Applications of Ampere's law:

We illustrate the application of Ampere's Law with some examples.

Example 4.2: We compute magnetic field due to an infinitely long thin current carrying conductor as shown in Fig. 4.5. Using Ampere's Law, we consider the close path to be a circle of radius as shown in the Fig. 4.5.  
 
If we consider a small current element , is perpendicular to the plane containing both and . Therefore only component of that will be present is ,i.e., .

By applying Ampere's law we can write,

                                                 ......................................(4.11)   

Therefore,    which is same as equation (4.7)