Hans Christian Oersted → discovered electricity and magnetism are linked.
- source of magnetism is moving electric charges → which in turn produces electricity
In Experiment → Oersted found that wire carrying current ⇒ caused a compass needle to deflect → indicating presence of magnetic field.
Positions of the needles of the compass → indicate the direction of magnetic field generated by the current passing through a straight conductor.
if the card in (b) in image → is raised/lowered to a new position → directions of needles do not change
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this suggests that magnetic field produced by a current carrying conductor forms a cylinder around the conductor
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If the compasses on the card → are repositioned further from the conductors → the needles of the compass again form a circle → around the conductor as before.
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If the card is moved up and down → needles remain in their deflected position. This suggests that the magnetic field produced forms concentric cylinders around the conductors
If direction of current is reversed → the needles deflect in the opposite direction
- moving the card up and down along entire conductor → shows the same deflection of needles.
- Compasses are then removed → iron fillings are sprinkled evenly over entire card.
- current flowing in the conductor is slowly increased.
- iron fillings initially form fewer concentric circles around conductor.
- as current is increased further, more concentric circles are formed.
directions of the needles on the compass follow the right hand grip rule
- if we grip conductors with thumb pointing in direction of conventional current → the curl of the fingers shows the direction of the magnetic field.
Conclusion
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changing the magnitude of the current changes the strength of the magnetic field. the strength of the magnetic field increases when the current is increased.
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changing direction of the current changes the direction of the magnetic field. direction of magnetic field is reversed when the direction of current is reversed. this direction is given by the hand grip rule.
in the 2 images → the magnetic field lines near the wire → are closer together than the ones further away from the wire.
- this is because the strength of the magnetic field is stronger closer to the wire.
This field is produced by current → is temporary.
- as soon as current stops flowing → magnetic field disappears.
- hence it is possible to use this property to make temporary magnets such as in a solenoid.
Important
Method to determine poles of magnet.
- looking into the solenoid.
- if the current flows clockwise it is south pole and if current flows anticlockwise it is north pole.