Magnetic Effect of an Electric Current Flowing Through a Conductor.
Consider the diagram below of a set up that that can be used to investigate the magnetic effect of an electric current flowing through a conductor. This is commonly called Oersted’s experiment. A and B are magnetic compass needles
When the switch is closed, it is observed that the compass needles deflect towards the directions shown in the diagram below.
- The direction of deflection of the compass needles can be predicted by Ampere’s swimming rule which states that “if one imagines swimming along a conductor in the direction of electric current and facing the compass needle, then the north pole of the needle will be deflected towards the swimmer’s left hand”
Notes:
- The deflection of the compass needles is due to the interaction between the magnetic field due to the electric current in the conductor and the magnetic field of the compass needle.
- When the terminals of the battery are interchanged, the compass needles deflect in the opposite direction because the direction of current reverses.
The extent of deflection of the compass needles increases when the amount of electric current flowing through the conductor increases.
Magnetic Field Patterns on a Straight Current Carrying Conductor
- When a large electric current flows through a wire passing through a card board on which iron filings is sprinkled, the filings form a pattern of concentric circles around the wire as shown below.
- This behavior of iron filings show that the magnetic field around a straight current carrying conductor forms a pattern of concentric circles and is perpendicular to the conductor.
- The direction of this magnetic field pattern can be predicted by Fleming’s right hand grip rule for a current carrying straight conductor which states that “if a current carrying conductor is gripped in the right hand with the thumb pointing along the wire in the direction of current, the other fingers will point in the direction of the magnetic field”.
video on the magnetic effect of an electric curent