Question bank/NEET UG/Physics

NEET UGPhysicsModerateNEET 2025

A model for quantized motion of an electron in a uniform magnetic field BB states that the flux passing through the orbit of the electron is n(h/e)n(h/e) where nn is an integer, hh is Planck's constant and ee is the magnitude of electron's charge. According to the model, the magnetic moment of an electron in its lowest energy state will be (mm is the mass of the electron)

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Sol. Magnetic force = mv2r\frac{mv^2}{r}

evB=mv2revB = \frac{mv^2}{r}

v=eBrmv = \frac{eBr}{m}

ϕ=BA\phi = BA

nhe=Bπr2\frac{nh}{e} = B\pi r^2

Br2=nheπBr^2 = \frac{nh}{e\pi}

μ=IA\mu = IA

= eTπr2\frac{e}{T}\pi r^2

= e×v2πrπr2\frac{e \times v}{2\pi r}\pi r^2

μ=evr2\mu = \frac{evr}{2}

μ=12e×eBrmr\mu = \frac{1}{2} e \times \frac{eBr}{m} r

μ=12e2Br2m\mu = \frac{1}{2}e^2\frac{Br^2}{m}

μ=12e2nheπm\mu = \frac{1}{2}e^2\frac{nh}{e\pi m}

μ=neh2πm\mu = \frac{neh}{2\pi m}

for n=1n = 1

μ=eh2πm\mu = \frac{eh}{2\pi m}

Source: geekyrakshit/indian-exam-questions / neet2025-code45

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