Dual Nature of Matter and Radiation 2 Flashcards
For a given metal and freqneucy, th
EXPLANATION BY EINSTEIN
Radiations absorbed by the surface are in the form of quanta (photon). Energy of each photon depends on
frequency.
One photon can interact with one electron at a time. In the interaction between photon and electron
incident photon transfers its whole energy to the electron.
If energy is sufficient then electron comes out without any time delay. It means photo electric effect is an
instantaneous process.
If intensity of the given source is increased then number of photon increases. So that, more number of electrons
are emitted and greater saturation current is obtained. It means saturation current depends upon intensity of the
given source is
µ I
5.4.3 At a time, only one photon can interact with one electron.
Energy of photon used by the electron is
hn = Kinetic energy of electron + Energy required to make electron free from the metal surface (f0
+ Energy lost in collision before emission (Q)
If Q = 0, means there is no heat loss, then kinetic energy of electron is maximum.
Now
hn = (K.E.max
(K.E.max) + f0) = hn – f0
Here n0 is threshold frequency for that V0
= 0
It means maximum K.E. and stopping potential (V0) depends on frequency. It is independent of intensity of the
given source.
KE is always more than 0
hn > hn0
n > n0
It means if frequency is less than ‘n ‘ , electron does not come ou
failure of wave theory
(i) According to wave theory when light incident on a surface, energy is distributed continuously over the
surface. So that electron must take a time interval to accumulate sufficient energy to come out. But in
experiment there is no time lag.
(ii) When intensity is increased, more energetic electrons should be emitted. So that stopping potential
should be intensity dependent. But it is not observed.
(iii) According to wave theory, if intensity is sufficient then, at each frequency, electron emission is possible. It
means there should not be existance of threshold frequency.
photon theory
(i) In interaction of radiation with matter, radiation behaves as if it is
made up of particles called photons.
(ii) Each photon has energy E (=hn) and momentum p (= h n/c), and
speed c, the speed of light.
(iii) All photons of light of a particular frequency n, or wavelength l, have
the same energy E (=hn = hc/l) and momentum p (= hn/c= h/l),
whatever the intensity of radiation may be. By increasing the intensity
of light of given wavelength, there is only an increase in the number of
photons per second crossing a given area, with each photon having
the same energy. Thus, photon energy is independent of intensity of
radiation.
(iv) Photons are electrically neutral and are not deflected by electric and
magnetic fields.
(v) In a photon-particle collision (such as photon-electron collision), the
total energy and total momentum are conserved. However, the number
of photons may not be conserved in a collision. The photon may be
absorbed or a new photon may be created.
DUAL NATURE OF LIGHT
Experimental phenomena of light reflection, refraction, interference, diffraction are explained only on the
basis of wave theory of light. These phenomena verify the wave nature of light.
Experimental phenomena of light photoelectric effect and Compton effect, pair production and pair annihilation
can be explained only on the basis of the particle nature of light. These phenomena verify the particle nature of
light.
It is inferred that light does not have any definite nature, rather its nature depends on its experimental
phenomenon. This is known as the dual nature of light. The wave nature and particle nature both can not be
possible simultaneously.
de broglie hypothesis
De Broglie imagined that as light possess both wave and particle nature, similarly matter must also posses both
nature, particle as well as wave.
De Broglie imagined that despite particle nature of matter, waves must also be associated with material particles.
Wave associated with material particles, are defined as matter waves.(the wavelength l of the matter wave is called de Broglie wavelength.)
He reasoned that nature was symmetrical and that the
two basic physical entities – matter and energy, must have
symmetrical character.
de broglie wavelength is applicable only to subatomic particles
This wavelength is so small that it is beyond any measurement. This
is the reason why macroscopic objects in our daily life do not show wavelike properties. On the other hand, in the sub-atomic domain, the wave
character of particles is significant and measurable.
