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If an electron and a proton having same momenta enter perpendicular to a magnetic field, then
Asked in JEE Main 2002 · Circular motion: radius, period and energy
- (1) curved path of electron and proton will be same (ignoring the sense of revolution)
- (2) they will move undeflected
- (3) curved path of electron is more curved than that of the proton
- (4) path of proton is more curved.
Answer: (1) curved path of electron and proton will be same (ignoring the sense of revolution)
Step-by-step solution
r = p/(qB).
Same p and same magnitude of charge e, so equal radii.
Paths are equally curved (opposite senses).
Why the other options are wrong
- (2) Forgets that a perpendicular field always deflects a moving charge.
- (3) Assumes the lighter particle bends more, which holds for equal speed, not equal momentum.
- (4) Assumes the heavier particle bends more.
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