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⚛️ Physics  ·  Moving Charges and Magnetism  ·  NEET & JEE

A proton and a deuteron (mass twice the proton) enter a magnetic field perpendicularly with the same momentum. The ratio of their circular radii r<sub>p</sub> : r<sub>d</sub> is:

Answer: 1 : 1.

  • A 1 : 1
  • B 1 : 2
  • C 2 : 1
  • D 1 : &radic;2

Correct answer: A. 1 : 1

Explanation: r = p/(qB). Both have the same momentum p and the same charge q in the same field B, so the radii are equal, 1 : 1.

Magnetic Field Lines Around a Straight WireIfield forms concentric circles around the wire (right-hand rule)

The magnetic field around a long straight current-carrying wire forms concentric circles, with direction given by the right-hand rule (point thumb along I, fingers curl in the direction of B).

Concept context

Magnetic force on moving charges and currents, the Biot-Savart law, Ampere's law, and the cyclotron - how electric currents create and respond to magnetic fields.

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