Dual Nature of Matter and Radiation
Electron Emission
The electrons in metals which are free to move known as free electrons. These electrons do not get ejected out of the surface of metal on their own due potential barrier or work function of the metal. But when a free electron gets extra energy then these electrons overcome the potential barrier and is ejected out. There are different ways in which electron emission take place.
Photoelectric effect
When electromagnetic radiations of suitable wavelength are incident on a metallic surface then electrons are emitted, this phenomenon is known as the photoelectric effect. And the emitted electrons are known as photoelectrons.
Experimental study of photoelectric Effect- When the light of frequency v and intensity I fall on the cathode, electrons are emitted from it. The electrons are collected by the anode and a current flows in the circuit. This current is known as photoelectric current.
The main points of observation are:
(a) At zero anode potential, a current exists. It means that electrons are emitted from the cathode with some kinetic energy.
(b) As anode potential is increased, current increase. This implies that different electrons are emitted with different kinetic energies.
(c) After a certain anode potential, current acquires a constant value called saturation current.
(d) At a certain negative potential, the photoelectric current becomes zero. This is called stopping potential (V0). Stopping potential is a measure of maximum kinetic energy of the emitted electrons. Let KEmax be the maximum kinetic energy of an emitted electron, then KEmax = eV0
(1) Variation of photoelectric current with the potential difference:
(2) Variation of current with intensity- The photoelectric current is found to be directly proportional to the intensity of incident radiation
(3) Effect of frequency- The Stopping potential is vary with the frequency of incident light linearly. Greater the frequency of incident light, greater the stopping potential.
Einstein's Photoelectric Equation
Einstein's photoelectric equation is,
where hv is the energy transferred to the electron, ϕ is the energy needed to escape or work function of the metal, the remaining energy is the kinetic energy of the electron.
The kinetic energy of the electron is, KEmax = eV0 (where V0 is stopping potential)
De-Broglie Waves
According to De-Broglie, every moving particle associated with a wave known as De-Broglie waves and the wavelength associated with a moving particle is known as De-Broglie.
De Broglie wavelength associated with moving particles
If a particle of mass m moving with velocity v
The kinetic energy of the particle is,
the momentum of the particle is
the wavelength associated with the particles is
De Broglie wavelength associated with the charged particles
Let a charged particle having charge q is accelerated by potential difference V.
The kinetic energy of this particle
Momentum of particle
The De Broglie wavelength associated with the charged particle
Davisson and Germer Experiment
Davisson and Germer experiment confirmed the wave-nature of electrons.
In this experiment when the electron beam is incident on a nickel target the electron scattered in all direction acting like waves. The detector detects the maximum intensity at a certain angle. And this maximum intensity is due to constructive interference, which confirmed the wave nature of light.
The De-Broglie wavelength (λ) associated with the electron is
If you're thinking of ways to score better in JEE 2021, check out
Rankup JEE: A 70-Day Score Booster Course for JEE Main April 2021
Prepare with best-in-class teachers from Kota & Delhi, having mentored 100+ double-digit JEE rankers. Comprehensive day wise study plan for last 70 days to become exam ready.
Short Notes on Dual Nature of Matter and Radiation Download PDF!
All India Free Mock Test for JEE Main | Attempt Now
Subscribe to YouTube Channel for JEE Exam
All the best!
Team BYJU'S Exam Prep
Sahi Prep hai toh Life set hai
Download BYJU'S Exam Prep, the best IIT JEE Preparation App
Comments
write a comment