# Magnetic Field due to a Straight Wire

Magnetic field due to a current carrying wire at point

*P*which lies at perpendicular distance*r*from the wire, as shown in Fig. 15, is given as:From Fig. 15

**Fig. 15**

and

Hence,

# For a wire of finite length

The magnetic field at a point which lies on perpendicular bisector of the finite length wire,

*φ*

_{1}=

*φ*

_{2}=

*φ*ﬁ So

**Fig. 16**

# For a wire of infinite length

When the linear conductor

*XY*is of infinite length and point*P*lies near the center of the conductor,*φ*_{1}=*φ*_{2}= 90^{o}.**Fig. 17**

# For a wire of semi-infinite length

When the linear conductor is of infinite length and point

*P*lies near the end*Y*or*X*,*φ*_{1}= 90° and*φ*_{2}= 0°.So,

**Fig. 18**

# For axial position of wire

When point

*P*lies on the axial position of the current-carrying conductor, then magnetic field at*P*is given as:*B*= 0**Fig. 19**