Question

A vertical wire carries a current upward. The magnetic field north of the wire will be directed:
A. Upward
B. Eastward
C. Westward
D. Northward

Answer 1

To get the direction of the magnetic field lines the Right-Hand Thumb Rule can be used. Right-hand Thumb rule states that, if the thumb of the right hand is in the direction of the current flow then, the curl fingers show the direction of the magnetic field.

Complete step by step answer:
To find the direction of the magnetic field due to a current-carrying element Right Hand Thumb Rule is used. The Right-Hand Thumb Rule goes as follows, Right-hand Thumb rule states that, if the thumb of the right hand is in the direction of the current flow then, the curl fingers show the direction of the magnetic field.
Now coming to the question at hand. It is given that the current is flowing a straight wire and the direction of the current is given to be upward. So we place the Right hand with the thumb facing upward.

In the figure, I represents the direction of current and B represents the direction of the magnetic field. As can be clearly seen from the figure that the direction of the magnetic field lines north of the wire, when current is flowing upward, is westward.
So, Option C is the correct one.

Note:
The magnetic field lines produced by a current-carrying straight wire have circular symmetry. The lines of magnetic force are concentric circles with the wire passing through the common centre of the circles. The plane of the magnetic field is normal to the length of the straight current-carrying wire.