PhotoElectric Effect - Physics Notes - Engineering Diploma by ednexa.com

1. Photo Electric Effect
Electrons are present on the surface of conductor. These electrons are
loosely bounded with the nucleus. In few metals these electrons are
released from its surface when the metal is expose to light. This effect is
known as photo electric effect.
“Phenomenon of emission of electrons by metal surface under the action of
light is called as photo-electric effect. The emitted electrons in this process
are called as photo-electrons.” Alkali metals like sodium, potassium shows
this effect.

2. 1.
Frequency of incident radiation.
1.
Initially P.D. & intensity of radiation are kept constant.
It is observed that, at low frequency, photo-electric current
cannot flow.
This
certain
minimum
frequency
at
and
above
which
photoelectric current starts is called as threshold frequency ( 0
).
Threshold frequency is differs for different metals. Wavelength
of light corresponding to threshold frequency is called as
threshold wavelength (λ0)

3. 2.
Now, frequency (greater than threshold frequency) & potential
difference are kept constant. It is observed that photoelectric
current increases as intensity of incident radiation increases.
Photoelectric current is directly proportional to intensity of
incident radiations.

4. 3.
Now frequency (greater than threshold frequency) & intensity
incident radiation are kept constant

5. It is observed the photo-electric current stops at certain -ve
potential. This value of potential is called as stopping potential
(Vs).
It is also observed that value of stopping potential increases as
the frequency of incident radiation increases.
The relation between kinetic energy (K.E.) and stopping
potential (Vs) is K.E.=Vs.e

6. 4.
As soon as light radiation incident on photo sensitive material,
electron emission starts and current flows. That means
photoelectric effect is an instantaneous process.
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