Question

The diagram below shows the top view of the Wire A shown by a cross (X) carrying current into the plane of the paper. Which of the compasses is correctly aligned with the magnetic field, produced by the current carrying wire?

• A. Only 1 is aligned
• B. Only 2 is aligned
• C. Both 1 and 2 are aligned
• D. Both 1 and 2 are not aligned

Hint:

Remember the conventions for current direction: \(\otimes\) (cross) is current going INto the page (like the tail of an arrow), and \(\odot\) (dot) is current coming OUt of the page (like the tip of an arrow).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify which compass needle correctly shows the direction of the magnetic field around a straight wire carrying current into the page.
Step 2: Key Formula or Approach:
We use the Right-Hand Thumb Rule to determine the direction of the magnetic field lines around a current-carrying conductor.
Rule: If you point the thumb of your right hand in the direction of the current, the direction in which your fingers curl gives the direction of the magnetic field lines.
Step 3: Detailed Explanation:
1. The symbol \(\otimes\) (a cross) represents a current flowing into the plane of the paper.
2. Applying the Right-Hand Thumb Rule, point your thumb into the page.
3. Your fingers will curl in the clockwise direction.
4. This means the magnetic field lines are concentric circles around the wire, directed clockwise.
5. A compass needle always aligns itself tangentially to the magnetic field line at its location, with the north pole (arrowhead) pointing in the direction of the field.
Analysis of Compass 1:
- At the position of compass 1 (top of the circle), the tangent to the clockwise circle points to the right. The image seems to show compass 1 is on the left of the wire. At this position, the tangent to the clockwise circle points downwards. The compass needle 1 is shown pointing downwards. Thus, compass 1 is correctly aligned.
Analysis of Compass 2:
- At the position of compass 2 (bottom of the circle), the tangent to the clockwise circle points to the left. The compass needle 2 is shown pointing upwards. This is incorrect.
Step 4: Final Answer:
Based on the Right-Hand Thumb Rule, the magnetic field is clockwise. Only compass 1 is correctly aligned with the clockwise magnetic field direction at its location.