the slab cuts the capacitance by kappa. What is wrong?

    • Capacitance multiplies by kappa; the voltage falls instead
    • Capacitance ignores the slab entirely
    • The slab changes the plate area
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Answer key

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

The insulator that boosts a capacitor W1-mt_OYRr_k3IW6-s1

  1. E0 over kappa · The opposing dipole field cuts E0 by the factor kappa.
  2. Dipoles align and their field opposes the applied one · Aligned dipoles build an opposing field that cuts the net one.
  3. Polar rotate owned dipoles; nonpolar grow induced ones · Polar molecules own dipoles; nonpolar ones borrow them from shifted clouds.
  4. Extra charge flows on, raising stored charge · V fixed with doubled C pulls on doubled Q.
  5. It halves · Same Q with twice the capacitance needs half the volts.
  6. False · Only bound dipoles align; no free charges travel.
  7. The aligned dipoles oppose the field, cutting the net field for the same Q · Less net field across the same gap means less voltage.
  8. Capacitance multiplies by kappa; the voltage falls instead · C grows by kappa while V absorbs the drop at fixed Q.
Worksheet · LightMySky