CBSE Class 12 Physics Wave Optics Boards Questions Worksheet

 Important Questions for NCERT Class 12 Physics Wave Optics

WAVE OPTICS 

1. What is the relation of a wave front with a ray of light?

2. Does interference phenomenon reveal the nature of light waves?

3. Why do two identical bulbs do not produce interference?

4. Doppler shift due to motion of light source or observer with same velocity is identical. This is not for second source. Why?

5. Why can light waves be polarized but sound waves cannot?

6. Why is sun glasses made of Polaroid’s superior than those using coloured glasses?

7. Sketch the wave front emerging from a pt source of light, linear source of light like a slit.

8. State Huygens’s principle.

9. Two coherent sources of intensity ration 4: 1 interfere. Obtain the ration of intensity between the maxima and minima in the interference pattern. Ans: 9 : 1

10. The refractive index of a medium is 3 . What is the angle of refraction, if the unpolarized light is incident on it at the polarizing angle of the medium? Ans: r = 300

11. What is the polarizing angle of a medium of refractive index 1.732? Ans: ip = 600

12. Why is diffraction pattern invisible when the slit is very wide?

13. Why is coloured spectrum seen when we look through a muslin cloth? 2/3 mark type

14. If white light is used in Young’s experiment, what kind of pattern will be observed?

15. A source of red light (λ = 7000 Å) produces interference through two slits placed at a distance of 0.01 cm. at what distance should a screen be placed from the slits so that interference bands are spaced 0.1m apart?

16. The slits in Young’s experiment have width in ratio 1:16. Deduce ratio of maxima & minima in interference pattern. Ans: 2.78

17. Yellow light (λ = 6 x 10 -7) illuminates single slit whose width is 1 x 10 -4 m. What is the distance between two dark lines on either side of the central maximum if the diffraction pattern is viewed on a screen that is 1.5m from the slit? Ans: 18mm

18. Using Huygens’s principle, draw a diagram to show propagation of a wave front originating from a monochromatic pt source.

19. Using Huygens’s principle, derive Snell’s law

20. In Young’s experiment, the width of the fringes obtained with light of wavelength 6000 Å is 2.0mm. Calculate the fringe width if the entire apparatus is immersed in a liquid medium of refractive index 1.33. Ans: 1.503mm

21. Determine the angular separation between central maximum & first order maximum of the diffraction pattern due to a slit of width 0.25mm when light of wavelength 5890 Å is incident on it normally. Ans: 3.534 x 10 -3 rad

22. How are Polaroids artificially made? Mention two uses of Polaroids. Draw a graph showing the dependence of intensity of transmitted light on the angle between polarizes & analyzer.

23. A slit of width ‘d’ is illuminated by light of wavelength 6500 Å. For what values of ‘d’ will the
(i) First min fall at an angle of diffraction of 300?
(ii) First max. fall at an angle of diffraction of 300?

24. In a single slit diffraction pattern, how does the angular width of the central maximum vary, when
(i) aperture of slit is increased
(ii) distance between the slit and screen is decreased
(iii) monochromatic visible light of larger wavelength is used?    
Justify your answer in each case.

Important Questions for NCERT Class 12 Physics Wave Optics

Question. In the Young’s double slit experiment, the intensity of light at a point on the screen where the path difference l is K, (l being the wavelength of light used). The intensity at a point where the path difference is l/4 will be
(a) K
(b) K/4
(c) K/2
(d) zero  

Question. In Young’s double slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelengths l1 = 12000 Å and l2 = 10000 Å. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other?
(a) 4 mm
(b) 3 mm
(c) 8 mm
(d) 6 mm  

Question. In Young’s double slit experiment the distance between the slits and the screen is doubled. The separation between the slits is reduced to half. As a result the fringe width
(a) is halved
(b) becomes four times
(c) remains unchanged
(d) is doubled.  

Question. Colours appear on a thin soap film and on soap bubbles due to the phenomenon of
(a) interference
(b) dispersion
(c) refraction
(d) diffraction.  

Question. In a Fresnel biprism experiment, the two positions of lens give separation between the slits as 16 cm and 9 cm respectively. What is the actual distance of separation?
(a) 13 cm
(b) 14 cm
(c) 12.5 cm
(d) 12 cm 

Question. Interference was observed in interference chamber where air was present, now the chamber is evacuated, and if the same light is used, a careful observer will see
(a) no interference
(b) interference with brighter bands
(c) interference with dark bands
(d) interference with larger width.  

