A charged particle enters a uniform magnetic field with a velocity vector at an angle ${45}^0$ with the magnetic field. The pitch of the helical path followed by the particle is p , the radius of the helix will be 

• A

  $\frac{\mathrm{p}}{\sqrt{2}\mathrm{\pi }}$

• B

  $\sqrt{2}\mathrm{p}$

• C

  $\frac{\mathrm{p}}{2\mathrm{\pi }}$

• D

  $\frac{\sqrt{2}\mathrm{p}}{\mathrm{\pi }}$