Dielectrics and Polarisation
Inserting a dielectric of constant K increases capacitance to KC by reducing the internal field through polarisation.
What is Dielectrics and Polarisation?
Inserting a dielectric of constant K increases capacitance to KC by reducing the internal field through polarisation.
Key formula / rule: C becomes KC; the field between the plates falls to E/K at constant charge.
Key points
- Compute capacitance and energy with a dielectric inserted.
- Explain polarisation in terms of bound charges.
Common exam trap
Applying the constant-charge result while the battery is still connected.
Definitions
- Term
Dielectrics and Polarisation
- Meaning
Inserting a dielectric of constant K increases capacitance to KC by reducing the internal field through polarisation.
- Term
Dielectrics and Polarisation — explanation
- Meaning
Bound charges appear on the dielectric surfaces and oppose the applied field. Whether the stored energy rises or falls on insertion depends on whether the battery stays connected.
Learning objectives
Compute capacitance and energy with a dielectric inserted.
Explain polarisation in terms of bound charges.
Formulae
- Key point
C becomes KC; the field between the plates falls to E/K at constant charge.
- Key point
Battery connected: V fixed, Q and U rise. Disconnected: Q fixed, V and U fall.
- Key point
Dielectric strength limits the maximum working voltage.
Prerequisites
PHY-U5-ELS-T2-S1-C2
Common mistakes
Applying the constant-charge result while the battery is still connected.
Treating the dielectric as a conductor.
Keywords
Dielectrics
Polarisation
Practice preview
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