# Electric field of a disk & u-substitution

## Homework Statement

Calculate the electric field at point P (refer to visual):

## Homework Equations

I follow everything - except how the limits of integration for the u-integral (
) are arrived at?

## The Attempt at a Solution

u=x2 is the smallest value u can have, and u=x2+R2 is the greatest value u can have?

## Answers and Replies

TSny
Homework Helper
Gold Member
The lower limit of the u integration should correspond to the lower limit of the r integration (r = 0). So, the lower limit of the u integration is the value of u when r = 0. Similarly for the upper limit.

Very helpful - thank you!