# 11th Class Physics Chapter 10 Optical instruments Short Questions Answer

## 11th Class Physics Chapter 10 Optical instruments Short Questions Answer

We are providing all Students from 5th class to master level all exams preparation in free of cost. Now we have another milestone achieved, providing all School level students to the point and exam oriented preparation question answers for all science and arts students.

After Online tests for all subjects now it’s time to prepare the next level for Punjab board students to prepare their short question section here. We have a complete collection of all classes subject wise and chapter wise thousands questions with the right answer for easy understanding.

Here we are providing complete chapter wise Physics questions and Answers for the 11th class students. All the visitors can prepare for their 11th class examination by attempting below given question answers.

In this List we have included all Punjab boards and both Arts and Science students. These Boards students can prepare their exam easily with these short question answer section

Lahore Board 11th classes short questions Answer

Rawalpindi Board 11th classes short questions Answer

Gujranwala Board 11th classes short questions Answer

Multan Board 11th classes short questions Answer

Sargodha Board 11th classes short questions Answer

Faisalabad Board 11th classes short questions Answer

Sahiwal Board 11th classes short questions Answer

DG Khan Board 11th classes short questions Answer

Bahwalpur Board 11th classes short questions Answer

All above mention Punjab Boards students prepare their annual and classes test from these online test and Short question answer series. In coming days we have many other plans to provide all kinds of other preparation on our Gotest website.

How to Prepare Punjab Board Classes Short Question Answer at Gotest

- Just Open the desired Class and subject which you want to prepare.
- You have Green bars which are Questions of that subject Chapter. Just click on Bar, it slides down and you can get the right answer to those questions.
- You can also Rate those question Answers with Helpful or not to make it more accurate. We will review all answers very carefully and also update time to time.

Now you can start your preparation here below

**Solution:-**

Magnification produced by the objective is

M

_{1 =}5

Magnification produced by the eye-piece is

M

_{2}= 50

The total magnification ‘M’ produced by the objective and eye-piece of the compound microscope is equal to the product of M

_{1}and M

_{2}. That is

M= M

_{1}M

_{2}

Putting the values of M

_{1}and M

_{2}, we get

M=5*50= 250

M= 250

M = L/f

_{0}(1+ d/f

_{e}) ……………………… (1)

Where f

_{0}= focal length of objective lens

f

_{e}= focal length of eye piece

L= Length of compound microscope

d= Least distance of distinat vision

It is clear from the above relation that smaller the focal length, greater will be the magnifying power (i.e. M α 1/f). therefore, in order to increase the magnifying power of microscope and objective of short focal length is used.

The purpose of an microscope or telescope is not only to magnify an object but to reveal (show) it in great detail. The amount of detail revealed by an optical instrument depends on what is called resolving power.

Mathematically it is expressed as

α

_{min}=1.22 λ/D

This equation shows that greater the diameter (aperture) of the convex lens and smaller value of the wave length of light, higher will be resolving power of the optical instrument.

Mathematically, it is expressed as

sinθ

_{1}/sinθ

_{2 }= n

_{2}/n

_{1}

or n

_{1}sinθ

_{1}= n

_{2}sinθ

_{2}

It can be expressed as

Magnifying power = Angle subtended by image/Angle subtended by the object

Or M= θ

_{l}/θ

_{0}= B/α

When a ray of light travel from a denser medium (glass) to a rarer medium (air) it bends away from the normal. The angle of incidence for which angle of refraction is 90^{0} is called critical angle. It is denoted by θ_{c}

**Formula:-
** According to snell’s law

n

_{1}sinθ

_{1}= n

_{2}sinθ

_{2}

θ

_{1}= θ

_{c},θ

_{2}=90

^{0}

when

Therefore,

n

_{1}sinθ

_{c}= n

_{2}sin 90

^{0}

or n

_{1}sinθ

_{c}= n

_{2 }(sin 90

^{0}= 1)

or sin θ

_{c}= n

^{2}/n

_{1}

**Power of a lens:-**

The reciprocal of the focal length of a lens expressed in metres is called the power of a lens. It is denoted by D. That is

D= 1/f

**Unit of power:-**

The unit of power of a len is dioptre.

**Definition of dioptre:-**

One dioptre is the power of a lens of one meter focal length.

Thus,

D= 1/focal length of the lens in meter=1/f

The power of a convex lens is positive while that of concave is nagitive.

Magnifying power of a compound microscope is given by the formula

M = q/p ( 1+ d/f

_{e})

The total length of the blue is given by

L = f_{0} + f_{e}

putting the value, we have

24 = f_{0}+f_{e} ………………………… (2)

Magnifying power = M= f_{0}/f_{e} or 5 = f_{o}/f_{e
}Or f_{o}= 5f_{e} ………………………….(3)

putting the value of f_{0} from equ (3) in equ (2) we get

24 = 5f_{e}+ f_{e}

or 6f_{e} = 24

f_{e} = 4cm …………………(4)

Putting the value of f_{e }in equ (2)

24= f_{o} + 4

or f_{0} =24 -4= 20 cm

F_{0} = 20 cm

**Convex lens.
**A lens which converges a beam of parallel rays to a point after refraction is called convex lens(or conversing lens)

A lens which is thicker in the center (middle) and thinner at the edges is called a convex lens or converging lens.

This lens produces a real image whose sign is positive.

**Concave lens :-**

A lens which diverges a beam of parallel rays after refraction is called concave lens(or diverging lens)

A lens which is thinner at the center and thicker at the edges is called a concave or diverging lens.

A concave lens produces a virtual image whose sign is taken as negative.

The refractive (u) of prism can be found by using the formula

u = sin(A+D

_{m})/2/ sin A/2

where ‘A’ is the angle of prism and D

_{m}is the angle of minimum deviation.

It consists of three main parts.

(i) A collimator

(ii) A Turntable

(iii) A Telescope

**Uses:-**

(1) It is used to fined the wavelength of light.

(2) It is also used to fined the refractive index of transparent material (i.e. prism)

(3)It is used to study the spectra of different sources of light.

Have any other short question related to this 11th Class Physics Chapter 10 Optical instruments please write down in comment section.