12.Why all over the world, giant telescopes are of reflecting type? State any one reason.
The construction and grindling of large lenses is very difficult.
To overcome this difficulty concave (reflecting type) mirrors are used.
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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?
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19.What is the symbol of a NOR gate?
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20.Find the electric charge Q1 on plates of capacitor C1, shown in Figure 3 below:
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