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A proton and an α -particle (with their masses in the ratio of 1 : 4 and charges in the ratio of 1 : 2) are accelerated from rest through a potential difference V. If a uniform magnetic field (B) is set up perpendicular to their velocities, the ratio of the radii r p : r α of the circular paths described by them will be ;

1. 1 : 3
2. 1 : 3
3. 1 : 2
4. 1 : 2

Correct answer: 1 : 2

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