Question:medium

A charged particle is moving in a uniform magnetic field \( \vec{B} \) with a constant speed \( v \) in a circular path of radius \( r \). Which of the following graphs represents the variation of radius of the circle, with the magnitude of magnetic field \( \vec{B} \)?

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Remember, for a charged particle moving in a magnetic field, the radius of the circular path is inversely proportional to the magnetic field strength.
Updated On: Feb 22, 2026
  • A
  • B
  • C
  • D
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The Correct Option is B

Solution and Explanation

To solve this problem, we need to analyze the relation between the radius of the circular path of a charged particle and the magnitude of the magnetic field in which it is moving.

The radius \( r \) of the circular path is given by the formula:

\(r = \frac{mv}{qB}\)

where:

  • \(m\) is the mass of the particle,
  • \(v\) is the speed of the particle,
  • \(q\) is the charge of the particle,
  • \(B\) is the magnitude of the magnetic field.

From the formula, it's clear that the radius \( r \) is inversely proportional to the magnetic field \( B \). Thus, as \( B \) increases, the radius \( r \) decreases following an inverse relationship.

The graph that represents an inverse relationship between \( r \) and \( B \) is a hyperbola. Among the given options, the graph in option B represents this inverse relationship:

Therefore, the correct answer is Option B.

This graph correctly shows that as the magnetic field strength increases, the radius of the path decreases, confirming the inverse proportionality.

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