RAJASTHAN PMT Rajasthan - PMT Solved Paper-2009

  • question_answer
    A proton, a deuteron and an a-particle having the same momentum, enters a region of uniform electric field between the parallel plates of a capacitor. If the electric field is perpendicular to the initial direction of the particles. Then, the ratio of deviations of these particles

    A)  1 : 2 : 8                                

    B)  1 : 2 : 4

    C)  1 : 2 : 2                

    D)         1 : 1 : 2

    Correct Answer: A

    Solution :

    Force acting on charge particle in normal direction of motion.                                 \[F=Eq\] Acceleration       \[a=\frac{F}{m}=\frac{Eq}{m}\] If particle travels a distance \[d\] in time\[t\], then                                 \[t=\frac{d}{v}\] Motion in normal direction                                 \[y=\frac{1}{2}a{{t}^{2}}\]                                 \[y=\frac{1}{2}\times \frac{Eq}{m}\times \frac{{{d}^{2}}}{{{v}^{2}}}\] But                         \[p=mv\] \[\therefore \]                  \[y=\frac{Eq{{d}^{2}}\cdot m}{2{{p}^{2}}}\] \[\therefore \]                  \[y\propto \frac{qm}{{{p}^{2}}}\] \[\therefore \]  \[{{y}_{p}}:{{y}_{d}}:{{y}_{\alpha }}=\frac{{{q}_{p}}{{m}_{p}}}{p_{p}^{2}}=\frac{{{q}_{d}}{{m}_{d}}}{p_{d}^{2}}=\frac{{{q}_{\alpha }}{{m}_{\alpha }}}{p_{\alpha }^{2}}\] Given,   \[{{p}_{p}}={{p}_{d}}={{p}_{\alpha }}\]                 \[{{q}_{p}}=e,\]                \[{{q}_{d}}=e,\]                \[{{q}_{\alpha }}=2e\]                 \[{{m}_{p}}=m,\]   \[{{m}_{d}}=2m,\]    \[{{m}_{\alpha }}=4m\] \[\therefore \]  \[{{y}_{p}}:{{y}_{d}}:{{y}_{\alpha }}=e\times m:e\times 2m:2e\times 4m\]                 \[=1:2:8\]


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