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An electron with kinetic energy K₁ enters between parallel plates of a capacitor at an angle 'α' with the plates. It leaves the plates at an angle 'β' with the plates. Then the ratio of kinetic energies K₁: K₂ will be:

1. sin²β / cos²α
2. cos²β / cos²α
3. cosβ / cosα
4. cosβ / sinα

Correct answer: cos²β / cos²α

Solution

The ratio of kinetic energies K₁ to K₂ is determined by the conservation of energy and the geometry of the electron's motion in the electric field between the plates. The angles α and β relate to the components of the electron's velocity, and the correct option reflects how the kinetic energy changes due to these angles, specifically showing that the kinetic energy is proportional to the square of the cosine of the angles.

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