Ans. Two or more waves having a constant phase difference (same λ & T) are called coherent sources. One method of producing two coherent light beams is to use monochromatic source to illuminate a two holes screen. The light emerging from the two slits is coherent because a single source produces two parts.
Q.2 How is the distance between interference fringes affected by the separation between
the slits of Young’s experiment? Can fringes disappear?
Ans. We have Fringe spacing = ∆y = λL / d The relation shows that fringe spacing is inversely proportional to the separation ‘d’ between the slits. If separation is increased the distance between fringes will decrease. Ultimately fringes disappear for larger distance between the slits.
Q.3 Can visible light produce interference fringes? Explain.
Ans. Yes. Visible light can produce interference fringes, if it has phase coherence. White light will produce coloured interference fringes.
Q.4 In the Young’s experiment, one of the slits is covered with blue filter and other with red filter. What would be the pattern of light intensity on the screen?
Ans. No interference pattern will be observed as blue and red light not being in phase coherence.
Q.5 Explain whether the Young’s experiment is an experiment for studying interference or diffraction effects of light.
Ans. Diffraction is a special type of interference. Young’s experiment primarily is for studying interference. But diffraction is accompanied. Light is diffracted from two slits. So it is a combination of diffraction and interference.
Q.6 An oil film spreading over a wet footpath shows colours. Explain how does it
happen?
Ans. Due to interference of light waves, colours are seen on the oil film. At a certain place of the film, its thickness and the angle of incidence of light are such that the condition of destructive interference of one colour is being satisfied. Hence that portion of the film will exhibit the remaining constituent colours of the white light.
Q.7 Could you obtain Newton’s rings with transmitted light? If yeas, would the pattern be different from that obtained with reflected light?
Ans. Yes. We can obtain Newton’s rings with transmitted light. the difference will be that, the central spot will be bright.
Q.8 In the white light spectrum obtained with a diffraction grating, the third order image of a wavelength coincides with the fourth order image of a second wavelength. Calculate the ratio of the two wavelengths.
Ans. d sinθ = nλ ; d sinθ = 3λ1 , & d sinθ = 4λ2 ⇒ 3λ1 = 4λ2 or λ1/ λ2 = 4/3
Q.9 How would you manage to get more orders of spectra using a diffraction grating?
Ans. We have, d sinθ = nλ To increase more orders of spectra (n), we should increase the grating element (d), i.e. a grating with lesser number of ruled lines.
Q.10 Why the Polaroid sunglasses are better than ordinary sunglasses?
Ans. Polaroid sunglasses reduces glare, as they produce plane polarized light.
Q.11 How would you distinguish between un-polarized and plan-polarized lights?
Ans. A Polaroid will distinguish between un-polarized and plane-polarized light. If a Polaroid is rotated in front of un-polarized light, a component of light will pass for each angle. But for plane-polarized light, at certain orientation, no light will pass.
Q.12 Fill the blanks.
i) According to _________ principle, each point on a wave front acts as a source of
secondary _______.
ii) In Young’s experiment, the distance between two adjacent bright fringes for violet
light is _______ than that fore green light.
iii) The distance between bright fringes in the interference pattern______ as the
wavelength of light used increases.
iv) A diffraction grating is used to make a diffraction pattern for yellow light and
then for red light. The distances between the red spots will be_____ than that for
yellow light.
v) The phenomenon of polarization of light reveals that light waves
are______ waves.
vi) A Polaroid glass_______ glare of light produced at a road surface.
Ans. i) Huygen’s , wavelets ii) smaller iii) increases iv) larger, v) transverse vi) polarizing material, vii) reduce.
not best if its notes topic vise so.....
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