Today we will see how to make project on 'Project on photoelectric effect for class 12th' this project is only for class 12th student and this project is belongs to 'DUAL NATURE OF RADIATION AND MATTER' in this project we will cover following steps
1. Photoelectric Effect
2. Experimental Set-up to study
Photoelectric Effect
3. Laws of Photoelectric Effect
4. Einstein’s Photoelectric Equation
5. Verification of Laws of Photoelectric
Effect based on Einstein’s
Photoelectric Effect:
The phenomenon of emission of electrons from mainly
metal surfaces exposed to light energy (X – rays, γ – rays, UV rays, visible light and even Infra Red rays) of suitable frequency is known as photoelectric effect.
1.The electrons emitted by this effect are called photoelectrons.
2.The current constituted by photoelectrons is known as photoelectric current.
3.Non metals also show photoelectric effect. Liquids and
gases also show this effect but to limited extent.
►Each metal has a minimum energy needed for an electron to be emitted.
► This is known as the work function, W.
► So, for an electron to be emitted, the energy of the photon, hf,
must be greater than the work function, W.
► The excess energy is the kinetic energy, E of the emitted
electron.
Experimental Set-up to study Photoelectric Effect
1.Glass transmits only visible and infra-red lights but not UV light. Quartz transmits UV light.
2.When light of suitable frequency falls on the metallic cathode, photoelectrons are emitted.
3.These photoelectrons are attracted towards the +ve anode and hence photoelectric current is constituted.
1) Effect of Intensity of Incident Light on Photoelectric
Current:
For a fixed frequency, the photoelectric current increases
linearly with increase in intensity of incident light.
2) Effect of Potential on Photoelectric Current:
For a fixed frequency and intensity of incident light, the
photoelectric current increases with increase in +ve
potential applied to the anode.
♦️ When all the photoelectrons reach the plate A,
current becomes maximum and is known as
saturation current.
♦️ Photoelectrons manage to reach the plate on their
own due or cut-off of incident light does not affect
the stopping potential
♦️ When the potential is decreased, the current
decreases but does not become zero at zero potential.
♦️ When –ve potential is applied to the plate A w.r.t. C,
photoelectric current becomes zero at a particular
value of –ve potential called stopping potential.
3) Effect of Frequency of Incident Light on Photoelectric
current:-
For a fixed intensity of incident light, the photoelectric
current does not depend on the frequency of the incident
light. Because the photoelectric current simply depends
on the number of photoelectrons emitted and in turn on
the number of photons incident and not on the energy of
photons.
4) Effect of Frequency of Incident Light on Stopping
Potential:
♦️ For a fixed intensity of incident light, the
photoelectric current increases and is saturated with
increase in +ve potential applied to the anode.
♦️However, the saturation current is same for different
frequencies of the incident lights.
♦️ When potential is decreased and taken below zero,
photoelectric current decreases to zero but at different
stopping potentials for different frequencies.
♦️ Higher the frequency, higher the stopping potential
i.e. VS α ν.
5) Threshold Frequency:
The graph between stopping potential and frequency does
not pass through the origin. It shows that there is a
minimum value of frequency called threshold frequency
below which photoelectric emission is not possible
however high the intensity of incident light may be. It
depends on the nature of the metal emitting
photoelectrons.
Laws of Photoelectric Emission
♦️For a given substance, there is a minimum value of frequency of incident light called threshold frequency below which no photoelectric emission is possible, howsoever, the intensity of incident light may be.
♦️The number of photoelectrons emitted per second (i.e. photoelectric current) is directly proportional to the intensity of incident light provided the frequency is above the threshold frequency.
♦️The maximum kinetic energy of the photoelectrons is directly proportional to the frequency provided the frequency is above the threshold frequency.
♦️The maximum kinetic energy of the photoelectrons is independent of the intensity of the incident light.
♦️The process of photoelectric emission is instantaneous. i.e. as soon as the photon of suitable frequency falls on the substance, it emits photoelectrons.
♦️The photoelectric emission is one-to-one. i.e. for every photon of suitable frequency one electron is emitted.
Einstein’s Photoelectric Equation
◼️When a photon of energy hν falls on a metal surface,
the energy of the photon is absorbed by the electron
and is used in two ways:
1. A part of energy is used to overcome the surface barrier
and come out of the metal surface. This part of the energy
is called ‘work function’(Ф = hν0).
2. The remaining part of the energy is used in giving a
velocity ‘v’ to the emitted photoelectron. This is equal to
the maximum kinetic energy of the photoelectrons ( ½
mv2max ) where ‘m’ is mass of the photoelectron.
According to law of conservation of energy,
hν = Ф + ½ mv2max
= hν0 + ½ mv
½ mv2max = h (ν - ν0)
VERIFICATION OF LAWS OF PHOTOELECTRIC EMISSION BASED ON EINSTEIN’S PHOTOELECTRIC
EQUATION:
I) If ν < ν0, then ½ mv2max is negative, which is not
possible. Therefore, for Photoelectric emission to take
place ν > ν0.
ii) Since one photon emits one electron, so the number
photoelectrons emitted per second is directly proportional
to the intensity of incident light.
iii) It is clear that ½ mv2max α ν as h and ν0 are constant.
This shows that K.E. of the photoelectrons is directly
proportional to the frequency of the incident light.
iv) Photoelectric emission is due to collision between a
photon and an electron. As such there cannot be any
significant time lag between the incidence of photon and
emission of photoelectron. i.e. the process is
instantaneous. It is found that delay is only 10-8 seconds.
Application of Photoelectric Effect:-
1. Automatic fire alarm
2. Automatic burglar alarm
3. Scanners in Television transmission
4. Reproduction of sound in cinema film
5. In paper industry to measure the thickness of paper
6. To locate flaws or holes in the finished goods
7. In astronomy
8. To determine opacity of solids and liquids
9. Automatic switching of street lights
10. To control the temperature of furnace
11. Light meters used in cinema industry to check the light
YOU CAN WATCH OUR VIDEO
DOWNLOAD PDF 2- click here
0 Comments