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When the downward current flows in a straight…north of the wire is

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PHYSICS

When the downward current flows in a straight vertical conductor, the direction of its magnetic field at a point due north of the wire is

  • A. Upward
  • B. North
  • C. South
  • D. West

QUICK ANSWER…

D

DETAILS…

When the downward current flows in a straight vertical

From the sketch above, it is obvious that if the current flows downward as shown by the arrow, according to Maxwell’s right-hand corkscrew rule, the direction of the magnetic field will be clockwise when viewed from the top, and perpendicular to the current direction as shown above.

Now, if we measure the direction of this field with respect to the north, at a point it will be pointing eastward, and at another point it will be pointing westward.

Now for the right answer to the above question:

  1. Option A is incorrect. Upward and north mean the same thing.
  2. Option B is incorrect. north and upward mean the same thing.
  3. C is incorrect. the direction of the magnetic field cannot be same with that of the current.
  4. D is the correct answer.
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KEY-POINTS…

You may please note these/this:

  • For Maxwell’s corkscrew rule, if the direction of current in a conductor is represented by the thumb finger of your right hand, then the direction of the magnetic field lines will be the same direction as those of your curled remaining four fingers. 
  • This implies that if the direction of current were to be upward, the direction of the magnetic field lines will be anticlockwise when viewed from the top.
  • Always view your right-handed corked screw rule from the top not from the bottom.
  • viewing from the bottom will give the wrong result.

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/culled from 2019 JAMB-UTME physics question 21/

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