Thank you for registering.

One of our academic counsellors will contact you within 1 working day.

Please check your email for login details.
MY CART (5)

Use Coupon: CART20 and get 20% off on all online Study Material

ITEM
DETAILS
MRP
DISCOUNT
FINAL PRICE
Total Price: Rs.

There are no items in this cart.
Continue Shopping

electromagnetic radiation quantum theory of radiation

electromagnetic radiation


quantum theory of radiation

Grade:11

2 Answers

bhaveen kumar
38 Points
8 years ago

Electromagnetic radiation (EM radiation or EMR) is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space. EMR has both electric and magnetic field components, which stand in a fixed ratio of intensity to each other, and which oscillate in phase perpendicular to each other and perpendicular to the direction of energy and wave propagation. In a vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.

Electromagnetic radiation is a particular form of the more general electromagnetic field (EM field), which is produced by moving charges. Electromagnetic radiation is associated with EM fields that are far enough away from the moving charges that produced them that absorption of the EM radiation no longer affects the behavior of these moving charges. These two types or behaviors of EM field are sometimes referred to as the near and far field. In this language, EMR is merely another name for the far-field. Charges and currents directly produce the near-field. However, charges and currents produce EMR only indirectly—rather, in EMR, both the magnetic and electric fields are associated with changes in the other type of field, not directly by charges and currents. This close relationship assures that the electric and magnetic fields in EMR exist in a constant ratio of strengths to each other, and also to be found in phase, with maxima and nodes in each found at the same places in space.

 

 

 

Aravind Bommera
36 Points
8 years ago

Electromagnetic radiation (EM radiation or EMR) is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space. EMR has both electric and magnetic field components, which stand in a fixed ratio of intensity to each other, and which oscillate in phase perpendicular to each other and perpendicular to the direction of energy and wave propagation. In a vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.

Electromagnetic radiation is a particular form of the more general electromagnetic field (EM field), which is produced by moving charges. Electromagnetic radiation is associated with EM fields that are far enough away from the moving charges that produced them that absorption of the EM radiation no longer affects the behavior of these moving charges. These two types or behaviors of EM field are sometimes referred to as the near and far field. In this language, EMR is merely another name for the far-field. Charges and currents directly produce the near-field. However, charges and currents produce EMR only indirectly—rather, in EMR, both the magnetic and electric fields are associated with changes in the other type of field, not directly by charges and currents. This close relationship assures that the electric and magnetic fields in EMR exist in a constant ratio of strengths to each other, and also to be found in phase, with maxima and nodes in each found at the same places in space.

EMR carries energy—sometimes called radiant energy—through space continuously away from the source (this is not true of the near-field part of the EM field). EMR also carries both momentum and angular momentum. These properties may all be imparted to matter with which it interacts. EMR is produced from other types of energy when created, and it is converted to other types of energy when it is destroyed. The photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR. The quantum nature of light becomes more apparent at high frequencies (or high photon energy). Such photons behave more like particles than lower-frequency photons do.

In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them. Electrons are responsible for emission of most EMR because they have low mass, and therefore are easily accelerated by a variety of mechanisms. Rapidly moving electrons are most sharply accelerated when they encounter a region of force, so they are responsible for producing much of the highest frequency electromagnetic radiation observed in nature. Quantum processes can also produce EMR, such as when atomic nuclei undergo gamma decay, and processes such as neutral pion decay.

EMR is classified according to the frequency of its wave. The electromagnetic spectrum, in order of increasing frequency and decreasing wavelength, consists of radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. The eyes of various organisms sense a small and somewhat variable but relatively small range of frequencies of EMR called the visible spectrum or light.

The effects of EMR upon biological systems (and also to many other chemical systems, under standard conditions) depends both upon the radiation''s power and frequency. For lower frequencies of EMR up to those of visible light (i.e., radio, microwave, infrared), the damage done to cells and also to many ordinary materials under such conditions is determined mainly by heating effects, and thus by the radiation power. By contrast, for higher frequency radiations at ultraviolet frequencies and above (i.e., X-rays and gamma rays) the damage to chemical materials and living cells by EMR is far larger than that done by simple heating, due to the ability of single photons in such high frequency EMR to damage individual molecules chemically.

 

 

THE QUANTUM THEORY OF RADIATION
To understand how an atom interacts with the electromagnetic field and finally how one
atom interacts with another, we need to discuss the field in relationship to its sources. It
is convenient to begin with the classical descriptions and then move to the quantum
mechanical viewpoint from which the field is seen it its own right as a quantum system
that can exchange energy with atoms.
There is a parallel between the oscillating, macroscopic currents found in antennas and
the time-varying probability density for the electron in an excited atom. Considering the
electromagnetic environment, there is a parallel between the vector of the macroscopic
electric field and the probability amplitude for photons in a field of any strength.

The classical Maxwell equations describe how the periodic motion of a macroscopic
electric charge (for example as with a current oscillating in a linear antenna) produces
the electric and magnetic vectors of the radiation field. An individual atom can be
influenced by the field, but the effect of the atom on the field is not clearly set forth.
In the quantum view, by contrast, the electromagnetic field itself is regarded as a
system that can be described in terms of excitation of its normal modes, the occupation
numbers for which describe the excited states of the system. The atom is also a system
with normal modes, and atom-field coupling leads both the field and the atom to undergo
transitions. We find that the quantum description, when used to express the expectation
from a highly excited field coupled to many atoms, blends smoothly with the classical
description.

 

 

Want more information go to http://www.google.co.in/url?q=http://www-personal.umich.edu/~jenszorn/1JZPhysTeach/453F95%2520QM%2520Text%25201-2%2520copy/808_QM_TheoRad_F95.pdf&sa=U&ei=804aUbDULYnprAf09IHABw&ved=0CDIQFjAF&usg=AFQjCNGiYOIaArYGvzfClxZITkNh2qTRgg

Think You Can Provide A Better Answer ?

Provide a better Answer & Earn Cool Goodies See our forum point policy

ASK QUESTION

Get your questions answered by the expert for free