Magnetic fields (A-level only)

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Question 38
Medium

A mass spectrometer is used to separate isotopes of carbon, as shown in the diagram below.

Mass Spectrometer Diagram

A mixture of 12C+^{12}\text{C}^+12C+ and 14C+^{14}\text{C}^+14C+ ions is first passed through a velocity selector, where a uniform vertical electric field and a uniform magnetic field (pointing into the page) allow only ions of a specific velocity v0 v_0\,v0​ to emerge through the exit slit.

The ions then enter a deflection chamber containing only the uniform magnetic field pointing into the page. They follow semicircular paths and strike a detector plane at a distance D D\,D from the exit slit, where D D\,D represents the diameter of their semicircular path.

If the 12C+^{12}\text{C}^+12C+ ions strike the detector at a distance D12D_{12}D12​ from the exit slit, at what distance D14D_{14}D14​ do the 14C+^{14}\text{C}^+14C+ ions strike the detector?

Assume the mass of 12C+^{12}\text{C}^+12C+ is 12 u12\text{ u}12 u, the mass of 14C+^{14}\text{C}^+14C+ is 14 u14\text{ u}14 u, and both isotopes are singly-ionized with charge +e+e+e.

D14=67D12D_{14} = \frac{6}{7} D_{12}D14​=76​D12​

D14=76D12D_{14} = \frac{7}{6} D_{12}D14​=67​D12​

D14=76D12D_{14} = \sqrt{\frac{7}{6}} D_{12}D14​=67​​D12​

D14=4936D12D_{14} = \frac{49}{36} D_{12}D14​=3649​D12​

Magnetic fields (A-level only) Questions

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