Electromagnetic Theory & Black Body Radiation [IFS (Forest Services) Physics]: Questions 1 - 7 of 28

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Question 1

Appeared in Year: 2015 (IAS)

Describe in Detail Subjective▾

Derive the equation that represents Poynting՚s theorem. What is its physical significance? (20 Marks)

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Explanation

  • We know that

    Electromagnetic potential energy … eq. (1)

    Energy stored in a magnetic field … eq. (2)

  • Maxwell՚s e…

… (1047 more equations) …

Question 2

Appeared in Year: 2015 (IAS)

Describe in Detail Subjective▾

Show that the differential scattering cross section can be expressed as

Where s is the impact parameter and is the scattering angle. (15 Marks)

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Explanation

  • Let us consider a uniform beam of particles all of the same mass and kinetic energy, incident upon the centre of force. The incident beam is characterized by specifying its intensity I, defined as the number of particles crossing unit area normal to the beam in unit time.
  • When the experiment is performed with many particles simultaneously, then inst…

… (104 more equations, 7 figures) …

Question 3

Appeared in Year: 2015 (IAS)

Write in Short Short Answer▾

Establish that:

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Question 4

Appeared in Year: 2009 (IAS)

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Using Planck՚s radiation formula, deduce Wein՚s displacement law. (10 Marks)

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Explanation

  • Planck՚s formula is given by

  • Differentiating it partially with respect to , we get

… (76 more equations) …

Question 5

Appeared in Year: 2004 (IAS)

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What do you understand by a perfect black body? Can it be realized in practice? Show that the ratio of emissive power to the absorptive power of all bodies at a given temperature is equal to the emissive power of a perfectly black body.

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Explanation

A perfectly black body is one which absorbs all the heat radiations of whatever wavelength incident on it.

It neither reflects nor transmits any of the incident radiation and therefore appears black whatever the colour of incident radiation be.

Let a black body be placed in an isothermal enclosure. The body will emit the full radiations of the enclos…

… (219 more equations, 5 figures) …

Question 6

Appeared in Year: 2004 (IAS)

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Show that the Poynting vector represents the energy flow per unit area per unit time both in magnitude and direction in case of a plane electromagnetic wave.

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Explanation

Electromagnetic potential energy

And energy stored in a magnetic field

… (1874 more equations) …

Question 7

Appeared in Year: 2004 (IAS)

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What are the vector and scalar potential? Drive Maxwell՚s wave Equations in terms of these potentials

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Explanation

Maxwell field equations are:

… (567 more equations) …