Question

find the maximum and minimum focal length of eye lens
explain breifly
​

Answer 1

The maximum focal length of eye lens is 2.5 cm.

The minimum focal length of eye lens is 2.27 cm.

• Relation between u, v, f is given by

               $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$  ---------------------------(1)

       where,

               u = object distance

               v = image distance

                f = focal length

• The distance between lens and retina is 2.5cm.
• Image is formed at retina.
• Hence, image distance for eye lens(v) = 2.5cm
• Maximum focal length:
• For maximum focal length, object is at infinity.
• Hence, in this case u = - ∞, v = 2.5 cm, $f_{max}$ = ?
• Substituting above values in (1)

                 $\frac{1}{2.5} - \frac{1}{-infinity} = \frac{1}{f_{max} }$

                 $\frac{1}{2.5} + 0 = \frac{1}{f_{max} }$

                 $f_{max}$ = 2.5 cm

• Minimum focal length:
• For minimum focal length, object distance is 25 cm(least distance of distinct vision).
• Hence, in this case u = 25, v = 2.5 cm, $f_{min$ = ?
• Substituting above values in (1)

                 $\frac{1}{2.5} - \frac{1}{-25} = \frac{1}{f_{min} }$

                 $\frac{1}{2.5} + \frac{1}{25} = \frac{1}{f_{min} }$

                  $\frac{11}{25} = \frac{1}{f_{min} }$

                  $f_{min$ = 25/11

                 $f_{min$ = 2.27 cm

Answer 2

Answer:

he maximum focal length of eye lens is 2.5 cm.

The minimum focal length of eye lens is 2.27 cm.

Relation between u, v, f is given by

                ---------------------------(1)

      where,

              u = object distance

              v = image distance

               f = focal length

The distance between lens and retina is 2.5cm.

Image is formed at retina.

Hence, image distance for eye lens(v) = 2.5cm

Maximum focal length:

For maximum focal length, object is at infinity.

Hence, in this case u = - ∞, v = 2.5 cm,  = ?

Substituting above values in (1)

                 

                 

                 = 2.5 cm

Minimum focal length:

For minimum focal length, object distance is 25 cm(least distance of distinct vision).

Hence, in this case u = 25, v = 2.5 cm,  = ?

Substituting above values in (1)

                 

                 

                 

                  = 25/11

                 = 2.27 cm

Step-by-step explanation: