Figure shows a convex lens of focal length `10cm` lying in a uniform magnetic field `B` of magnitude `1.2 T` parallel to its principal axis.A particle havig a charge `2.0xx10^(-3) C` and mass `2.0xx10^(-5) kg` is projected perpendicular to the plane of the diagram with a speed of `4.8 m//s`.The particle moves along a circle with its centre on the principal axis at a distance of `15 cm` from the lens.The axis of the lens and of the circle are same.Show that the image of the particle goes along a circle and find the radius of that circle.

Answer

C

Explanation

`1/V-1/u=1/f rArr1/V+1/15=1/10 rArrV=30cm`
`r_("pacticle")=(mv)/(qB)=(2xx10^(-5)xx4.8)/(2xx10^(-3)xx1.2)=4 cm`
`r_(I)/r_(P)=V/u=2 rArr r_("image")=8cm`