11.Show that S.I. unit of illuminance lux is equal to lumen/meter2Â .
Illuminance is the luminous flux incident normally on unit area of the surface,
  E =  = Lumen/ m2Â
One lux is the illuminance on the inside of a sphere one metre at the centre of which a source of 1 C.P. is held.
Lux = Lumen/m2
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12.Light is incident on a block of glass at the polarizing angle. How does this polarising angle vary with the wavelength of light ?
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13.Fraunhoffer diffraction from a single slit of width 1.24 x 10-6Â m is observed with light of wavelength 6200 Ã…. Calculate the angular width of the central maximum
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14.Refractive index of the material of a concave lens is p. The lens is immersed in a medium of refractive index μ1 (μ1 > μ) . A parallel beam of light is incident on the lens. Draw a diagram to show the path of emergent rays.
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15.For an achromatic combination of lenses in contact, why should the lenses be of opposite nature ?
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16.An electron and a proton possess the same kinetic energy. Which of the two has greater de-Broglie wavelength ? Write down the formula used.
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17.How will you increase the penetrating power of X-rays produced in an X-ray tube ?
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18.The half-life of radon is 3.8 days. Calculate the amount of radon left undecayed in a sample containing 1024 mg of radon after 38 days.
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19.The energy of an electron in the first Bhor orbit of an atom is -27.2 eV. What will be the energy in the third orbit ?
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20.Explain why the electrical conductivity of a pure semiconductor increases on heating.
Short Answer Type
 = Lumen/ m2 
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