CBSE Class 12 Physics Dual Nature Of Matter And Radiation Notes Set 01

CBSE Class 12 Physics Dual Nature Of Matter And Radiation. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations. 

7. DUAL NATURE OF MATTER & RADIATION

GIST

ELECTRON EMISSION

1. There are three types of electron emission, namely, Thermionic Emission, Photoelectric Emission and Field Emission.

2. The minimum energy required by an electron to escape from the metal surface is called work function.

3. Work function is conveniently expressed in electron volts ( e V )

4. One electron volt is the energy gained or lost by an electron while passing through a potential difference of one volt.

PHOTOELECTRIC EFFECT

1. The minimum energy required by an electron to come out from metal surface is called the work function of a metal.

2. Photo electric effect is the phenomenon of electrons by metals when illuminated by light of suitable frequency

3. Photo electric current depends on

i) The intensity of incident light

ii) The potential difference applied between two electrodes

iii) The nature of the emitter material

EXPERIMENTAL STUDY OF PHOTOELECTRIC EFFECT

1. The minimum negative potential given to the anode plate for which the photo electric current becomes zero is called stopping potential.

2. The stopping potential Vo depends on i) The frequency of incident light and ii) the nature of emitter material. For a given frequency of incident light, the stopping potential is independent of its intensity.

eV_o =(1/2)m v²_max =K_max

3. Below a certain frequency (threshold frequency) γ₀ , characteristics of the metal , no photo electric emission takes place, no matter how large the intensity may be.

EINSTEINS PHOTO ELECTRIC EQUATION: ENERGY QUANTUM OF RADIATION

1. Light is composed of discrete packets of energy called quanta or photons.

2. The energy carried by each photon is E = hν, where ν is the frequency and momentum p= h/λ.

The energy of the photon depends on the frequency γ of the incident light and not on its intensity.

3. Photo electric emission from the metal surface occurs due to absorption of a photon by an electron

4. Einstein’s photo electric equation: K_max = hν – φ0 or eV₀ = hν - φ₀.

PARTICLE NATURE OF LIGHT: THE PHOTON

1. Radiation has dual nature: wave and particle. The wave nature is revealed in phenomenon like interference, diffraction and polarization. The particle nature is revealed by the phenomenon photo electric effect.

2. By symmetry, matter also should have dual nature: wave and particle. The waves associated with the moving material particle are called matter waves or De Broglie waves.

3. The De Broglie wave length (λ) associated with the moving particle is related to its moment p as: λ =h/p = h/mv

4.An equation for the De Broglie wavelength of an electron accelerated through a potential V. Consider an electron with mass ‘m’ and charge ‘e’ accelerated from rest through a potential V.

K = eV

K = 1/2mv² = p²/2m

P² = 2mK

P = √2mK = √2meV

λ = h/ √2meV

Substituting numerical values of h, m and e

λ = (1.227/√V) nm.

5. Heisenberg’s Uncertainty Principle states that it is not possible to measure both the position and velocity of an electron (or any other particle) at the same time exactly. There is always an uncertainty Δx in the specification of position and an uncertainty Δp in the specification of momentum.

Δx Δp = ћ, where ћ = h/2π

6. Davisson and Germer experiment proves the existence of wave nature of electron.

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