# Homework Help: What is the condition for the radiation term in the expression for the field B to

1. Jan 11, 2012

### blueyellow

1. The problem statement, all variables and given/known data

What is the condition for the radiation term in the expression for the field B to predominate? Express you answer as a relationship between distance r and wavelength $\lambda$.

B(r)=$\frac{\mu_{0}I_{0}\delta l}{4\pi}$sinθ ($\frac{-i\omega}{rc}$+$\frac{1}{r^{2}}$)exp[i(kr-$\omega$t)]$\phi$-hat

3. The attempt at a solution

r>>$\lambda$?
But how was this result obtained? If r>>c/omega, r>>c/(2$\pi$f), r>>$\lambda$/(2$\pi$), then how was the 2$\pi$ got rid of?

If r>>c/$\omega$, why is this the case?