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Topic Title: capacitors,dielectrics.......help me out
Topic Summary: question on dielectric
Created On: 16 November 2010 09:00 PM
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 16 November 2010 09:00 PM
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bheka

Posts: 2
Joined: 16 November 2010

a capacitor is to be constructed so that its capacitance is 0.2micro farad and to take a p.d of 1.25kV across its terminals.The dilelectric is to be mica which after allowing a safety factor of 2 has a dielectric strenght of 50milliVolts per metre

a] find the thickness of the mica needed

b] determine the area of the plate assuming its a two plate construction
 17 November 2010 01:54 PM
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bheka

Posts: 2
Joined: 16 November 2010

unfortunately we the lecturee hasnt bn forthcoming....otherwise from study Q=CV....C=[Relative pemeativity*d]/A.........now i saw a formula which talks of capacitance per unit area which is C=E/D.........am not sure what E stands for in this equation............bt C is capacitance and D is plates separtion =thickness of dielectric
 19 November 2010 04:50 PM
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simonevans

Posts: 1
Joined: 19 March 2003

Hi,

This is reasonably straight forward.

Firstly, I'm quite sure the dielectric strength of mica is not 50 mV/m. It is more like 50MV/m so there may be a slight mistake there.

To find thickness use: E=V/d
E = 50MV/m, V = 1.25 kV

For the area use, C= eps.A/d
Use d from part a and find out what the rel. perm is for mica. Something like 7 I think. C is given in the question.

Hope that helps.
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