**Problem : **

A wire carrying a current ** I** runs from the origin to the point

What is the magnetic field strength at point *P*?

Recall that when we derived the field of an infinite straight wire we evaluated an integral from negative infinity to infinity. We are still dealing with a straight wire here; we must simply change our limits of integration. Recall that:

B | = | ||

= | - | ||

= | - |

This answer is complicated, but is a general answer for this kind of situation.

**Problem : **

What is the magnitude and direction of the magnetic field at the center of a
square wire with sides of length *d* and current ** I**?

We begin by drawing a diagram:

A square wire, with distances shown.

B | = | ||

= | + | ||

= | |||

= | = |

Recall that this is only for one segment. Thus the total magnetic field at the center of the square is:

Take a Study Break!