Magnetic energy

1. Nov 21, 2009

tomfrank

1. The problem statement, all variables and given/known data
Considering the earth magnetic field, I need to find the magnetic energy stored in our classroom.

2. Relevant equations

U= (1/2*$$\mu$$) B2

3. The attempt at a solution

Any suggestions?

2. Nov 21, 2009

kuruman

Your expression is the energy density (Joules/m3). How many cubic meters is the volume of your classroom?

3. Nov 22, 2009

tomfrank

around 300 cubic meters

4. Nov 22, 2009

ideasrule

Do you still need help? You can find the value of B online, so you can find the energy density using your formula.

5. Nov 22, 2009

tomfrank

so once I have B i just put in the equation and solve for U

and then I multiply U by the volume of the classroom?

where do I found accurate value of the magnetic field of the Earth online?

6. Nov 22, 2009

kuruman

7. Nov 22, 2009

tomfrank

U= (1/8*pi*10^-7 ) *(54,191.9 nT )^2 = 0.001168500483 (J/m^3)

now

U*Volume= Energy classroom = 0.00117 (J/m^3)* 300 = .35 Joule

is this right?

8. Nov 22, 2009

kuruman

I didn't put in the numbers, but it looks right.

9. Nov 23, 2009

thank you