Optionals IAS Mains Physics: Questions 244 - 248 of 307

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Question 244

Appeared in Year: 2009

Describe in Detail

Essay▾

At what temperature are the rates of spontaneous and simulated emission become equal?

Explanation

If the rates of spontaneous and stimulated emission are equal, then

As

Question 245

Edit

Appeared in Year: 2011

Describe in Detail

Essay▾

Distinguish between intrinsic and extrinsic semiconductor. Show that in a semiconductor, the product of concentrations of the two types of charge carries is constant at a given temperature. (Marks 30)

Explanation

Pure or intrinsic semiconductors: The intrinsic semiconductors are pure semiconductors in which no impurity atoms are added. The intrinsic semiconductors such as pure or are undoped semiconductors. The electrical conductivity of this type of semiconductor is solely determined by thermally generated carriers. To understand the mechanism of conduct…

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Question 246

Dulong-Petit, Einstein, and Debye's Theories of Specific Heat of Solids

Appeared in Year: 2009

Describe in Detail

Essay▾

What are the limitations of Einstein՚s theory of specific heat of solids when compared with experiments at low temperature?

Outline the assumptions made in Debye՚s theory and show that the specific heat at low temperature follows law. What is the significance of Debye՚s temperature, ? (Marks 20)

Explanation

  • Although the Einstein՚s model provides a much better explanation for the variation of heat capacity with temperature than the Classical theory, it fails to account for the values of specific heat at very low temperatures. The Einstein՚s theory assumed that the atoms of a crystal vibrate totally independent of each other.
  • The vibrational motion of th…

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Question 247

Production and Detection of Linearly and Circularly Polarised Light

Appeared in Year: 2009

Describe in Detail

Essay▾

A plane polarized light is incident perpendicularly on a quartz plate cut with faces parallel to the optic axis. Find the thickness of the quartz plate which introduces phase difference of between

Explanation

The path difference between the waves is given by,

The phase difference between the waves is given by,

Question 248

Fraunhofer Diffraction-Single Slit, Double Slit, Diffraction Grating, Resolving Power
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Appeared in Year: 2009

Describe in Detail

Essay▾

Distinguish between high dispersive power and high resolving power. (Marks - 5)

Explanation

  • The dispersive power of a grating is given by and the resolving power is given by where n is the order of the spectrum and N is the total number of lines on the grating surface. N′ is the number of lines per cm on the grating surface. Here ives the direction of the principle maximum corresponding to a wavelength .
  • From the above equation, it is …

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