Question. If yellow light emitted by sodium lamp in Young’s double slit experiment is replaced by monochromatic blue light of the same intensity
(a) fringe width will decrease
(b) fringe width will increase
(c) fringe width will remain unchanged
(d) fringes will becomes less intense 

Question. In Young’s double slit experiment carried out with light of wavelength (l) = 5000 Å, the distance between the slits is 0.2 mm and the screen is at 200 cm from the slits. The central maximum is at x = 0. The third maximum (taking the central maximum as zeroth maximum) will be at x equal to
(a) 1.67 cm
(b) 1.5 cm
(c) 0.5 cm
(d) 5.0 cm  

Question. In Young’s experiment, two coherent sources are placed 0.90 mm apart and fringes are observed one metre away. If it produces second dark fringe at a distance of 1 mm from central fringe, the wavelength of monochromatic light is used would be
(a) 60 × 10^–4 cm
(b) 10 × 10^–4 cm
(c) 10 × 10^–5 cm
(d) 6 × 10^–5 cm  

Question. In Young’s double slit experiment, the fringes width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4/3 , without disturbing the geometrical arrangement, the new fringe width will be
(a) 0.30 mm
(b) 0.40 mm
(c) 0.53 mm
(d) 450 micron. 

Question. Assume that light of wavelength 600 nm is coming from a star. The limit of resolution of telescope whose objective has a diameter of 2 m is
(a) 3.66 × 10^–7 rad
(b) 1.83 × 10^–7 rad
(c) 7.32 × 10^–7 rad
(d) 6.00 × 10^–7 rad 

Question. An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
(a) small focal length and large diameter
(b) large focal length and small diameter
(c) large focal length and large diameter
(d) small focal length and small diameter. 

Question. The ratio of resolving powers of an optical microscope for two wavelengths l1 = 4000 Å and l2 = 6000 Å is
(a) 9 : 4
(b) 3 : 2
(c) 16 : 81
(d) 8 : 27 

Question. A linear aperture whose width is 0.02 cm is placed immediately in front of a lens of focal length 60 cm.
The aperture is illuminated normally by a parallel beam of wavelength 5 × 10^–5 cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is
(a) 0.10 cm
(b) 0.25 cm
(c) 0.20 cm
(d) 0.15 cm 

Question. In a double slit experiment, the two slits are 1 mm apart and the screen is placed 1 m away. A monochromatic light of wavelength 500 nm is used.
What will be the width of each slit for obtaining ten maxima of double slit within the central maxima of single slit pattern?
(a) 0.5 mm
(b) 0.02 mm
(c) 0.2 mm
(d) 0.1 mm 

Question. At the first minimum adjacent to the central maximum of a single-slit diffraction pattern, the phase difference between the Huygen’s wavelet from the edge of the slit and the wavelet from the midpoint of the slit is
(a) Π radian
(b) Π /8 radian
(c) Π /4 radian
(d) Π/2 radian  

Question. A beam of light of l = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is
(a) 1.2 cm
(b) 1.2 mm
(c) 2.4 cm
(d) 2.4 mm 

Question. A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?
(a) The angular width of the central maximum will decrease.
(b) The angular width of the central maximum will be unaffected.
(c) Diffraction pattern is not observed on the screen in the case of electrons.
(d) The angular width of the central maximum of the diffraction pattern will increase. 

Question. A parallel beam of light of wavelength l is incident normally on a narrow slit. A diffraction pattern formed on a screen placed perpendicular to the direction of the incident beam. At the second minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of slit is
(a) 2Π
(b) 3Π
(c) 4Π
(d) Πl 

Question. The angular resolution of a 10 cm diameter telescope at a wavelength of 5000 Å is of the order of
(a) 10⁶ rad
(b) 10^–2 rad
(c) 10^–4 rad
(d) 10^–6 rad 

Question. A telescope has an objective lens of 10 cm diameter and is situated at a distance of one kilometre from two objects. The minimum distance between these two objects, which can be resolved by the telescope, when the mean wavelength of light is 5000 Å, is of the order of
(a) 0.5 m
(b) 5 m
(c) 5 mm
(d) 5 cm  

Question. Diameter of human eye lens is 2 mm. What will be the minimum distance between two points to resolve them, which are situated at a distance of 50 meter from eye? (The wavelength of light is 5000 Å.)
(a) 2.32 m
(b) 4.28 mm
(c) 1.25 cm
(d) 12.48 cm 

Question. Ray optics is valid, when characteristic dimensions are
(a) much smaller than the wavelength of light
(b) of the same order as the wavelength of light
(c) of the order of one millimetre
(d) much larger than the wavelength of light. 

Question. A parallel beam of monochromatic light of wavelength 5000 Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed in focal plane.
The first minimum will be formed for the angle of diffraction equal to
(a) 0°
(b) 15°
(c) 30°
(d) 50° 

Question. The Brewsters angle ib for an interface should be
(a) 0° < ib < 30°
(b) 30° < ib < 45°
(c) 45° < ib < 90°
(d) ib = 90 

Question. A parallel beam of monochromatic light of wavelength 5000 Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed in focal plane.  
The first minimum will be formed for the angle of diffraction equal to      
(a) 0°
(b) 15°
(c) 30°
(d) 50°

Answer   C

Question. The Brewsters angle ib for an interface should be   
(a) 0° < ib < 30°
(b) 30° < ib < 45°
(c) 45° < ib < 90°
(d) ib = 90° 

