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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2005

  • question_answer
    Electron of mass m and charge q is travelling with a speed v along a circular path of radius r at right angles to a uniform magnetic field of intensity B. If the speed of the electron is doubled and the magnetic field is halved the resulting path would have a radius:

    A)  2 r                                         

    B)  4 r

    C)  r/4                                        

    D)  r/2

    Correct Answer: B

    Solution :

    Radius of path of electron                 \[r=\frac{mv}{Bq}\] m and q remain unchanged. So,          \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{{{\upsilon }_{1}}}{{{\upsilon }_{2}}}\,.\,\,\frac{{{B}_{2}}}{{{B}_{1}}}\]                 \[=\frac{\upsilon }{2\upsilon }\,.\,\frac{B/2}{B}=\frac{1}{4}\Rightarrow \,\,{{r}_{2}}=4r\]


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