JEE Main Physics Class 12 Ray Optics and Optical Instruments Part 1 Questions

According to question, final image i.e., v2=25cm,
f0=1cm, magnification, m=m1m2=100
Using lens formula,For first lens or objective =

1

v1

−

1

−x

=

1

1

⇒v1=

x

x−1

Also magnification |m1|=|

v1

u1

|=

1

x−1

For 2 nd lens or eye-piece, this is acting as object
∴u2=−(20−v1)=−(20−

x

x−1

) and v2=−25cm
Angular magnification |mA|=|

D

u2

|=

25

|u2|

Total magnification m=m1mA=100
(

1

x−1

)(

25

20− x x−1

)=100
⇒

25

20(x−1)−x

=100 ⇒1=80(x−1)−4x
⇒76x=81⇒x=

81

76

⇒u2=−(20−

81 76

81 76 −1

) =

−19

5

Again using lens formula for eye-piece

1

−25

−

1

− 19 5

=

1

fe

⇒fe=

25×19

106

≈4.48cm