Dielectrics
Insert materials between plates. Builds on Capacitance.
A parallel-plate capacitor is charged to 100 V by a battery, then DISCONNECTED from the battery. You now slide a thick glass slab (κ = 5) into the gap, completely filling the space between the plates.
What happens to the voltage across the capacitor?
The voltage drops to just 20 V! With the battery disconnected, charge is locked on the plates. The glass dielectric increases capacitance by κ = 5, so from Q = CV, the voltage must fall by the same factor. The dielectric’s polar molecules partially cancel the field — and the slab actually gets sucked into the gap!
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Slide the dielectric in and out of the gap. Watch the voltage and field strength change in real time. Toggle between ‘battery connected’ and ‘battery disconnected’ modes to see how the same action produces completely different results!
C = κε₀A / d
The dielectric constant κ multiplies the capacitance. Glass has κ ≈ 5, water has κ ≈ 80, and vacuum is exactly 1. Higher κ means more charge stored at the same voltage.
Those tiny components on circuit boards use ceramic dielectrics with κ up to 10,000, packing huge capacitance into millimeter-sized packages.
LCD pixels work by rotating polar molecules in an electric field — the same polarization physics that makes dielectrics work.
Water’s enormous dielectric constant (κ ≈ 80) weakens electric forces between ions by 80×, letting it pull salts apart effortlessly.
Transformer oil, rubber gaskets, and porcelain insulators all exploit dielectric properties to prevent dangerous electrical breakdown.
“A dielectric doesn’t add charge — it weakens the field. But that simple act multiplies capacitance, changes voltage, and even creates mechanical forces. The slab wants to be pulled in.”
Dielectric Explorer
Slide different dielectric materials between capacitor plates. Compare vacuum, glass, ceramic, and water. Switch between battery-connected and disconnected modes to see how the same dielectric produces opposite effects on charge and voltage.
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Start with the battery disconnected and slowly insert the glass slab. Watch the voltage plummet while charge stays constant. Now reconnect the battery and try again — this time the voltage stays fixed but charge rushes in from the battery! Try water (κ = 80) for a dramatic effect. Watch the force meter — the slab is always pulled inward.
Dielectrics weaken the internal field by polarization, boosting capacitance by κ. The outcome — whether charge increases or voltage decreases — depends entirely on whether the battery is connected. Either way, the dielectric gets pulled in by the field.