What is the potential difference between the plates after a sheet of teflon is inserted between them?

Capacitance C of a parallel plate capacitor is C=Q/V, where Q is the charge on the plates and V is the potential difference between the plates. The potential of the capacitor is then: V=Q/C.

The capacitance C is given by the equation C=k*ε₀*(A/d) where k is the dielectric constant, ε₀ is the permittivity of free space, A is the surface of the plate and d is the distance between the plates.

For vacuum and air, k=1 so the capacitance is C=ε₀*(A/d).

But when we insert a dielectric between the plates like teflon which has k=2.1 at T=20°C the capacitance becomes:

C₁=k*ε₀*(A/d)=2.1*ε₀*(A/d)=2.1*C. 

We can see that the capacitance increases by k=2.1 which is the dielectric constant of teflon. 

So the voltage V becomes:

V₁=Q/C₁=Q/(2.1*C)=(1/2.1)*(Q/C)=(1/2.1)*V=0.48*V.

V₁=0.48*V.

Potential difference decreases by 0.48 because we inserted teflon between the plates. 

The radiation of the fire causes the saucepan to heat up. the conduction of the saucepan then to distribute the heat over the saucepan and to give heat to the water. the convection of the water distributing the heat within the water, till all the water is boiling