Diffraction Of Light (Board Level)

1.

State Huygens principle of diffraction of light.

2.

In deriving the single slit diffraction pattern, it was stated that the intensity is zero at angles of   n \displaystyle \lambda /a. Justify this by suitably dividing the slit to bring out the cancellation.

3.

Explain what is meant by diffraction of light.  Describe a simple experiment to demonstrate diffraction at a single slit.

4.

State three characteristic features which distinguish the interference pattern due to two coherently illuminated sources as compared to that observed in a diffraction pattern due to a single slit.

5.

For a given single slit, the diffraction pattern is obtained on a fixed screen, first by using red light and then with blue light.  In which case, will the central maxima, in the observed diffraction pattern, have a larger angular width ?

6.

How does the angular separation between fringes in single-slit diffraction experiment change when the distance of separation between the slit and screen is doubled ?

7.

In a single-slit diffraction experiment, the width of the slit double the original width.  How does this affect the size and of the central diffraction band ?

8.

In single slit diffraction experiment, yellow light is replaced by X-ray.  How will the diffraction pattern be affected?

9.

A single slit diffraction experiment is immersed completely in water without changing any other parameter. How is width of central maximum affected?

10.

Coloured spectrum is seen when we look through a muslia cloth.  Why?

11.

In a single slit diffraction experiment, a monochromatic source of light of wavelength  illuminates a narrow slit of width a.  Show, giving appropriate reasoning, that the half angular width of the central maximum in the observed pattern is (nearly) equal to \displaystyle \lambda /a.

12.

Answer the following questions :            

(i) In what way is diffraction from each slit related to the interference pattern in a double slit experiment ?

(ii) When a tiny circular obstacle is placed in the path of light from a distance source, a bright spot is seen at the centre of the shadow of the obstacle.  Explain, why.

13.

Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wavelength 400 nm.

14.

A diffraction grating has 5000 lines per cm.  What is the grating element?

15.

How does the angular width of principal maximum in the diffraction pattern vary with the width of slit?

16.

In a single slit diffraction experiment, the width of the slit is made double the original width.  How does this affect the size and intensity of the central diffraction band? Draw a plot of the intensity distribution.

17.

In a single slit diffraction experiment, when a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle.  Explain why ? State two points of difference between the interference pattern obtained in Young’s double slit experiment and the diffraction pattern due to a single slit.

20.

(a) 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 the screen is decreased ? Justify your answer in each case.

 (b) How is the diffraction pattern different from the interference pattern obtained in Young’s double slit experiment ?

21.

Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

22.

A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the first minimum is at a distance of 2.5 mm from the centre of the screen. Find the width of the slit.

23.

(a) In a single narrow slit (illuminated by a monochromatic source) diffraction experiment, deduce the conditions for the central maximum and secondary maxima and minima observed in the diffraction pattern.  Also explain why the secondary maxima go on becoming weaker in intensity as the order increases.

(b) Answer the following questions :

How does the width of the slit affect the size of the central diffraction band ?When a tiny circular obstacle is placed in the path of light from a distant source, why is a bright spot seen at the centre of the shadow of the obstacle ?

24.

Answer the following questions:

(a) In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction  band?

(b) In what way is diffraction from each slit related to the interference pattern in a double-slit experiment?

(c) When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

(d) Two students are separated by a 7 m partition wall in a room 10 m 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.

(e) Ray optics is based on the assumption that light travels in a straight line.Diffraction effects (observed when light propagates through small apertures/slits or around small obstacles) disprove this assumption. Yet the ray optics assumption isso commonly used   in understanding location and several other properties of images in optical instruments. What is the justification?

25.

Define resolving power of a compound microscope.  How does the resolving power of a compound microscope change when

(i)Refractive index of the medium between the object and objective lens increases?

(ii) Wavelength of the radiation used is increased?