A positive charge is moving towards an observer. The direction of magnetic induction lines is

Options

A. Anticlockwise, if charge is positive
B. Anticlockwise, if charge in negative
C. Clockwise, if charge is positive
D. Clockwise, if charge is negative

Answer

a, d

Explanation

The direction of the motion of positive charge is treated as the direction of current and it is opposite to it for negative charge. To understand the flow of circular magnetic lines around straight wire, the right hand thumb rule is most convenient. If you align the right hand thurnb in the direction of current, then the sense in which we can curl the fingers of same hand represents the sense of magnetic line around it.
Magnetic line will be observed anticlockwise if charge is positive and clock wise if charge is negative. Hence options (a) and (d) are correct.