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InterviewSolution
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A particle of mass `m` having negative charge `-q` is projected at an angle `theta` with `x`-axis. There exists uniform electric field `E` and a unifrom magnetic field `B` along `x`-axis. The particle will return to its intial point once if (`n` is some integer) A. `n=(Bvcostheta)/(piE)`B. `n=(2Bvcostheta)/(piE)`C. `n=(Bvsintheta)/(piE)`D. `n=(2Bvsintheta)/(piE)` |
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Answer» Correct Answer - A Let particle completes `n` revolutions in time `t`, then `t=nT` `implies t=(n2pim)/(qB)` If particle has to return to its initial point, the displacement along `x`-axis during this time should be zero. `s_(x)=u_(x)t+(1)/(2)a_(x)t^(2)` ` implies 0=vcosthetat-(1)/(2)(qE)/(m)t^(2)` ` impliesvcostheta=(qE)/(2m)t` ` impliesvcostheta=(qE)/(2m)(n2pim)/(qB)impliesn=(Bvcostheta)/(piE)` |
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