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Re: dielectric constant



>A curious number can be found in many tables of dielectric constant,
the DC dielectric constant of that terribly polar material, water.
Sears & Zemansky give that number as 81, larger by far than any other
in their table. Now I am old enough that I have made capacitors for
RF purposes by stacking tinfoil and glass plates (K = 5 or so). Water
would have been nice to try, but I suspect it would have posed great
practical difficulties had I been foolish enough to do so.

Can anyone think of a phenomenon which demonstrates water's very high
dielectric constant? I do know that demonstrating capacitors at high
voltages can be very dangerous, but does anyone know a good demo?

Leigh


A thin rectangular plastic cell is placed between two capacitor plates and
the capacitance is noted. Then fill the cell with water while it's still
sitting between the plates and watch the capacitance go way up! Wolfgang

Thanks, Wolfgang. I've thought of a variant on that which I will try.
I'm glad someone has seen this done.

After writing the paragraph above I went down to the demonstration
room where my colleague Jeff Rudd keeps lots of sealing wax and string
handy. In no time flat we concocted a capacitor which is an adaptation
of Wolfgang's suggestion. It wasn't spectacular (I had hoped it would
be), but the capacitance increased by thirty percent when the water
was added. I will post details, with photos on my web site, tomorrow.

Leigh