JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank Motion of Charged Particle In Magnetic Field

  • question_answer
    An electron and a proton enter region of uniform magnetic field in a direction at right angles to the field with the same kinetic energy. They describe circular paths of radius \[{{r}_{e}}\] and \[{{r}_{p}}\] respectively. Then                                        [Manipal MEE 1995]

    A)            \[{{r}_{e}}={{r}_{p}}\]

    B)            \[{{r}_{e}}<{{r}_{p}}\]

    C)            \[{{r}_{e}}>{{r}_{p}}\]

    D)            \[{{r}_{e}}\] may be less than or greater than \[{{r}_{p}}\] depending on the direction of the magnetic field

    Correct Answer: B

    Solution :

                       \[r=\frac{\sqrt{2mK}}{qB}i.e.\ \ r\propto \frac{\sqrt{m}}{q}\] Here kinetic energy K and B are same. \[\therefore \ \frac{{{r}_{e}}}{{{r}_{p}}}=\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\times \frac{{{q}_{p}}}{{{q}_{e}}}\Rightarrow \frac{{{r}_{e}}}{{{r}_{p}}}=\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\ \ (\because \ {{q}_{e}}={{q}_{p}})\]            Since me < mp, therefore re < rp


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