Question

A plane convex lens of focal length and radius with refractive index n derive its lens makes formula ​

Answer 1

Answer: Figure shows a plano-convex lens of refractive index μ=n.

From Lens Maker's formula:-

f

1

​

=(  

μ  

1

​

 

μ  

2

​

 

​

−1)(  

R  

1

​

 

1

​

−  

R  

2

​

 

1

​

)

                  where, μ  

2

​

 and μ  

1

​

 are refractive index of lens and surrounding medium respectively.

                   And,  R  

1

​

  and R  

2

​

 are radius of 1st and 2nd surfaces respectively.

Here,  

 μ  

1

​

=1,μ  

2

​

=n,R  

1

​

=−∞,R  

2

​

=−R,f=2R

Hence,

   

f

1

​

=(n−1)(  

−∞

1

​

−  

−R

1

​

)

 

 ⟹  

f

1

​

=(n−1)  

R

1

​

 

⟹f=  

n−1

R

​

Answer 2

Answer:

f=R/2 is the correct answer