The Earth S Magnetic Field

The radius of the circular path of a charged particle moving in a magnetic field is given by the formula: where:
- is the mass of the particle,
- is the speed of the particle,
- is the charge of the particle,
- is the magnetic field strength.
For a proton, and charge , and for a deuteron, and charge .
Since both particles are moving with the same speed and in the same magnetic field, the ratio of the radii is: Hence, the correct answer is (B) 1 : 2.