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नवीनतम संदेश
2021-07-21 09:53:36
Dear Aspirants,
"There is no goal in life that cannot be achieved with commitment and hard work."
Wishing you all and your family a very Happy Eid- ul- Adha.
Thanks & Regards
@physicswallahlakshyavideos
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56 views06:53
2021-07-20 22:01:15
#Latest #JEE
JEE Main 20 July Physics Shift-2 memory based question paper with Solution
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2021-07-20 22:01:01
JEE MAIN 2021
JEE Main 20 July Evening Shift memory based question papers by Resonance
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2021-07-20 16:49:24
JEE Main 20 July Physics Morning Shift memory based question paper.pdf
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JEE Main 20 July Mathematics Morning Shift memory based question paper.pdf
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JEE Main 20 July Chemistry Morning Shift memory based question paper.pdf
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2021-07-20 16:49:23
JEE MAIN 2021
20 July Morning Shift memory based question papers by Resonance
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2021-07-20 16:27:15
Having doubts while solving modules and DPPs ?
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229 views13:27
2021-07-19 15:28:56
Notes on Atomic Physics
e/m of an electron (Thomson Method):-
(a) e/m of a particle is called the specific charge of the particle.
e/m = v/rB
Here, r is the radius of curvature, B is the strength of magnetic field, v is the velocity, e is the charge on cathode ray particle and m is the mass.
(b) v = E/B
Electric field:- E = V/d
Photo electric effect:- Photo-electric effect is the phenomenon of emission of electrons from the surfaces of certain substances, mainly metals, when light of shorter wavelength is incident upon them.
Effect of collector’s potential on photoelectric current:-
(a) Presence of current for zero value potential indicates that the electrons are ejected from the surface of emitter with some energy.
(b) A gradual change in the number of electrons reaching the collector due to change in its potential indicates that the electrons are ejected with a variety of velocities.
(c) Current is reduced to zero for some negative potential of collector indicating that there is some upper limit to the energy of electrons emitted.
(d) Current depends upon the intensity of incident light.
(e) Stopping potential is independent of the intensity of light.
Effect of intensity of light:- The photoelectric currentis directly proportional to theintensity of incident radiation.
Effect of frequency of light:-
(a) Stopping potentialdepends upon thefrequency of light. Greater the frequency of light greater is the stopping potential.
(b) Saturation current is independent of frequency.
(c) Threshold frequency is the minimum frequency, that capable of producing photoelectric effect.
Laws of Photoelectricity:-
(a) Photoelectric effect is an instantaneous process.
(b) Photoelectric current is directly proportional to the intensity of incident light and is independent of its frequency.
(c) The stopping potential and hence the maximum velocity of the electrons depends upon the frequency of incident light and is independent of its frequency.
(d) The emission of electrons stops below a certain minimum frequency known as threshold frequency.
Energy contained in bundle or packet:-
E = hf = hc/λ
Here h is the Planck’s constant and f is the frequency.
Work function:- It is defined as the minimum energy required to pull an electron out from the surface of metal. It is denoted by W0.
Einstein’s equation of photoelectric effect:-
(a) ½ mvmax2 = hf – W0
(b) ½ mvmax2 = hf – hf0 = h(f- f0) = h [c/λ – c/λ0]
(c) eV0 = hf - W0
(d)V0 = [(h/e)f] – [W0/e]
Here f0 is threshold frequency.
Threshold frequency (f0):- f0 = work function/h = W/h
Maximum kinetic energy of emitted photo electrons:-
?Kmax= ½ mvmax2 = eV0
Threshold wavelength:- λ0 = c/f0 = hc/hf0 = hc/W
Slope of V0~ v graph:- Slope= h/e
Rest mass of photon = 0, Charge = 0
Energy of photon:- E = hf = hc/λ
Momentum of photon:- p = E/c = h/λ = hf/c
Mass od photon:- m = E/c2 = h/cλ = hf/c2
For electron, λe = [12.27/√V]Å
For proton, λp = [0.286/√V]Å
For alpha particle, λα = [0.286/√V]Å
For particle at temperature T, λ = h/√3mKT (E = 3/2 KT)
The wavelength of electron accelerated by potential difference of V volts is:-
λe= [12.27/√V]Å
Number of photons:-
(a) Number of photons per sec per m2, np = Intensity/hf
(b) Number of photons incident per second, np = Power/hf
(c) Number of electrons emitted per second = (efficiency per surface)× (number of photons incident per second)
Compton wave length:-
(a) λc = h/m0c
Here h is the Planck’s constant, m0 is the rest mass of electron and c is the speed of light.
(b) Change in wavelength:- λ' – λ =λc (1-cos?)
de Broglie wavelength (λ):-λ = h/mv = h/√(2mE) = h/√(2meV)
In accordance to Bohr’s postulate of atomic structure, the angular momentum of an electron is an integral multiple of h/2π.
So, mvr = nh/2π
Bragg’s diffraction law:- 2dsinθ = nλ
Here λ is the wavelength of electron and d is distance between the planes.
Rutherford’s atomic model (α-particle scattering):-
(a) N(θ) ∝ cosec4(θ/2)
(b) Impact parameter, b = [(Ze2) (cot θ/2)]/[(4πε0)E]
Here, E = ½ mv2 = KE of theα particle@iit_jee_main
6.0K viewsedited 12:28
2021-07-16 19:10:11
#Physics #ImportantConcept #jee #neetCentre Of MassC-Frame Concept If we attach an Inertial frame of Reference with the centre of mass of many particle system then centre of mass in that frame of reference would be at rest or, Vcm=0 , and such type of reference frames are known as centre of mass frame of reference.
Total Linear Momentum of a many particle system is zero in centre of mass frame of reference i.e., pcm=MVcm=0 since Vcm=0.
Therefore C-reference frames are also known as zero momentum reference frames.
Since in absence of any external force the centre of mass of any system moves with constant velocity in inertial frame of reference therefore for a many particle system C-frame of reference is an inertial frame of reference.
Reference frames connected to laboratory are known as L-frame of reference or laboratory frame of reference.@iit_jee_main
@physicswallahlakshyavideos
1.7K viewsedited 16:10
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