- $ d \vec{B} = \frac{\mu_0 I N d z}{2} \frac{a^2}{(a^2 + z^2)^{3 / 2}} \hat{k}$
- $\vec{B} = \frac{\mu_0 N I}{2} a^2 \int_0^L \frac{dz}{(a^2+z^2)^{3 / 2}} \hat{k}$
- $ Z = a \tan \theta $
- $ dz = a \sec ^2 \theta d \theta $
- $ (a^2 + z^2) = a^2 \sec ^2 \theta$
- $\int \frac{d z}{(a^2 + z^2)^{3 / 2}} = \int \frac{a \sec ^2 \theta d \theta}{a^3 \sec ^3 \theta}$
![image](https://temp-public-img-folder.s3.ap-south-1.amazonaws.com/sathee.prutor.images/subject-images/iitpal/image/physics-class-12-unit-04-chapter-03-more-applications-of-amperes-law-l-3_7-girkt6sx2sk-06.jpg)