KVPY Sample Paper KVPY Stream-SX Model Paper-22

  • question_answer
    A charged particle (of charge q and mass m) is projected between plates of a parallel plate capacitor as shown at\[t=0\]. Time t at which instantaneous power delivered by the electric field to the particle is zero is

    A) \[\frac{2mu{{\varepsilon }_{0}}\sin \alpha }{q\sigma }\]

    B) \[\frac{mu{{\varepsilon }_{0}}\sin \alpha }{q\sigma }\]

    C) \[\frac{mu{{\varepsilon }_{0}}\sin \alpha }{2q\sigma }\]  

    D) \[\frac{mu{{\varepsilon }_{0}}\sin \alpha }{4q\sigma }\]

    Correct Answer: B

    Solution :

    \[{{u}_{y}}=u\sin \alpha ,{{a}_{y}}=\frac{Eq}{m}=\frac{\sigma q}{{{\varepsilon }_{0}}m}\]
    Using \[{{v}_{y}}={{u}_{y}}-at,\]we have
    \[0=u\sin \alpha -\frac{\sigma q}{{{\varepsilon }_{0}}m}t\Rightarrow t=\left( \frac{mu{{\varepsilon }_{0}}\sin \alpha }{q\sigma } \right)\]

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