Question

A person is standing facing geographic north and a vertical wire in front of him is carrying a current in downward direction. The direction of magnetic field at a point on the right side of wire is:

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

Hint:

Use the right-hand thumb rule with the thumb along the downward current. The point on the right of a person facing north is east of the wire.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
We need the direction of the magnetic field near a long vertical wire that carries current downward. The point is to the right of the wire, as seen by a person facing north.

Step 2: Key Approach:
Use the right-hand thumb rule. Point the thumb of the right hand along the current. The curled fingers show how the magnetic field lines circle the wire.

Step 3: Set up the directions:
Facing north, the person's right hand is towards the east. So the point lies to the east of the wire. Let up be the vertical direction. The current flows down.

Step 4: Apply the thumb rule:
With the thumb pointing down, the fingers curl clockwise when seen from above. A clockwise circle seen from above goes east to south to west to north.
At the point east of the wire, the field is tangent to the circle, and clockwise motion at the east point goes towards the south. So the field there points south.

Step 5: Check the other options:
East is along the line joining the wire and the point, but the field is always perpendicular to this line, so (B) is wrong.
West is also along that line, so (C) is wrong.
North would be the field if the current were upward, so (D) is wrong.

Final Answer:
The field at the point on the right of the wire points towards the south. This is option (A). \[ \boxed{\text{South}} \]