# focal length of eye lens of a healthy man is about

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## The focal length of a normal eye

Click here👆to get an answer to your question ✍️ The focal length of a normal eye - lens is about:

Question

## The focal length of a normal eye-lens is about:

**A**

## 1 mm

**B**

## 2 cm

**C**

## 25 cm

**D**

## 1 m

Easy Open in App

Updated on : 2022-09-05

Solution Verified by Toppr

Correct option is B)

## The focal length of a normal eye lens is about 2 cm because distance between eye lens and retina is approximately 2 cm. So, when parallel rays are coming they form image at focus and to make image at retina focal length should be about 2 cm.

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## The focal length of a normal eye lens is about

Normal diameter of human eye is 2.5 cm. When the eye is focussed on a distant object, the ciliary muscules are relaxed so that the focal length of the eye has its maximum value equal to the diameter of the eye. When the eye is focussed on a closer object, ciliary muscles are strained and the focal length of the eyelens decreases.

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The focal length of a normal e...

The focal length of a normal eye lens is about

Updated On: 27-06-2022

<2.5<2.5( 00 : 22 ) ADVERTISEMENT Text Solution Open Answer in App A equal to 2.5 2.5 B >2.5 >2.5 C D Both (a) and (c ). Answer

The correct Answer is D

Solution

Normal diameter of human eye is

2.5 2.5

cm. When the eye is focussed on a distant object, the ciliary muscules are relaxed so that the focal length of the eye has its maximum value equal to the diameter of the eye. When the eye is focussed on a closer object, ciliary muscles are strained and the focal length of the eyelens decreases.

Answer

Step by step solution by experts to help you in doubt clearance & scoring excellent marks in exams.

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## The focal length of a normal eye

The focal length of a normal eye-lens is about:$(a){\\text{ 1mm}} \\\\(b){\\text{ 2cm}} \\\\(c){\\text{ 25cm}} \\\\(d){\\text{ 1m}} \\\\ $. Ans: Hint: In this question use the concept that focal length is nothing but the distance between the ...

The focal length of a normal eye-lens is about:(a) 1mm (b) 2cm (c) 25cm (d) 1m

(a) 1mm(b) 2cm(c) 25cm(d) 1m

Answer Verified 268.5k+ views

Hint: In this question use the concept that focal length is nothing but the distance between the eye lens of human beings and the retina present inside the eyes. This will help get the right default value of focal length of the human eye.

Complete Step-by-Step solution:

Consider an eye lens as shown in the figure and the retina of the eye acts as a screen on which the real image is formed.

So the focal length is the distance between the eye lens and the retina.

So when as a source of light coming from the infinity it passes through the eye lens and converges it on the retina as shown in the figure.

So for a normal eye lens the focal length is about 2 cm or 20 mm (when eye is in relaxed position).

So this is the required answer.

Hence option (B) is the correct answer.

Note – For a normal eye, when the eye muscles are relaxed, the focal length f of the lens L is slightly less than its diameter, which is D = 2.4 cm. An idealized eye will focus an object at infinity on the retina which is located at distance, D, behind the lens of the eye. We can say that focal length varies from person to person, that is why people tend to have hypermetropia or myopia.

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Related Questions Question 1

To find the focal length of a convex mirror, a student records the following data:

Object pin: 22.2cm 22.2cm Convex lens: 32.2cm 32.2cm Convex mirror: 45.8cm 45.8cm Image pin: 71.2cm 71.2cm

The focal length of the convex lens is

f 1 f1

and that of the mirror is

f 2 f2

. Then taking index correction to be negligibly small,

f 1 f1 and f 2 f2 are close to: A. f 1 =7.8cm, f 2 =12.7cm B. f 1 =12.7cm, f 2 =7.8cm C. f 1 =7.8cm, f 2 =25.4cm D. f 1 =15.6cm, f 2 =25.4cm

A.f1=7.8cm,f2=12.7cmB.f1=12.7cm,f2=7.8cmC.f1=7.8cm,f2=25.4cmD.f1=15.6cm,f2=25.4cm

Question 2

A convex lens of focal length ‘f’ cut into parts first horizontally and then vertically. Find the focal length of part A of the lens, as shown.

A) f 2 f2 B) f f C) 4f 4f D) 2f 2f Question 3

For a spherical surface of radius of curvature R separating two media of refractive indices

μ 1 μ1 and μ 2 μ2

, the two principal focal lengths are

f 1 f1 and f 2 f2

respectively. Which one of the following relations is correct?

A. f 1 f1 = f 2 f2 B. f 1 μ 2 = f 2 μ 1 f1μ2=f2μ1 C. f 1 μ 2 =− f 2 μ 1 f1μ2=−f2μ1 D. f 1 μ 1 = f 2 μ 2 f1μ1=f2μ2 Question 4 Two identical glass ( μ g

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