# Homework Help: Simple electric flux through tetrahedron problem

1. Feb 1, 2012

### kirby2

A tetrahedron has an equilateral triangle base with 20-cm-long edges and
three equilateral triangle sides. The base is parallel to the ground and a
vertical uniform electric ﬁeld of strength 200 N/C passes upward through
the object.
(a) What is the electric ﬂux through the base?
(b) What is the electric ﬂux through each of the three sides?

ATTEMPT:

for part a i used flux=EA. for A i used BH/2 and got .0173. i multiplied that by 200 and got 3.46 m^2/C. can someone verify this is correct?

for part b i just divided that number by 3 because the total flux in the sides must equal that of the base so i got -1.1533m^2/C. i think the sign is negative because it must have the opposite sign of the base. is this right?

2. Feb 1, 2012

### SammyS

Staff Emeritus
I agree with the magnitudes.

What is the convention for the sign of flux?

3. Feb 2, 2012

### kirby2

the convention is positive sign?

4. Feb 2, 2012

### SammyS

Staff Emeritus
For a closed surface, what direction is positive? Inward or Outward ?

5. Feb 2, 2012

### kirby2

for a closed surface outward is positive

6. Feb 2, 2012

### SammyS

Staff Emeritus
Good !

Then the flux through the base is negative, correct?

7. Feb 2, 2012

### kirby2

yes. and the sides are positive. thank you

8. Apr 9, 2013

### Mandaz

a) -3.464 Nm^2/C

b) 1.2 Nm^2/C