In the straight wire A, current is flowing in the vertically downwards direction whereas in wire B the current is flowing in the vertically upward direction. What is the direction of magnetic field:(a) in wire A?(b) in wire B?Name the rule which you have used to get the answer.

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According to Maxwell’s right-hand thumb rule, when a current-carrying conductor is held in the right hand so that our thumb points in the direction of the current, and the fingers that have wrapped the conductor gives the direction of the magnetic field lines around the wire.

When thumb points upwards (current flowing vertically upwards), the wrapped fingers are anticlockwise. Hence, the direction of the magnetic field is anticlockwise.

While when thumb points downwards (current flowing vertically downwards), the wrapped fingers are clockwise. Hence, the direction of the magnetic field is clockwise.