Homework Help: Approximation question -- How does this approximation simplify the integral?

1. Dec 4, 2014

RF_FAN

how does this aproximation reduse the integral

2. Dec 4, 2014

Staff: Mentor

Where are lambda and k_z in the integral?

The approximation simply assumes the integrand to be constant, evaluates it at the midpoint (z'=0) and multiplies it with the range z' takes.

3. Dec 5, 2014

RF_FAN

so its because r'=0 ??
then why we need
l<<lambda kz<<pi
?

4. Dec 5, 2014

Staff: Mentor

The exponential function should not change its argument too much, so kzl/r should be small compared to 1.