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QPages 228-229: Q4: HC Verma: Concepts of Physics - Volume 2 Magnetic Field Pages 228-229: Q4 Solution: The free electrons in a conducting wire are in constant thermal …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often incorrectly assume that because individual electrons experience a magnetic force ($F = qv \times B$) due to thermal motion, the wire must also experience a net force. You must recognize that while individual forces exist, their random directions cause the vector sum to average to zero, resulting in no net force on the wire.

The free electrons in a conducting wire are in constant thermal motion. If such a wire, carrying no current, is placed in a magnetic field, is there a magnetic force on each free electron? Is there a magnetic force on the wire?

Step-by-Step Verified Solution

**Answer:** Yes, there is a magnetic force on each free electron. No, there is no net magnetic force on the wire. **Step-by-Step Explanation:** Even in a wire carrying no current, free electrons have random thermal motion. Each electron moving with velocity v⃗\vec{v} experiences a force F⃗=qv⃗×B⃗\vec{F} = q\vec{v} \times \vec{B}. However, these forces are random in direction and average out to zero over time. The wire as a whole experiences no net force because the net current is zero.

All Questions in this Chapter

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