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11th Class Chapter nine Physics Short Questions

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Question: 1
What do you mean by the term wavefront and ray of light?
Answer: 1
1-35
Such a surface on which all the points have same phase of vibration is known as wavefront.
A line normal to wavefront including the direction of motion is called a ray of light.
Question: 2
Under what conditions two or more sources of light behave as coherent sources?
Answer: 2
2-35
Toe or more sources of light behave as coherent sources if
  1. They emit monochromatic wave.
  2. They are phase coherent.
Question: 3
What are conditions for detectable interference of light?
Answer: 3
3-35
For detectable interference,light beam should be
  • Monochromatic
  • Coherent
Question: 4
In Young's experiment, one of the slits is covered with blue filter and other red filter, what would be the pattern of light intensity on the screen?
Answer: 4
4-35
No interference pattern will be observed because blu and red lights are of different wavelengths. So the source of light will not be coherent
Question: 5
Explain whether the Young's experiment is an experiment for studying interference or diffraction effect of light.
Answer: 5
5-35
Mainly, Young's experiment was performed to study the interference of light.However, it also involves diffraction.So diffraction can also be studied by this experiment because when light passes through the slit, it bends towards the corner.
Question: 6
Write two steps of Huygen's principle.
Answer: 6
6-35
  1. Each point of a wave front may be considered as a source of secondary wavelets.
  2. The new position of the wave front after a certain interval of time can be found by constructing a surface that touches all the secondary wavelets.
Question: 7
What condition must be met by interfering beams to observe the phenomena of interference?
Answer: 7
7-35
The following conditions must be met, in order to observe the phenomenon.
  1. The interfering beams must be monochromatic, that is, of a single wavelength.
  2. The interfering beams of light must be coherent.
Question: 8
Can visible light produce interference fringes? Explain.
Answer: 8
8-35
Yes visible light or what light can produce interference fringes. But each color will produce its own interference fringe pattern. Theses patterns overlap to give rise to a resultant diffused coloured interference pattern.
Question: 9
How can the distance between interference fringes affect by the separation between the slits of young's experiment? Can fringes disappear?
Answer: 9
9-35
Alternate Text
Question: 10
How will you increase the fringe width in young's double slit experiment?
Answer: 10
10-35
Alternate Text
Question: 11
Define wave front and spherical wave front.
Answer: 11
11-35
Wave Front: Such a surface on which all the points have same phase of vibration is known as wavefront.

Spherical wave fronts: If a point source is sending out waves in three dimensions, the wave fronts are spheres centered on the source. Such wave fronts are called a spherical wave fronts.
Question: 12
If white light is incident on a film of irregular thickness at all possible angles,what will be the pattern of interference fringes? Explain your answer.
Answer: 12
12-35
If white light is incident on a film of irregular thickness at all possible angles, we should consider the interference pattern due to each spectral colour separately. If at a certain place condition of destructive interference of one colour is satisfied then that portion of film will exhibit the remaining constituent colours of white light.
Question: 13
In Newton's rings, Why are the fringes circular?
Answer: 13
13-35
The thickness of the air film between plano-convex lens and plane glass plate is almost zero at the point of contact "o" and gradually increases as we proceed towards the periphery of the lens. Thus, points where the thickness of air film is constant will lie on a circle with "o" as centre. That is why circular fringes are produced.
Question: 14
What are Newton's rings?
Answer: 14
14-35
When a plano-convex lens of long focal length is placed in contact with a plane glass plate, a thin air film is enclosed between them to form circular dark and bright fringes known as Newton's rings.
Question: 15
What is difference between interference and diffraction fringes?
Answer: 15
15-35
Interference Fringes: The superposition of two waves having same frequency and travelling in same direction results in bright and dark fringes is called interference fringes.

Diffraction Fringes: The fringes formed due to the bending of light around edges and corners are called diffraction fringes.
Question: 16
What is polarization of light?
Answer: 16
16-35
The phenomenon in which the vibration of waves can be oriented to any one direction, that may be vertical, horizontal, or any other direction is called polarization of light.
Question: 17
What is diffraction of light?
Answer: 17
17-35
The slight bending of light as it passes around the edge of an object is called diffraction of light.
Question: 18
In Newton's rings, Why are the fringes circular?
Answer: 18
18-35
The thickness of the air film between plano-convex lens and plane glass plate is almost zero at the point of contact "o" and gradually increases as we proceed towards the periphery of the lens. Thus, points where the thickness of air film is constant will lie on a circle with "o" as centre. That is why circular fringes are produced.
Question: 19
How would you manage to get more orders of spectra using a diffraction grating?
Answer: 19
19-35
Alternate Text
Question: 20
What is Michelson's interferometer? Also write its working principle.
Answer: 20
20-35
Michelson's interferometer is an instrument that is capable of measuring distance with extremely high precision.
Its working is based on interference. When light from a single source splits up into two parts and then interfere, it forms an interference pattern.
Question: 21
How would you distinguish between un-polarizedand plane polarized lights?
Answer: 21
21-35
Un-Polarized lights: A beam of ordinary light consists of electric and magnetic vibrations which are perpendicular to the direction of propagation. It is called un-polarized light.

