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BITSAT 2015
Exam
BITSAT
Year
2015
Subject
Physics
Chapter
Magnetic Effects of Current

BITSAT 2015 · Physics · Magnetic Effects of Current

Two particles X and Y having equal charges, after being accelerated...

Two particles X\mathrm{X} and Y\mathrm{Y} having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii R1\mathrm{R}_{1} and R2\mathrm{R}_{2}, respectively. The ratio of masses of X\mathrm{X} and Y\mathrm{Y} is

Options

  1. A(R1/R2)1/2\left(\mathrm{R}_{1} / \mathrm{R}_{2}\right)^{1 / 2}
  2. B(R2/R1)\left(\mathrm{R}_{2} / \mathrm{R}_{1}\right)
  3. C(R1/R2)2\left(\mathrm{R}_{1} / \mathrm{R}_{2}\right)^{2}
  4. D(R1/R2)\left(\mathrm{R}_{1} / \mathrm{R}_{2}\right)

Correct answer

C. (R1/R2)2\left(\mathrm{R}_{1} / \mathrm{R}_{2}\right)^{2}

Step-by-step solution

When a charge particle is allowed to move in a uniform magnetic field, then it describes spiral or circular path \begin{array}{l} \text{ Centripetal force, } \frac{\mathrm{mv}^{2}}{\mathrm{R}}=\mathrm{qvB} \quad \therefore \\ \mathrm{v}=\left(\frac{\mathrm{qB}}{\mathrm{m}} \mathrm{R}\right) \\ \text{ Hence, } \sqrt{\frac{2 \mathrm{q} \mathrm{V}}{\mathrm{m}}}=\left(\frac{\mathrm{qB}}{\mathrm{m}}\right) \mathrm{R}\left[\because \mathrm{V}=\sqrt{\frac{2 \mathrm{qV}}{\mathrm{m}}}\right] \\ \Rightarrow \mathrm{R}=\left(\frac{2 \mathrm{mV}}{\mathrm{q}}\right)^{1 / 2} \times \frac{1}{\mathrm{~B}} \\ \text{ or, } \mathrm{m} \propto \mathrm{R}^{2} \end{array} [∵V,q[\because \mathrm{V}, \mathrm{q} and B\mathrm{B} are constant ]]  or, m1 m2=(R1R2)2\text{ or, } \frac{\mathrm{m}_{1}}{\mathrm{~m}_{2}}=\left(\frac{\mathrm{R}_{1}}{\mathrm{R}_{2}}\right)^{2}
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