# B-field from E-field

1. Homework Statement

E = 20 cos($$\omega$$t-50x) $$\widehat{y}$$ find H in free space?

2. Homework Equations

I used ($$\nabla$$ X E ) = -dB/dt , and then integrated that expression with respect to t , for some reason I am getting an incorrect answer ?!

3. The Attempt at a Solution

the correct answer is H = 0.4 w*(eps) *cos($$\omega$$t-50x) $$\widehat{z}$$

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#### Pythagorean

Gold Member
I used ($$\nabla$$ X E ) = -dB/dt , and then integrated that expression with respect to t , for some reason I am getting an incorrect answer ?!

3. The Attempt at a Solution

the correct answer is H = 0.4 w*(eps) *cos($$\omega$$t-50x) $$\widehat{z}$$

remember that H and B are not the same.

D = eps*E
and
H = B/mu

also:

( $$\nabla$$ X H ) = -dD/dt

or for linear media:

( $$\nabla$$ X B ) = mu*eps*dE/dt

also remember that the curl pertains to spatial, not temporal derivatives.

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