Question

(a) Under what conditions is the phenomenon of total internal reflection between the critical angle of incidence and the refractive index of the medium.
(b) Three lenses of focal lengths+10 cm, -10 cm and + 30 cm are arranged coaxially as in the figure given below. Find the position of the final image formed by the combination.

Answer 1

`"For Lens "L_(1)`
`1/f=1/v-1/u,`
`1/v=(30-10)/300=20/300=1/15`
`For Lens"L_(2)`
`u=(+15-5)=10cm,`
`1/v=0,`
`"For Lens"L_(3)`
`u=oo`
`f=+30cm,`
`1/v=1/30,`
Final Image will be +30 cm from `L_(3)`.
`u=-30xm`
`110=1/v-1/(-30),`
`v=15 cm`
`f=-10cm,`
`v=oo`
`1/f=1/v-1/u,`
`v=+30 cm`
f=+10cm
`1/10-1/30-1/v`
1/f=1/v-1/10`
`1/(+30)=1/v-1/oo`