Question

A loop of flexible wire of irregular shape carrying current is placed in an external magnetic field. Identify the effect of the field on the wire.

• A. shape of the loop remains unchanged
• B. loop assumes circular shape with its plane normal to the field
• C. loop assumes circular shape with its plane parallel to the field
• D. wire gets stretched to become straight

Hint:

Magnetic systems always work towards the state of minimum potential energy, which corresponds to maximum magnetic flux.

Answer 1

The Correct Option is B

This question assesses the understanding of the interaction between a current-carrying wire and an external magnetic field. Let's analyze the problem carefully.

1. The wire is carrying a current and is placed in a magnetic field. According to Ampère's force law, a current-carrying wire experiences a force when placed in a magnetic field.
2. This force can be understood using the concept of magnetic tension, which tends to minimize the potential energy by adjusting the shape of the wire.
3. This effect can be described using the Lorentz force law, which states that a moving charge in a magnetic field experiences a force perpendicular to both the direction of magnetic field and direction of current. For a complete loop, the forces on opposite sides typically cancel out, but they have a net effect on the loop’s shape.
4. Due to magnetic tension, the loop will try to minimize its energy, adopting a shape of least resistance or least energy consumption, which is usually a circle.
5. The loop will tend to rearrange itself such that its plane is perpendicular to the direction of the magnetic field. This is because in such an orientation, the magnetic flux through the loop is maximized, further minimizing the system's energy.

Conclusion: The correct answer is that the "loop assumes a circular shape with its plane normal to the field". This is because the tendency of the loop is to adjust in such a way that the magnetic forces lead to a minimum energy configuration, which is circular and aligned perpendicular to the magnetic field direction.

Let's rule out the other options:

• "shape of the loop remains unchanged" : This is incorrect because the wire does not remain in an irregular shape when external forces are acted upon it.
• "loop assumes circular shape with its plane parallel to the field" : This is incorrect because the magnetic forces would induce tension in the wire to rearrange itself perpendicular to the field.
• "wire gets stretched to become straight" : This is incorrect because the interaction of the magnetic field will promote a closed loop shape instead of a straight wire.

This understanding of basic electromagnetic principles can be critical for various practical applications and understanding the fundamentals of electromagnetism in physics.