AFMC AFMC Solved Paper-2000

  • question_answer
    A cyclotron is operating at a frequency of \[12\times {{10}^{6}}Hz.\]Mass of deuteron is \[3.3\times {{10}^{27}}kg\]and charge on deuteron is \[1.6\times 10'19\text{ }C.\] To accelerate deuterons the magnetic induction of the necessary magnetic field is :

    A)  0.016 T                                

    B)  0.16 T

    C)  16 T                                      

    D)  1.6T

    Correct Answer: D

    Solution :

                     A cyclotron accelerates charged particles with a   high-frequency,   alternating   voltage (potential   difference).   A   perpendicular magnetic field causes the particles to go almost in a circle. Also a high frequency alternating voltage applied across the 'D1 electrodes alternately attracts and repels charged particles. The centripetal force is provided by the transverse magnetic field B, and the force on a particle travelling in a magnetic field (which causes it to curve) is equal to BqV. So,        \[\frac{m{{v}^{2}}}{r}=Bqv\]where, m is mass, q is charge, v is velocity and r is radius. Also         \[v=r\omega \] \[\therefore \]                   \[\omega =\frac{Bq}{m}\] Since,      \[\omega =2\pi n,\]we have                   \[2\pi n=\frac{Bq}{m}\] \[\Rightarrow \]                           \[B=\frac{2\pi n\times m}{q}\]              \[=\frac{2\times \pi \times 12\times {{10}^{6}}\times 3.3\times {{10}^{-27}}}{1.6\times {{10}^{-19}}}\] \[\approx 1.6\,\text{T}\]


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