Q18 of 805 Page 1

What do you understand by the statement ‘Light from the sun is unpolarised’. Explain how does sunlight gets polarized by the process of scattering?

The light from the sun is unpolarized means that he electric field vectors vibrate in all possible directions in the transverse plane rapidly and randomly.


The polarization of sunlight by the method of scattering:


When the light from the sun enters the earth atmosphere it gets scattered by the molecules of gases in the earth atmosphere produces linearly polarized light in the plane perpendicular to the incident light. If the charges in a molecule are oscillating along the y-axis. Therefore at 90o away from beam direction, the scattered light is linearly polarized. The following diagram shows the polarization of blue light from the sky where the dots stands for polarization perpendicular in the plane of the figure. The double arrow shows the polarization in the plane of the figure.




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In a double slit experiment, the distance between the slits is 3 mm and the slits are 2 m away from the screen. Two interference patterns can be seen on the screen one due to light with wavelength 480 nm, and the other due to light with wavelength 600 nm. What is the separation on the screen between the fifth order bright fringes of the two interference patterns?

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Explain how does (i) photoelectric current and (ii) kinetic energy of the photoelectrons emitted in a photocell vary if the frequency of incident radiation is doubled, but keeping the intensity same? Show the graphical variation in the above two cases.

OR


(i) Name the experiment which confirms the existence of the wave nature of electrons. Derive the expression for the de-Broglie wavelength of an electron moving under a potential difference of V volts. (ii) An electron and a proton have the same Kinetic Energy. Which of these particles has a shorter de-Broglie wavelength?

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The energy levels of an atom of element X are shown in the diagram. Which one of the level transitions will result in the emission of photons of wavelength 620 nm? Support your answer with mathematical calculations.