Christensen physics

1. STRUCTURE OF ATOM
AND
ELECTROMAGNETIC
SPECTRUM

2.  In 1897, J.J. Thompson discovered a negatively
charged particle much smaller than any atom which
came to be known as electron.
 Based on the work of Rutherford & Bohr,a simple
model of an atom may be visualised as a massive
positively charged nucleus surrounded by electrons
in orbits of specific diameters.
Structure of atom is organised on similar fashion as
the solar system.

3. Structure of atom

5. Structure of atom is organised as nucleus at the
centre surrounded by electrons in their respective
orbits.
Most of the atom is empty space. Diameter of atom
is 100,000 times larger than diameter of its nucleus.
NUCLEUS:
Nucleus of atom is made up of several types of
elementary particles termed nucleolus.
 Of the nucleolus the important ones are protons
and neutrons.
PROTON : Has positive charge numerically equal to
charge of electron.
NEUTRON: Has zero charge.

6. Neutron and proton have about same
mass,which is approximately 1836 times greater
than the mass of electron.
ATOMIC NUMBER: ( Z )
Number of protons in the nucleus.
MASS NUMBER : ( A )
Total number of protons and neutrons in the
nucleus of atom.
All atoms of an element have same atomic no but
may have several isotopes.
All isotopes have same atomic no but differ in
mass number as number of neutrons vary.

7. ELECTRONORBITSANDENERGYLEVELS
Atom is electrically neutral as it has equal
number of electrons and protons.
 Negatively charged electrons revolve around the
nucleus in circular orbits.
The atomic system allows 2 electrons in 1st orbit,
8 in 2nd, upto 18 in 3rd, 32 in 4th, 50 in 5th.
 Electron orbits are designated by letters
K,L,M,N,O and so on.

8. Attractive force between positively charged
nucleus and negatively charged electrons is force
that keeps electrons in the orbit. This force is
called as BINDING FORCE of the electron.
The binding force is inversely proportional to the
square of distance between nucleus and electron.
So K electron has larger binding force than L
electron.
This force keeps electrons moving in a circular
path around nucleus.

9. BINDING ENERGY:
To free an electron from an atom, energy must be
raised to zero/positive value . The energy the
electron in a shell must be given to raise value to
zero is called Binding energy.
The binding energy differs from one element to
other , as atomic no increases binding energy
increases.

11. An atom is said to be ionized when on of its
electron has been completely removed
 Electrons may jump from one energy shell to
another if the shell to which it jumps not already
filled.
An atom is said to be excited when an electron is
raised from one shell to another.

12. When an electron is raised to higher energy shell,
expenditure of energy occurs.
Similarly when an electron movement occurs to a
lower energy shell, emission of energy occurs.
This energy may take form of a photon.
If the quantity of energy is sufficient, the photon
may be called an X ray.

13. DIAGNOSTIC IMPORTANCE:
The production of x rays makes use of three
properties of tungsten atoms in the target of x ray
tube: 1.Electric field of nucleus.
2.Binding energy of orbital electrons.
3.Need of an atom to exist in lowest energy
state.

14. Electro magnetic
spectrum

15. Electro magnetic radiation is the transport of
energy through space as a combination of electric
and magnetic fields.
Electromagnetic radiation is produced by a
charged particle being accelerated.
The electric and magnetic field components
oscillate in phase perpendicular to each other and
perpendicular to the direction of energy
production.

16. EM radiation travel through empty space as well
as through air and other substances.
EM radiation carries energy and momentum that
may be imparted to matter which it interacts.
EM has dual personality.Besides acting like
waves,it acts like stream of particles(called as
photons) that have no mass.

18. A positive charge at rest is surrounded by electric
and magnetic fields.
If a charge moves with constant velocity, we not
only see electric field moving but also a magnetic
field surrounding the line along which the
charge moving.
When a charge acclerates,the charge moves to a
new location but the electric field lags behind as
does the magnetic field.

19. The lagging behind produces a kink in the
electric field lines that moves outward from the
charge with a finite(but large) velocity.
 We can think this kink being known as EM
radiation.
The concept is that E and M field interact to
build each other upto some value,then collapse
together and build each other up in the opposite
direction.
 This energy is transmitted through space by the
EM radiation.

20. Wave concept
EM radiation is propagated through space in the
form of waves.
Waves of all types have associated wavelength and
frequency.
WAVELENGTH ( λ ): Distance between two
successive crests or troughs.
FREQUENCY (ν) : Number of waves passing a
particular point in unit time.
VELOCITY (V) : Distance travelled per second by a
point .
V= ν x λ

21.  EM radiation always travels at the same velocity
in a vaccum,which is equal to velocity of light.
c= ν x λ
 All EM radiations have same velocity so,the
frequency of radiation must be inversely
proportional to wavelength.
 So all types of radiation in electromagnetic
spectrum differ only in wavelength.


22. Wavelength
• Radio,television,radar : 3x106 to 1cm.
• Infrared radiation : 0.01 to 0.00008 cm
• Visible light : 7500(0.000075)to 3900 Å
• Ultraviolet : 3900 to 20 Å
• Soft x rays : 100 to 1 Å
• Diagnostic x rays : 1 to 0.1Å
• Therapeutic x rays : 0.1 to 104 Å
And gamma rays

23. Particle concept
EM waves may react with matter as if they were
particles rather than waves.
These particles are discrete bundles of energy
called as Quantum or Photon.
The amount of energy(E) carried by each photon
depends on frequency of the radiation.
If the frequency is doubled , energy is doubled.
E=hx ν
E= Energy of photon
h= Plancks constant i.e 4.13x10-18 keV.
ν= Frequency

24. Classification of EM spectrum
• Gamma radiation
• X-ray radiation
• Ultraviolet radiation
• Visible radiation
• Infrared radiation
• Terahertz radiation
• Microwave radiation
• Radio waves
• This classification goes in increasing order of
wavelength.( in other words decreasing order of
frequencies).

25. EM Spectrum

27.  The EM spectrum further classified into Ionizing and
non ionizing radiation.
 Ionizing radiation is radiation that carries enough
energy to free electrons from atoms or molecules,
thereby ionizing them.
 ex: x rays, gamma rays, some part of uv rays
 Non-ionizing radiation is radiation that does not
carry enough energy , to completely remove an
electron from an atom.
 ex: Visible radiation, infrared radiation, low-energy
radio waves and microwaves
 Ionising radiation has more energy than non
ionising radiation; enough to cause chemical
changes by breaking chemical bonds.

28. COMMON PROPERTIES OF EMR
 It travels through free space as straight lines
 The speed of EMR is constant in space. All forms of
EMR have the same speed of 299,800
kilometers/second (~ 3 x 108 m/s) in space
 According to quantum theory of EMR, the energy
associated with a photon is given as
E = hυ where , E= Photon energy, h=
Planck’s constant , u= frequency.
 Electromagnetic radiation on passing through a
medium gets attenuated
 EMR obeys Inverse square law

29. Inverse Square Law
 The intensity of the radiation from a point source
varies inversely as the square of the distance
from the source, provided there is no absorption
(or) scattering by the medium.

30. THANK YOU