# Wave Optics -Important Questions & Preparation Tips

In this article you will get the clue that from where and how the questions are being framed from chapter Wave Optics

Created On: Sep 25, 2013 18:10 IST
Modified On: Dec 28, 2015 15:03 IST

CBSE Class 12th Chapter, Wave Optics comes under the topic Optics which carries 14 Marks in board exam. Experts of Jagranjosh.com offer the best practice material that covers all important questions so that students will not miss any portion while preparing for board exams or competitive exams. Consider the mentioned terms/questions at the time of studying.

• What was the basic idea suggested by the corpuscular theory of Newton? What was its backdrop?
• With an example prove that light travels in straight line?
• State Huygens’s principle. Explain with the help of a diagram, the phenomenon of refraction of waves on the basis of this principle?
• A light pulse is sent through a medium. Will it retain its shape?
• Why is the contribution of the wavelets lying on the back of the wave front zero?
• What determines the intensity of light in the photon picture of light?
• For the same angle of incidence, the angle of refraction in three different media A, B and C are 150, 250 and 350 respectively. Find the medium having least speed of light?
• Explain the statement ‘Light added to light can produce darkness.’
• Does energy conservation hold in interference?
• Can two independent sources of light be coherent?
• When a low-flying aircraft passes overhead, we notice a slight shaking of the picture on our TV screen. Why?
• Why is no interference pattern observed when two coherent sources are:

a) Infinitely close to each other

b) Far apart from each other

• Describe young’s experiment of interference of light. Obtain the conditions of maxima and minima of light?
• Two waves of equal frequencies have their amplitudes in the ratio of 3:5. They are superimposed on each other. Calculate the ratio of maximum and minimum intensities of the resultant wave?
• In young’s experiment, the wavelength of light used is 6000 Å, the distance between two slits is 0.05 cm and the distance of screen from the slits is 1m. Find out the distance between first dark fringe and first bright fringe?
• What is the basic difference between interference and diffraction of light?

• Why is diffraction not observed when a wide slit is illuminated by monochromatic light?
• Colored spectrum is seen when we look through a muslin cloth, but not through coarse cloth. Why?
• How is diffraction effect suppressed in young’s double slit experiment?
• Radio waves diffract strongly around buildings, but light waves, which are also electromagnetic waves, do not. Why?
• Why is diffraction common in sound but not in light?
• Obtain the relation a sin ɵ = λ for the first minimum of the diffraction pattern of a single slit of width a using light of wavelength λ.
• Light waves can be polarized while sound waves cannot be. Why?
• State Brewster’s Law of polarization?
• Why are sunglasses made of Polaroid preferred more over colored glass? Explain the phenomenon in detail.
• State and explain the Law of Malus?
• How does an unpolarized light incident on a Polaroid get polarized?

a) Described briefly, with help of a necessary diagram, the polarization of light by reflection from a transparent medium.

b) Two Polaroid’s ‘A’ and ‘B’ are kept in crossed position. How should a third Polaroid ‘C’ be placed between them so that the intensity of polarized light        transmitted by Polaroid B reduces to 1/8th of the intensity of unpolarized light incident on A ?

• (a) In Young's double slit experiment, derive the condition for (i) constructive interference and (ii) destructive interference at a point on the screen.

(b) A beam of light consisting of two wavelengths, 800 nm and 600 nm is used to obtain the interference fringes in a Young's double slit experiment on a screen placed 1.4 m away. If the two slits are separated by 0.28 mm, calculate the least distance from the central bright maximum where the bright fringes of the two wavelengths coincide.

• What is linearly polarised light? Describe briefly using a diagram how sunlight is polarised.

• Unpolarised light is incident on a Polaroid. How the intensity of would transmitted light change when the Polaroid is rotated?
• Use Huygens’s principle to explain the formation of diffraction pattern due to a single slit illuminated by a monochromatic source of light.
When the width of the slit is made double the original width, how would this affect the size and intensity of the central diffraction band?
• (a) Why are coherent sources necessary to produce a sustained interference pattern?
(b) In Young’s double slit experiment using monochromatic light of wavelength  the intensity of light at a point on the screen where path difference is , is K units. Find out the intensity of light at a point where path difference is /3.

• Use Huygens’ geometrical construction to show the propagation of a plane wave front from a rarer medium (1) to a denser medium (2) undergoing refraction.
Hence derive Snell’s law of refraction.
• In deriving the single slit diffraction pattern, it was stated that the intensity is zero at angles of nλ/a. Justify this by suitably dividing the slit to bring out the cancellation.
• Differentiate between the red shift and the blue shift?
• What speed should a galaxy move with respect to us so that the sodium line at 589.0 nm is observed at 589.9 nm?

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