The diagram below shows the top view of the Wire A shown by a cross (X), carrying current into the plane of the paper. Which of the compasses is correctly aligned with the magnetic field produced by the current carrying wire?
- (a)Only 1 is aligned
- (b)Only 2 is aligned
- (c)Both 1 and 2 are aligned
- (d)Both 1 and 2 are not aligned
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Only 1 is aligned
Reason — A straight current-carrying wire produces circular magnetic field lines around it so using the right-hand thumb rule, if the current is into the plane of the paper (shown by X), the magnetic field lines circulate clockwise.
A compass needle aligns tangentially to these field lines and at the position of compass 1, the field direction is towards the right, so compass 1 is correctly aligned.
At the position of compass 2, the magnetic field should point downward, but the compass is shown pointing upward, so it is not correctly aligned.
Therefore, only compass 1 is aligned correctly.