InterviewSolution
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InterviewSolution
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A particle of charge `+q` and mass `m` moving under the influence of as uniform electric field `Ehati` and uniform magnetic field `B hatk` follows trajectory form `P` to `Q` as shown in figure. The velocities at P and Q re `vhati and -2hatj`. Which of the following statement(s) is/are correct? `a. E=3/4[(mv^2)/(qa)]` b. Rate of work done by the electrif field at P is `3/4[(mv^3)/a]` c. Rate of work done by the electric field at `P` is zero. d. Rate of work done by both the field at `Q` is zero.A. (i), (ii)B. (ii), (iv)C. (i), (ii), (iv)D. (i), (iv) |
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Answer» Correct Answer - C (i) Work is done only by electric force. By work-energy theorem between `P` and `Q` `Delta W = K_(2) - K_(1) = K_(Q) - K_(P)` `qE xx 2a = (1)/(2)m(2v^(2)) - (1)/(2)mv^(2) = (3)/(2)mv^(2)` `E = (3mv^(2))/(4qa)`, (i) is O.K. (ii) `P = vec(F)_(e). vec(v) = qvec(E).vec(v) = q(Ehat(i)).(v hat(i)) = qEv` (iv) Work done by magnetic force is always force is always zero At `Q`, `F_(e)_|_^(ar)v, P = 0` (iv) is O. K. |
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