# Homework Help: 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