Photoelectric effect
The
phenomenon is discovered by Heinrich Hertz .
who was
a German physicist.
When
a beam of radiation of a certain frequency falls on the metal surface, the
electrons are emitted from the metal surface
Is
a phenomenon of instant ejection of the electron from a metal when the light of
particular frequency/wavelength is incident on the metal surface
Parameter
1. Frequency of light (color of light)
2. Intensity of light (brightness)
·
Frequency
effect
When we use low
frequency number electron ejected from the metal surface when we increase the
frequency of light slowly after a certain value of frequency the electrons
start ejecting from the surface of the metal and when be further increase the
velocity of the electron the velocity of ejected electron increases.
The particular value of
frequency, when the electron start ejecting from the metal surface,
Or
The minimum amount of
frequency required to remove the electron from the surface of the metal is
called threshold frequency
λ=c/ ν0
λ is threshold wavelength
·
Intensity
we
choose the frequency above the threshold frequency .we absorbed that when we
increase the intensity of the light the number of electrons ejected
increase and with decreasing intensity the number of electron
ejected decreases there is one effect on the velocity of the ejected electron.
·
Summary
· For photoelectric emission we
required a minimum amount of frequency/wavelength is required is called
threshold frequency or threshold wavelength.
· When we increase the
frequency of light the speed of ejected electron increase that is the kinetic
energy of ejected electron increases (Photocurrent remain same)
· When we increase the intensity of the light the number of electron ejected increase that is
photocurrent increases (Kinetic Energy remain same of the ejected electron)
Einstein’s Theory
of Photoelectric Effect using Quantum Theory
Einstein gives a successful explanation
of Photoelectric effect.
Einstein made three simple Postulate
·
Light is made up
of photons with energy (E = hν ) (where h is plank’s
constant and ν is the frequency of light radiation)
·
Each photon can eject only one electron
·
Give a simple governing equation of the photoelectric effect
hν
= hvo +1/2 mv2
where
· hν is the energy of the Photon
· hvo is called Work function it is also
denoted by ɸ (
vo is the threshold frequency)
·1/2 mv2 is the kinetic energy of the ejected electron
Einstein use
planck’s quantum theory to give an explanation
of the photoelectric effect. According to the Planck’s theory, the light is made
up of the discrete packets of the energy called a Photon. Each photon has energy
equal to hν (where h is plank’s constant and ν is the
frequency of light radiation) when photon of frequency ν strike with the electron
in a metal its transfer its energy hν to the electron
The energy is use in two ways
·
some part of the energy is used to overcome the threshold energy
barrier of the metal ( is called work function )
·
and the remaining energy is converted into the kinetic energy of
the ejected electron
hν
= hvo + 1/2mv2
hν
= hvo + K.E.
that is K.E = hν- hvo
this equation
show that The kinetic energy of the electron depends upon the frequency of the
incident light and not on its intensity i.e. when the intensity of light is increased
the number of photons striking the metal surface per unit time increases. thus
more number of electrons will be emitted, however, the kinetic energy remains unaffected.
Is defined
as the value of the reverse voltage applied where
the velocity of electron becomes zero is called stopping potential v0
Photoelectric effect
Reviewed by Nitesh Singh
on
October 11, 2019
Rating:
Reviewed by Nitesh Singh
on
October 11, 2019
Rating:
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