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In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular path of radius R using a magnetic field B. If V and B are kept constant, the ratio (charge on the ion / mass of the ion) will be proportional to
- 1/R²
- R²
- R
- 1/R
Correct answer: 1/R
Solution
The radius R of the semicircular path in a mass spectrometer is given by the equation R = (mv)/(qB), where m is the mass, v is the velocity, q is the charge, and B is the magnetic field. Using the energy relation qV = (1/2)mv², we find that q/m is proportional to 1/R. Hence, the correct answer is D.
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