Answer   C

Question. In a diffraction pattern due to a single slit of width a, the first minimum is observed at an angle 30° when light of wavelength 5000 Å is incident on the slit.    
The first secondary maximum is observed at an angle of
(a) sin⁻¹ (1/2)
(b) sin⁻¹ (3/4)
(c) sin⁻¹ (1/4)
(d) sin⁻¹ (2/3)

Answer   B

Wave optics-Interference

Test Paper-I

QUESTION ANSWER PAGE

1 Give the property of light that forms the basis of ray optics 

2 Show the following by drawing a diagram
a. Plane wave front from a spherical wave front
b. Light diverging from a point source
c. The portion of the wave front of light from a distant star intercepted by the Earth 

3 State Huygens Principle of wave fronts 

4 Differentiate between a ray and a wave front. 

5 Show how a plane wave gets reflected from a surface. Hence, verify laws of reflection. 

6 Show how a plane wave gets refracted as it travels from one medium to another. Also verify the laws of refraction using the same. 

7 Show the following by drawing a ray diagram
Refraction of a plane wave by
a. Thin prism
b. A convex lens 
c. Concave mirror

8 When monochromatic light is incident on a surface separating two media, the reflected and refracted light both have the same frequency as the incident frequency. Explain why?

9 When light travels from a rarer to a denser medium, the speed decreases. Does the reduction in speed imply a reduction in the energy carried by the light wave?

10 In the wave picture of light, intensity of light is determined by the square of the amplitude of the wave. What determines the intensity of light in the photon picture of light?

11 State superposition principle. Give the conditions for constructive interference and destructive interference.

12 What is meant by interference? What type of waves produce the interference

13 Give the relationship between the intensity and amplitude.

14 Describe Young’s double slit experiment to produce interference pattern due to a monochromatic source of light. Deduce the expression for the fringe width.

Wave optics-Test Paper-II

QUESTION ANSWER PAGE

1 a. Plot the graph showing the intensity distribution in case of Young’s double slit experiment.
b. Two slits are made 1mm apart and the screen is placed one metre away. What is the fringe separation when blue-green light of wavelength 500 nm is used?

2 What is the effect on the interference fringes in a Young’s double slit experiment due to each of the following operations.
a. The screen is moved away from the plane of the slits.
b. The source is replaced by another source of shorter wavelength
c. The separation between the two slits is increased

3 What is the effect on the interference fringes in a Young’s double slit experiment due to each of the following operations.
a. The source slit is moved closer to the double-slit plane
b. The width of the source slit is increased
c. The monochromatic source is replaced by a source of white light?

4 a. What is a polarised wave and an unpolarised wave?
b. What is the Brewster angle for air to glass transition?
(refractive index of glass = 1.5)

5 State Malus Law. Discuss the intensity of transmitted light when a polaroid sheet is rotated between two crossed polaroids?

6 State Brewster’s Law. 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? 

7 What are coherent sources? Why are they necessary for observing a sustained interference pattern? How are the two coherent sources obtained in the Young’s double slit experiment? 

8 What is the shape of the locus of the point P lying in the x-y plane such that S2P-S1P= is a constant? Give reason why the fringe pattern appears to be straight lines. 

9 What is meant by Interference? How can you produce interference?

10 Explain through an experiment light exhibits the property of polarization.

11 Give the condition to find out the path difference between the waves to produce constructive interference and destructive interference. Also give any two difference between constructive interference and destructive interference.

Wave optics

Test Paper-III-Diffraction

QUESTION ANSWER PAGE

1 What is meant by diffraction? Give the condition under which diffraction can be felt?

2 How will you obtain diffraction pattern? Give the conditions for obtaining the maximum intensity and minimum intensity in case of diffraction. Also give the graphical representation of diffraction. 

3 Give the differences interference and diffraction. 

4 What is the size of the central maximum when a converging lens of focal length f is placed in the path of the light coming from the two slits and the screen is placed at the focal length of the lens? Also what is the angular separation of the central maximum from the first dark fringe of the diffraction pattern? 

5 Name the factor on which the angular resolution of the telescope depends upon.

6 What is the effect of diffraction on a beam falling on a lens?

7 Two slits are made one millimeter apart and the screen is placed one metre away. What should the width of each slit be to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern?

8 What is the radius of the central bright maximum formed by a single –slit diffraction pattern formed in the focal plane of a lens?

9 Draw a diagram showing the diffraction effects on a parallel beam of light incident on a convex lens 

10 Assume that light of wavelength 6000 Aᶱ is coming from a star. What is the limit of resolution of a telescope whose objective has a diameter of 254cm? 

11 Define The resolving power of a microscope and derive an expression for finding the same. 

12 What is Fresnel distance? What is the importance of it? Give an expression to find the same. 

13 For what distance is ray optics a good approximation when the aperture is 3mm and the wavelength is 500nm? 

14 Two students are separated by a 7m partition wall in a room 10m high. If both light and sound waves can bend around obstacles, how is it that the students are unable to see each other even though they can converse easily?