Shows a convex lens of focal length 12 cm lying in a uniform magnetic field B of magnitude 1.2 T parallel to its principal axis. A particle having a charge `2.0X 10^(-3) C` and mass `2.0 X 10^(-5)` kg is projected perpendiucular to the plane of the diagram with a speed of `4.8 ms ^(-1).` The particle moves along a circle with its centre on the principal axis at a distance of 18 cm from the lens. Show that the image of the particle goes along a circle end find the radius of thet circle.

Explanation

The object will make a path , perpndicular to the plane of paper
Let the radius 0f the object be ,brgt Then `r = (mq)/(qB)`
Here object distance `= k = 18 cm`
Using (lens equation ), `v = 36 cm`.
Let the circular path of image `= r'
So, magnification `= (magnetic path )
Thus `r' = 2 xx 4 = 8 cm`.
Hence the radius of the circular path in
which the image move is 8 cm.