DIFFRACTION GRATING - Q17

17) What are the uses of a diffraction grating?

Ans: The following are uses of diffraction grating:

• The diffraction grating is an immensely useful tool for the separation of the spectral lines associated with atomic transitions.
• It acts as a "super prism", separating the different colors of light much more than the dispersion effect in a prism.
• The rainbow-like iridescent reflection on CDs, DVDs, and bluray discs is an example of diffraction grating.
• Diffraction gratings are extremely useful in study of structure of atoms and molecules, investigating the composition of stars.
• Diffraction grating is used in Spectrometers, Monochromators, Holograms, Fiber-optic Communications, Optical Storage Mediums, Lasers, and Light Polarization Devices etc.

DIFFRACTION GRATING - Q16

16) How can you experimentally verify that the incident rays are normal to the grating surface?

Ans: Rotate the screw of observing telescope so as to move eyepiece front and back. If the slit image doesn’t move along cross wire, then the incident rays are normal to grating surface. Otherwise, incident rays are not normal to the grating surface.

DIFFRACTION GRATING - Q15

15) What do you mean by the resolving power of a grating?

Ans: Chromatic resolving power of a grating is defined as its

power of distinguishing two nearby spectral lines and is defined as

DIFFRACTION GRATING - Q14

14) What happens if the ruled surface of the grating faces the

collimator?

Ans: Lines will be formed at opposite side of observer if the ruled

surface of the grating faces the collimator due to reflection.

DIFFRACTION GRATING - Q13

13) What is the SI unit of wavelength?

Ans: SI unit of wavelength is meter (m).

DIFFRACTION GRATING - Q12

12) What will happen if the rulings of the grating are not parallel and the distance between two consecutive rulings is not constant?

Ans: In this case also diffraction occurs but an irregular fringe pattern will be formed. The calculations and representations may be quite complicated.

DIFFRACTION GRATING - Q11

11) What will happen if the slit is illuminated with white

light?

Ans: If the slit is illuminated with white light, a single maximum can form a spectrum showing a rainbow of colors, as light of different wavelengths will have maxima and minima at different angles.

DIFFRACTION GRATING - Q10

10) Distinguish between a grating spectrum and a prismatic

spectrum.

Ans: Grating spectrum is a spectrum produced as a result of diffraction by a grating whereas; prismatic spectrum is a consequence of dispersion of light by a prism.

• In grating spectrum we can observe different orders of spectral lines on either side of spectrum which do not happen in prismatic spectrum.
• The prism spectrum is brighter than grating spectra.
• In case of a prism, the deviation is least for red and greatest for violet. While, in case of grating, deviation is least for violet and greatest for red. Hence, in prism spectrum, spectral colors are in order from red to violet. But in grating spectrum, spectral colors are in order from violet to red.
• Prism spectrum depends on nature of material of prism but grating spectra do not depend on material of grating.
• Resolving power of grating spectra is large. And that of prismatic spectrum is small.

DIFFRACTION GRATING - Q9

9) How does the angular dispersive power of the grating vary with (i) the order number n of the spectrum, (ii) the grating element or the number of lines per cm in the grating, and (iii) the wavelength λ?

Ans: 

Order number n of the spectrum:

Angular dispersive power of the grating is proportional to n.

Angular dispersive power increases with increase in n.

Grating element or the number of lines per cm in the grating:

Angular dispersive power of the grating is inversely proportional to the grating element.

Angular dispersive power of the grating is proportional to the number of lines per cm in the grating

Wavelength λ:

Angular dispersive power of the grating is independent of wavelength.

DIFFRACTION GRATING - Q8

8) What do you understand by the angular dispersive power

of the grating?

Ans: The angular dispersion or dispersive power of a grating is defined as the rate of change of angle of diffraction with the change of wavelength in a particular order of the spectrum.

DIFFRACTION GRATING - Q7

7) What is the effect of increasing the number of lines per cm
on the grating?
Ans: Resolving power increases if number of lines per cm on the grating increases. i.e., nearby spectral lines can be distinguished clearly.

DIFFRACTION GRATING - Q6

6) Define grating element and corresponding points.
Ans: Distance between two consecutive slits (lines) of a grating is
called grating element. If 'a' is the separation between two slits and
'b' is the width of a slit, then grating element 'd' is given by;

d = a + b    [or]  d = length of grating/no. of lines

DIFFRACTION GRATING - Q5

5) What type of grating do you use for your experiment?
Ans: Plane transmission diffraction grating is used in the experiment.

DIFFRACTION GRATING - Q4

4) How are commercial gratings made?
Ans: A diffraction grating is made by making many parallel scratches on the surface of a flat piece of transparent material. It is possible to put a large number of scratches per centimeter on the material. The scratches are opaque but the areas between the scratches can transmit light. Gratings used to disperse ultraviolet (UV) and visible light usually contain between 300 and 3000 grooves per millimeter, so the distance between adjacent grooves is on the order of one micron.

DIFFRACTION GRATING - Q3

3) What is a reflection grating?
Ans: A diffraction grating in which the grooves are ruled in a reflective coating. The grating may be either plane or concave, the latter being able to focus light. The incident and diffracted rays lies on same side of the grating.

DIFFRACTION GRATING - Q2

2) What is a plane transmission diffraction grating?
Ans:
Diffraction by a plane transmission grating:

A beam of monochromatic light of wavelength λ is incident on a grating at angle α to the grating normal, and diffracted along several discrete paths {βm}, for diffraction orders {m}. The incident and diffracted rays lies on opposite sides of the grating. The configuration shown, in which the transmission grating is illuminated from the back, is most common.

DIFFRACTION GRATING - Q1

1) In this experiment, how does diffraction occur?
Ans: A diffraction grating is made by making many parallel scratches on the surface of a flat piece of transparent material. It is possible to put a large number of scratches per centimeter on the material. The scratches are opaque but the areas between the scratches can transmit light. Thus, a diffraction grating becomes a multitude of parallel slit sources when light falls upon it. A parallel beam of monochromatic light is incident normally on the face of a plane transmission diffraction grating, bright diffraction maxima are observed on the other side of the grating.