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## Very important questions of ray optics

##### Very important questions of ray optics-

In this topic we will get some, Very important questions of ray optics. Students preparing for board examination must solve all the questions given below.

Very important questions of ray optics

1. Derive the mathematical relation between refractive indices μ1 and μ2 of two radii and radius of curvature R for refraction at a convex spherical surfaces. Consider the object to be a point source on the principle axis in rarer medium of refractive index  μ1 and a real image formed in the denser medium .

Light from a point source in air falls on a convex spherical glass surface of refractive index 1.5 and radius of curvature 20 cm . The distance of light source from the glass surface is 100cm . At what position the image will be formed?

2. A point object is placed in front of a double convex lens with its spherical faces of radii of curvature R1 and R2 . Show the path of rays due to refraction at first and subsequently at the second surface to obtain the formation of the real image of the object. Hence obtain the lens maker’s formula for a thin lens.

(i)   A double convex lens having both faces of the same radius of curvature has refractive index 1.5. Find out the radius of curvature of the lens required to get the focal length of 20 cm . (ii) How the focal length of the above lens changes when it is placed in liquid of refractive index (a) 1.3 (b) 1.5 and (c)2.5 .

To solve this questions students must watch this video

3. Draw the ray diagram to show the refraction of a ray of monochromatic light passing through a glass prism. Deduce the expression for the refractive index of glass in terms of angle of prism and angle of minimum deviation.

A ray of light incident on face AB of an equilateral glass prism ABC , shows minimum deviation of 300 calculate the speed of light through the prism. Also find the angle of incidence at face AB so that the emergent ray along the face AC .

4.What do you mean by the term total internal reflection also write the conditions to get the total internal reflection, define the term critical angle for a pair of media , how the critical angle is related to the refractive index of the medium. A point source is kept at the bottom of the pond 2m deep ( μ= 4/3 )draw the ray diagram and calculate the area of water surface through which light emerges out of the pond.

5. Draw a ray diagram showing the image formation of compound microscope, hence obtain the expression for magnifying power when (I) image is formed at infinity (II) image is formed at least distance of distinct vision. (a)Why must both the objective and eyepiece of a compound microscope have short wavelength? (b) while viewing through a compound microscope, why should our eyes be placed not on the eye piece but at short distance away from it for best viewing?

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6. Draw a labelled ray diagram of astronomical telescope, for(I) normal adjustment, (II) at least distance of distinct of vision. Also derive the expression for magnifying power .You are given the three lance L1 , L2 , L3 having power 3D , 6D and 10D respectively with aperture 8cm,1cm and 1cm respectively, which two lances will you use as an eyepiece and objective to construct (a) compound microscope and (b) Astronomical telescope. Give reasons.

7.Explain reflecting type telescope draw the ray diagram for (I) Newtonian and (II)Cassegrainian type telescope. Write advantages of reflecting type telescope over refracting type telescope.

8.Derive lens formula in a convex lens using suitable ray diagram 1/v -1/u = 1/f . (a) A convex les is used to obtain the image of an object on the screen 10 cm from the lens . if the magnification is 19, find the focal length of the lens. (b) An illuminated object and a screen are placed 90 cm apart. Determine the focal length and nature of the lens required to produce a clear image on the screen , twice the size of the object.

TO WATCH THE COMPLETE VIDEO OF THIS TOPIC CLICK ON THE VIDEO GIVEN BELOW-

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# Objective questions of ray optics

this assignment will provide the important Objective questions of ray optics for  students preparing for class-12th board examination and for the students preparing for JEE/NEET and other competitive examinations.

Reflection and Refraction of Light at Plane Surface ( Objective questions of ray optics)

1. When light travels from glass to air, the incident angle is and the refraction angle is .the true relation is :(a)θ 12      (b)  θ 1 (c)θ1 (d)Not predictable
2. Two mirrors are kept at 60 to each other and a body is placed in the middle.The total number of images formed is:(a)Three(b)Four (c)Five (d)Six
3. If an object is placed unsymmetrically between two plane mirrors inclined at an angle 72 ,then the total number of images formed is:(a)5   (b)4    (c)2   (d)infinite
4. If an object is placed symmetrically between two plane mirrors, inclined at an angle of 72 .than the total total number of images formed is:(a)5 (b)4 (c)2 (d)Infinite

5) A ray of light is incident on a plane mirror at an angle of incidence of 30⁰ ,the deviation

Produced by the mirror is :

