﻿ Describe the absorption spectrum of Sodium. from Class 12 ISC P

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## ISC Class 12 Physics Solved Question Paper 2009

#### Short Answer Type

1. Explain the statement ‘Relative permittivity of water is 81’
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2. Draw (at least three) electric lines of force due to an electric dipole.
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3. Find the value of resistance X in the circuit below so that the junctions M and N are at the same potential:
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4. When the cold junction of a certain thermo-couple was maintained at 20°C, its neutral temperature was found to be 180°C. Find its temperature of inversion.
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5. State how the magnetic susceptibility of a ferromagnetic material changes when it is heated.
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6. What is the value of power factor in a series LCR circuit at resonance?
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7. An a.c. generator generates an emf ‘e’ given by: e = 311 Sin (100 πt) volt. Find the rms value of the emf generated by the generator.
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8. A ray LM of monochromatic light incident normally on one refracting surface AB of a regular glass prism ABC emerges in air from the adjacent surface AC as shown in Figure 2. Calculate the refractive index of the material of the prism.
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# 9.Describe the absorption spectrum of Sodium.

The missing wavelengths are identified as the dark lines in the spectrum. Such a spectrum is called an absorption spectrum.

The missing wavelengths (i.e. dark lines in the spectrum) have been absorbed by the sodium vapour because the light of these wavelengths is exactly of the right energy to cause electron transitions within the sodium atoms.

Therefore, find that dark lines in the absorption spectrum of sodium occur at the same position as the bright lines in the emission spectrum of sodium as shown in fig. below.

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10. A thin converging lens of focal length 15 cm is kept in contact with a thin diverging lens of focal length 20 cm. Find the focal length of this combination.
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