# Force between the plates of a capacitor when a dielectric slab is added

• avicenna

#### avicenna

Say there are two parallel plates separated by a small fixed distance d and charged +q, -q. The force attracting the plates is F. If a solid block of dielectric (dielectric constant k) is introduced between the plates, will the force of attraction be different from F.

My answer: The electric field will be reduce by a factor of 1/k; thus the force is lesser than F.

Say there are two parallel plates separated by a small fixed distance d and charged +q, -q. The force attracting the plates is F. If a solid block of dielectric (dielectric constant k) is introduced between the plates, will the force of attraction be different from F.
Try a related question first. Instead of introducing a dielectric, reduce the separation between the plates by a factor of 2. Does the attractive force increase, decrease or remain the same?

• sophiecentaur
This thread could lead further to an interesting discussion; the Energy situation is as relevant as the Force situation.
You would need to specify whether the capacitor is connected to a voltage supply or just free-standing if you want a quantitative answer.
Work will be done when the dielectric is introduced; the dielectric would be 'pulled in', which would account for the lower PD across the plates when not connected to a supply.

• jbriggs444