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22.3 Biot- Savart or Laplace's Law
Figure 4
Consider a small element PQ of a conductor through which current i flows. Let d
l be the length of the element. Let A be any point at distance r from the center of the element.
Let the line joining the center 'O' to A make
Ðq with PQ.
Then, the intensity  of the magnetic field at A due to current i in the element PQ is found (by
experiments) to be (in magnitude) proportional to i, d
l, sin q ,  .
The direction of is given by Ampere's rule, which is
perpendicular to the plane in the diagram
and pointing into the plane.
In vector form, equation (1) can be represented as,
Note: Biot- Savart Law is applicable only if the current
is a steady current. This is possible only in closed loops or infinite
conductors.
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