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JEE Main 2025 (7 Apr, Shift 1) · Moving Charge in a Magnetic Field

Moving Charge in a Magnetic Field question from JEE Main 2025 (7 Apr, Shift 1)

Q19JEE Main 2025 · 7 APR · SHIFT 1Medium

Moving Charge in a Magnetic Field

A particle of charge $q$ , mass $m$ and kinetic energy $E$ enters in magnetic field perpendicular to its velocity and undergoes a circular arc of radius (r). Which of the following curves represents the variation of $r$ with $E$ ?

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Answer: (a)

$r = \dfrac{mv}{qB} = \dfrac{\sqrt{2mE}}{qB} \Rightarrow r \propto \sqrt{E}$
The graph of $r$ against $E$ starts at the origin and rises with decreasing slope (a sideways parabola $r^2 \propto E$ ).
So the answer is (a).

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