(a) 30 ⁰ ( b) 60⁰

(c) 90⁰ (d) 120

6) when a ray of light enters a glass slab from air:

(a) its wavelength decreases

(b) its wavelength decreases

(c) its frequency increases

(d) neither wavelength nor frequency changes

7) When a light enters from air to water, then its:

(a) frequency increases and speed decreases

(b) frequency is the same but the wavelength is smaller in water then in air:

(c) frequency is same but wavelength in water is greater than in air

Categories

# Wave optics and optical instruments

### In this question paper we will practice the important questions of wave optics and optical instruments .

students preparing for class 12th must have to practice all questions given in the assignments “wave optics and optical instruments” , I  am sure that you will get sure benefits in your board examination .

Students can also solve important questions of ray optics . for important questions of ray optics click here-

Important questions on wave optics
and optical instrument
(***Derivations and reasoning type questions***)
1. Draw a ray diagram showing the image formation of compound microscope, hence obtain the expression for magnifying power when (I) image is formed at infinity (II) image is formed at least distance of distinct vision. (a)Why must both the objective and eyepiece of a compound microscope have short wavelength? (b) while viewing through a compound microscope, why should our eyes be placed not on the eye piece but at short distance away from it for best viewing?
2. Draw a labelled ray diagram of astronomical telescope, for(I) normal adjustment, (II) at least distance of distinct of vision. Also derive the expression for magnifying power
3. Define resolving power and limit of resolution derive the expression for resolving power for (I) microscope, (II)telescope and (III)eye.
4. Explain reflecting type telescope draw the ray diagram for (I) Newtonian and (II)Cassegrainian type telescope. Write advantages of reflecting type telescope over refracting type telescope.
5. Define wavefront . What type of wave front will emerge from a point source and distance light source? Draw a wave front coming out from a (I)prism(II)concave and convex mirror(III)concave lens and(III)convex lens .
6. State Huygens principle, using this principle draw the diagram to show how a plane wave front incident(I) At the interface of two media gets refracted when it propagates from a rarer to denser medium, and hence verified Snell’s law and (II) At a plane surface and gets reflected and hence derive law of reflection.
7. What are coherent sources of light ? Why two independent sources can’t be coherent ?why coherent sources are necessary to observing a sustained interference pattern ? How are the coherent sources are obtained in the Young’s double slit experiment?
8. What is interference of light? Write dawn the conditions to obtain the sustained interference fringe pattern. Show that the superposition of wave originating from two sources having displacement Y1 =a cosωt , Y2 =a cos(ωt+ɸ) at a point produces a resultant intensity , I=4a^2 cos^2(ɸ/2) hence write the conditions for the appearance of dark and bright fringes.(* this question may be asked as ,deduce the conditions for constructive and destructive interference and hence write the expression for the distance between two consecutive bright or dark interference)
9. Using Young’s double slit experiment obtain the conditions for gating bright and dark fringes also derive the expression for the fringe width. Also write the effect on fringe width when(I)Distance between slits increases/decreases(II) Distance between slits and the screen increases/decreases(III) Monochromatic light replaced by white light,(IV) One of slit is closed and (V) entire experimental apparatus is immersed in a liquid
10. In a single slit diffraction experiment , deduce the conditions for the central maximum and secondary maxima/minima observed in diffraction pattern . Also explain why the secondary maxima go on becoming weaker in intensity as the order increases.(I) Haw does the width of the slit affected the size of the central bright fringe?(II)When a tiny circular obstacle is placed in the path of the light from a distant source , why is a bright spot seen at the center of the shadow of the obstacle?(III) Show that the angular width of the central bright is two times the width of the first diffraction fringe (IV) If a mono chromatic source of light is replaced by white light , what change would you observe in the diffraction pattern?
11. What is unpolarised and plane polarised light? How an unpolarised light gets polarised when it passes through a polaroid. Why is the phenomenon of polarisation not observed by sound wave?
12. What are Polaroids ? how are the used to demonstrate that (a) A light wave is transverse in nature,(b) if an unpolarised light wave is incident, then light wave gets linearly polarised?
13. State and prove law of malus and Brewster’s law .What is Brewster’s angle ? when an unpolarised light is incident on a plane glass surface , what should be the angle of incidence so that the reflected and refracted rays are perpendicular to each other?

