Practice question · Estimate
A capacitor of relative permittivity 1 is filled with a dielectric of at fixed charge. Set the factor by which its capacitance changes.
Estimate on a scale from Falls to zero (0) to Rises sixfold (6).
Hints
- The field and hence the voltage fall by the factor epsilon-r.
- Capacitance is charge over voltage, and the charge is unchanged, so C rises by the same factor.
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3 (answers within ±0.3 count)
Why
The field drops by , so drops threefold while is unchanged, and therefore triples. This is why practical capacitors are filled rather than left empty.
Practise Dielectrics and Polarisation
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