Question

Two equal electric currents are flowing perpendicular to each other as shown in figure. Line segments
AB and CD are perpendicular to each other and symmetrically placed with respect to the currents.
Where do we expect the resultant magnetic field to be zero?
(1) On AB
(2) On CD
(3) On both AB and CD
(4) On both OD and OB
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Answer 1

Answer:

The direction of the magnetic field due to a current is given by right hand curled fingers rule.  

Therefore at AB axis, the components of magnetic field will cancel each other and the resultant magnetic field will be zero on AB.

Answer 2

1. The direction of the magnetic field, due to current, is given by the right-hand rule.

2. Right hand rule- The right hand is held with the thumb, index finger and middle finger mutually perpendicular to each other (at right angles).

•The thumb is pointed in the direction of the motion of the conductor relative to the magnetic field.

•The first finger is pointed in the direction of the magnetic field.

•Then the second finger represents the direction of the induced or generated current within the conductor.

3. At axis AB, the components of magnetic field will cancel each other and the resultant magnetic field will be zero.

4. Hence option (1) is correct.