******IMPORTANT NOTICE FOR THE STUDENTS OF CLASS 12TH-

Students as we know , this year there are some changes in the pattern of  question paper  of physics for class 12th . It is informed by the cbse that there will be 20 marks objective type questions in the paper , but it is decleared    that what will be the  type question paper of physics . previously only 5 marks of questions was on the basis of objective question (one marks each) , and in the answer of these questions students has to write the answers , but this year question paper pattern is changed  , the sample paper provided by cbse is provided  here.

Categories

# Important numerical of  ray optics

### All questions given below is very important numerical of ray optics . These questions are  good for quick practice at the time of examination.

1. Suppose while sitting on a parked car , you noticed a jogger approaching towards you in the rear view mirror of R=2m . If the jogger is running towards you at the speed of 5m/s , how fast the image of the jogger moving when the jogger is (a)39m(b)29m(c)19m away.

2. A rod AB =10cm in length is placed along the principle axis of a concave              mirror having focal length equal to 10cm as shown in fig. the distance                  PB=20cm . what is the length of the image of the rod AB.

1. When an object is placed at a distance of 60 cm from a convex spherical mirror , the magnification produced is ½. Where should we place the object to get a magnification of 1/3?
2. A ray of light travelling in water is incident on water glass interface at angle 300calculate the angle of refraction. Refractive index of water and glass is 4/3 and 3/2 respectively .
3. What is apparent position of the object below a rectangular block of glass 6cm thick , if a layer of water 4cm thick is on the top of the glass ? Refractive index of glass and water with respect to air is 3/2 and 4/3 respectively.
4. Calculate the critical angle for total internal reflection of light travelling from (a) water to air(b) glass into water. Refractive index for glass and water is 3/2 and 4/3 respectively with respect to air.
5. Light from a point source in air falls on a spherical glass surface .If refractive index of glass is 1.5 and radius of curvature =20cm , the distance of light source from the glass surface is 100cm ; at what position image will formed?
6. A biconvex lens has a focal length 2/3 times the radius of curvature of either surface . Calculate the refractive index of lens material .
7. Find the radius of curvature of the convex surface of a plano-convex lens , whose focal length is 0.3m and the refractive index of the material of the lens is 1.5.
8. A screen is placed 100cm from an object . The image of the object on the screen is formed by a convex lens at two different locations , separated by distance 20cm . calculate the focal length of the lens used.
9. You are given three lenses L1 , L2,L3 each of focal length 10cm . an object is kept at 15cm in front of L1  ,  as shown in fig. the final image is formed at the focus of L3 find the separation between the lenses.
1. A convex lens made up of glass of refractive index 1.5 is dipped  , in turn ,in (a) a medium of refractive index 1.65 (b)   ) a medium of refractive index 1.33.Will it behave like converging or diverging lens in two cases, explain how focal length changes in two cases .
2. Three rays red  , green and blue are incident on a right angled prism ABC at face AB the refractive indices of the material  of the prism for red, green ,and blue are 1.39,1.44, and 1.47 respectively . Out of the three which color of ray emerge out of face AC. Trace the path of the three rays after passing through AB.
1. Draw ray diagram to show how specially designed prism make use of total internal reflection to obtain inverted image of the object by deviation of rays (a) through 900 (b) through 1800 and(c) through 00  .
2. State the conditions under which total internal reflection occurs . one face of a prism with a refracting angle of 30 , is coated with silver . A ray incident on another face at an angle of 45 is refracted and reflected from the silver coated face and retrace its path. Find the refractive index of the material of the prism.
3. A convex lens with the radii of curvature of magnitude 10 cm each , is put over a liquid layer is poured on the top of the plane mirror . A small needle with its tip on the principle axis of the lens , is moved along the axis until its inverted real image coincide with the needle  itself . The distance of the needle from the lens is measured to be 15 cm . on removing the liquid layer and repeating  the experiment  the new distance is measured to be 30cm ,what is the refractive index of the liquid?
4. Find the position of the image formed by the lens combination given in figure

1. A diverging lens of focal length f cut into two identical parts ,each forming a plano- convex lens what is the focal length of each part. How the focal length of the lens changes if it bisected axially?
2. The image of a needle placed 45cm from a lens is formed on a screen placed 90 cm on the other side of lens. Find displacement of image if object is moved 5cm away from lens.
3. A small bulb is placed at the bottom of a tank containing water to a depth of 80 cm . what is the area of the surface of water through which light of the bulb can emerge out ?Refractive index of water is 1.33 consider the bulb to be a point source.