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A proton, an electron, and a helium nucleus, have the same energy. They are in circular orbits in a plane due to magnetic field perpendicular to the plane. Let r p , r e and r He be their respective radii, then,

1. r e < r p < r He
2. r e > r p = r He
3. r e < r p = r He
4. r e > r p > r He

Correct answer: r e < r p = r He

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