Q. An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional to :
A) B/v
B) v/B
C) √(v/B)
D) √(B/v)
Explanation
[Solution from source] The orbiting electron is a current I = ev/(2πr), giving B = μ₀I/(2r) = μ₀ev/(4πr²). So r² ∝ v/B and r ∝ √(v/B). v/B would follow from B ∝ v/r, which ignores that the current itself depends on r. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.