Dielectric Strength

1. Dec 5, 2009

theman408

I know it has to do something with the Breakdown voltage but i've looked everywhere on my book and i have no idea how to calculate it.

2. Dec 5, 2009

theman408

i would reallly like to know, without this i can't do my problem.

this is all i need.

3. Dec 5, 2009

rock.freak667

What is the problem exactly?

4. Dec 5, 2009

theman408

It's two parallell plates which 12 volts are applied, i already calculated the capacitance with the Area and distance between the plates. Now i must calculate it's dielectric strength.

5. Dec 5, 2009

rock.freak667

The capacitance depends on the area, dielectric strength and distance. How did you find C with only two?

6. Dec 5, 2009

theman408

Sorry, forgot to specify. i used the formula of

C= eoerS/D

where Eo is the permitivity constant, Er is the relative permitivity which was given in the exercise, S is the area of the surface and D is the distance between the plates.

The Problem is which is the min. dielectric strength that it has.

7. Dec 5, 2009

rock.freak667

but the dielectric strength depends on the fluid between the plates. The dielectric strength which is given by e0er

8. Dec 5, 2009

theman408

What would the min. value?

would i have to calculate a new er?

9. Dec 5, 2009

theman408

and it doesn't specify the fluid, which is kinda of the point, for us to calculate it without looking at the table.

10. Dec 5, 2009

rock.freak667

What you are doing sort of looks counter-intuitive to me.

$$C=\frac{\epsilon_0 \epsilon_r A}{d}$$

you used that to get C, yes I get that. You know, A,d,ε0 and εr. You find C.

What you are asking is to get ε (or ε0εr) for the same C, A and d. You will just get back what you used above. Am I missing something ? Does A,d or A change?

11. Dec 6, 2009

theman408

Exactly thats the formula but what im asked to calculate is the min. dielectric strength V/M.

They give us Er which i looked up on a table and it's the Dielectric constant of Barium titanate.

12. Dec 6, 2009

rock.freak667

V/M ? as in volt per metre as units? If that is the case then those units mean you need to find the electric field strength. Which is simply E=V/d

13. Dec 6, 2009

theman408

Yep, it's positive right?

14. Dec 6, 2009

rock.freak667

I would think so.

15. Dec 6, 2009

theman408

The table in the back of my book that gives the different dielectric strengths it's unit is expressed x10^6 V/M and with that formula it only gives me kv/m.

16. Dec 6, 2009

rock.freak667

What is the distance between the plates?

17. Dec 6, 2009

theman408

2x10^-3 m

18. Dec 6, 2009

rock.freak667

Well the dielectric strength gives the maximum electric field that can be applied before breakdown occurs. I doubt 12V is the maximum voltage, but that would be how to find it.

19. Dec 6, 2009

theman408

Im in the crossroads in using this formula E= Q/EoArea that yields 7.2 x10^6 V/M or E= V/D that yields 6 kv/M

A= 1m^2
Q= 63.72 uC
D= 2mm
V= 12 V

all the dielectric strength values in the table appear in x10^6 V/M