MCQs

1. [2079 ‘O’] In Fraunhofer diffraction, the incident wave front should be,
   a. elliptical
   b. plane
   c. spherical
   d. cylindrical
2. [2079 ‘V’] A diffraction grating has 400 lines/mm and is illuminated normally by a monochromatic light of wave length 6000 Å. The maximum number of diffraction maxima obtained will be
   a. 4.16
   b. 4
   c. 5
   d. 2.96

Answers

1.b

2.b

THEORETICAL QUESTIONS

New Course

1. [2081 GIE ‘A’] Discuss the diffraction of light through a single slit. [3]
2. [2080 GIE ‘A’] Suppose a monochromatic light of wavelength [latex]’\lambda'[/latex] is incident normally on a narrow slit of width ‘d’ and focussed on a screen. Derive condition for the first minimum of intensity on the screen in terms of wavelength [latex]\lambda[/latex] and angle of diffraction [latex]’\theta'[/latex]. [2]
3. [2080 GIE ‘B’] Distinguish between interference and diffraction. [2]
4. [2080 ‘P’] What is diffraction of light? [1]
5. [2079 GIE ‘A’]

1. Explain diffraction pattern due to a single slit and derive condition for secondary maxima and minima. [4]
2. Give two differences between fringes formed in single slit diffraction and young’s double slit experiment. [2]

Old Course

SHORT ANSWER QUESTION

6. [2078 ‘C’] Distinguish between Fresnel diffraction and Fraunhofer diffraction.
7. [2074 ‘S’] Why is diffraction of sound waves easier to observe than that of light waves?
8. [2072 ‘S’] Light waves undergo diffraction around an edge. Can sound wave different around an edge? Explain.

LONG ANSWER QUESTION

9. [2076 GIE ‘A’] Describe the diffraction of light through a single slit. Find the conditions of formation of maxima and minima.
10. [2076 ‘C’, 2075 ‘S’, 2075 ‘B’] Discuss Fraunhofer’s diffraction at a single slit.

OR [2073 ‘D’] What is diffraction of light? Explain the case of diffraction at a single slit. Hence show the intensity distribution in the figure.

OR [2073 ‘S’] Describe the diffraction of light at a single slit and find the condition for secondary maxima and minima.

11. [2074 ‘A’] What is diffraction grating? Discuss the formation of diffraction pattern due to a diffraction grating.
12. [2074 ‘B’] Describe Fraunhofer’s diffraction at a single slit.
13. [2072 ‘C’, 2072 ‘D’] Define Fraunhofer diffraction. How is transmission grating constructed? Describe necessary theory of diffraction grating.
14. [2072 ‘E’] What do you mean by diffraction of light? Explain the diffraction pattern due to single slit to find the angular width of the central band.

NUMERICAL PROBLEMS

New Course

1. [2082] A parallel beam of monochromatic light is incident on diffraction grating having 500 lines/mm to get second order maxima at 30^o. Calculate the wavelength of light used. [3] Ans: [latex]5\times 10^{-7}[/latex] m
2. [2081 GIE ‘B’] A diffraction grating has 600 lines per mm and is illuminated normally by monochromatic light of wavelength 700 nm. Calculate the diffracting angle for first order spectrum and the maximum number of orders that will be visible. [3] Ans: 24.83^o, 2
3. [2081 B/C] A monochromatic light of wavelength 5890 Å is incident normally on a diffraction grating which has 6000 lines per centimeter.

1. At what angle will the second order image be seen? [2]
2. Is third order image possible with this grating? [1] Ans: (i) 45^o (ii) Not possible

4. [2081 ‘D’] How wide is the central diffraction peak on a screen 3.5m behind a 0.01mm slit illuminated by 500nm light? [3] Ans: 0.35 m
5. [2080 GIE ‘A’] A plane transmission grating has 500 lines per mm and the second order spectral line is refracted 30^o. Calculate the wavelength of light used. [3] Ans: [latex]5\times 10^{-7}[/latex] m
6. [2080 GIE ‘B’] For a certain grating a second order green line is found at 41^o. At what angle will a first order yellow line be found? Wavelength of green light is 546nm and that of yellow light is 589nm. [3] Ans: 20.8^o
7. [2080 ‘P’] Calculate the width of central diffraction peak on a screen 4 m behind a 0.01 m slit illuminated by 600 nm light source. [2] Ans: [latex]1.2\times 10^{-4}[/latex] m
8. [2080 ‘R’] A plane transmission grating has 5000 lines per cm and the second order spectral line is diffracted through 30^o. Calculate the wavelength of light used. [2] Ans: [latex]5\times 10^{-7}[/latex] m

Old Course

9. [2078 ‘C’] In a plane transmission grating, the angle of diffraction for the second order maximum for the wavelength [latex]5\times 10^{-7}[/latex] is 30^o. Calculate the number of lines in one cm of the grating surface. Ans: 4000 lines/cm
10. [2076 GIE ‘B’] How wide is the central diffraction peak on a screen 5 m behind 0.010 mm slit illuminated by 450 nm light? Ans: 0.45 m
11. [2076 ‘B’] How wide is the central diffraction peak on a screen 5 m behind a 0.01 mm slit illuminated by 500 nm light source? Ans: 0.5 m
12. [2075 ‘A’] How wide is the central diffraction peak on a screen 3.5 m behind a 0.01 mm slit illuminated by 500 nm light source? Ans: 0.35 m
13. [2073 ‘C’] A plane transmission grating having 500 lines per mm is illuminated normally by light source of 600 nm wavelength. How many diffraction maxima will be observed on a screen behind the grating? Ans: 3