11.Can two sodium vapour lamps.act as coherent sources? Explain in brief.
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12.Why all over the world, giant telescopes are of reflecting type? State any one reason.
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13.A ray of ordinary light is incident on a rectangular block of glass at Brewster’s angle. What is the angle between the reflected ray and the refracted ray of light?
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14.Find the momentum of a photon of energy 3.0 eV.
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15.The half life of a certain radio active element is 8 hours. If a pupil starts with 32 g of this element, how much of the sample will be left behind at the end of one day?
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16.If a hydrogen atom goes from III excited state to II excited state, what kind of radiation (visible light, ultra violet, infra red, etc.) is emitted?
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17.Where in our universe is the thermo-nuclear energy being released naturally?
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18.In which of the solids (semi-conductors, conductors or insulators) do conduction band and valence band overlap?