Question

While evaluating magnetic field due to an infinitesimal current element at a point, the direction of field in accordance with cross-product rule will be?

• A. Perpendicular to infinitesimal length vector
• B. Perpendicular to position vector of the point
• C. Perpendicular to both length and position vector
• D. Parallel to both length and position vector

Answer 1

The correct option is C Perpendicular to both length and position vector

If C=AxB, then C will be perpendicular to both A and B, or in other words you can say that it will be perpendicular to the plane containing A and B. Thus magnetic field is perpendicular to the plane containing dl and r.
dl=elementary length vector
r=position vector of the point at which field has to be calculated