Plane Polarized lights: The beam of light in which all vibrations are confined to one plane of vibration is called plane polarized light.
Question: 22
Why diffraction grating cannot be used for X-Rays diffraction?
Answer: 22
22-35
In order to observe the effects of diffraction, the grating spacing must be of the order of wavelength of the incident light.
X-rays are of much shorter wavelength of the order of 10-10 M
The regular array of atoms in a crystal forms a natural diffraction grating with spacing =10-10 M.Which is not available in other diffraction grating.
Question: 23
In Newton's rings, Why are the fringes circular?
Answer: 23
23-35
The thickness of the air film between plano-convex lens and plane glass plate is almost zero at the point of contact "o" and gradually increases as we proceed towards the periphery of the lens. Thus, points where the thickness of air film is constant will lie on a circle with "o" as centre. That is why circular fringes are produced.
Question: 24
What is the contribution of Michelson to measure the length of standard meter using interferometer?
Answer: 24
24-35
Michelson measured the length of the standard meter in terms of wavelength of red cadmium light and showed that the standard meter is equal to 1553163.5 wavelengths of this light.
Question: 25
Give the list of two substance which shows optical rotation when they are in solution.
Answer: 25
25-35
Sugar and tartaric acid show optical rotation when they are in solution.
Question: 26
Why the polaroid sun glasses are better than ordinary sun glasses?
Answer: 26
26-35
Polaroid sun glasses are better than ordinary sun glasses because they reduce the glare of light entering into the eye as a result of polarization.
Question: 27
Center of Newton ring is dark. Why? Although thickness of air film is zero.
Answer: 27
27-35
Alternate Text
Question: 28
What do you mean by coherent source ? Explain a common method for producing two coherent sources.
Answer: 28
28-35
The monochromatic sources of light which emit waves, having a constant phase difference are called coherent sources.
A common method of producing two coherent light beams is to use a monochromatic source to illuminate a screen containing two small holes, usually in the shape of slits. The light emerging from the two slits is coherent because a single source produces the original beam and two slits serve only too split it into two parts.
Question: 29
Can you obtain plane polarized light from un-polarized light? If your answer is yes, write the name of two processes by which plane polarized light is obtained.
Answer: 29
29-35
Yes , we can obtain plane polarized light from un-polarized light.
This can be achieved by processes such as
  • Selective absorption
  • Reflection from different surfaces
Question: 30
Define polarization of light.
Answer: 30
30-35
The phenomenon in which the vibration of waves can be oriented to any one direction (plane), That may be vertical, horizontal or any other direction is called polarization of light.
Question: 31
Write two uses of X-rays diffraction by crystals.
Answer: 31
31-35
X-ray diffraction has been very useful in determining the structure of biologically important molecules such as hemoglobin and double helix structure of DNA.
Question: 32
Write down selective absorption method to obtain plane polarized light from ordinary light.
Answer: 32
32-35
Selective Absorption: The selective absorption method is the most common method to obtain plane polarized light by using certain types of materials called dichroic substances. Theses materials transmit only those waves.Whose vibration are parallel to a particular direction and will absorb those waves vibrations are in other directions. One such commercial polarizing material is a polaroid.
Question: 33
What is the usual way to obtain plane wavefront from a point source?
Answer: 33
33-35
A usual way to obtain a plane wavefront is to place a point source of light at the focus of a convex lens. The rays coming out of the lens will constitute plane waves.
Question: 34
Define optical rotation. Give its practical use.
Answer: 34
34-35
When a plane polarized light is passed through certain crystals, they rotate the plane of polarization. It is called optical rotation.
Organic solutions such as sugar, tartaric acid etc., show optical rotation which is used to determine their concentration in the solutions.
Question: 35
Write the names of any four processes to obtain plane polarized beam of light from un-polarized light.
Answer: 35
35-35
This can be achieved by four processes such as
  1. Selective absorption
  2. Refraction throughout crystals
  3. Reflection from different surfaces
  4. Scattering by small particles.

11th Class Physics Chapters Short Questions