Bohr’s model of the hydrogen atom to be no doubt an development over Rutherford’s nuclear model, as it might account for the stability and also line spectra of a hydrogen atom and also hydrogen-like ion (for example,
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Merits that Bohr’s theory :
(i) The experimental value that radii and energies in a hydrogen atom are in great agreement with that calculate on the basis of Bohr’s theory.(ii) Bohr’s principle of the stationary state of electron defines the emission and also absorption spectra that hydrogen-like atoms.(iii) The speculative values that the spectral lines of the hydrogen spectrum are in close agreement with the calculated by Bohr’s theory.
Limitations the Bohr’s concept :
(i) that does not describe the spectra of atom having an ext than one electron.(ii) Bohr’s atomic version failed come account for the effect of the magnetic ar (Zeeman Effect) or electrical field (Stark effect) on the spectra of atoms or ions. It to be observed that as soon as the source of a spectrum is placed in a solid magnetic or electric field, every spectral line more splits into a variety of lines. This observation can not be described on the basis of Bohr’s model.(iii) De Broglie suggested that electrons choose light have a twin character. It has actually particle and also wave characters. Bohr cure the electron only as a particle.(iv) one more objection come Bohr’s theory came indigenous Heisenberg’s hesitation Principle. According to this rule “It is impossible to recognize simultaneously the precise position and momentum the a little moving fragment like one electron”. The postulate of Bohr, that electrons revolve in well-defined orbits about the nucleus with well-defined velocities is thus not tenable.
Photo Electric result :
Sir J.J Thomson, observed that as soon as light that a details frequency strikes the surface ar of a metal, electrons room ejected from the metal. This phenomenon is known as the photoelectric effect and the ejected electrons are referred to as photoelectrons.A few metals, which have actually low ionisation power like Cesium, display this result under the action of visible light yet much much more show it under the action of more energetic ultraviolet light.
An evacuated tube has two electrodes associated to a resource of change voltage, through the steel plate whose surface ar is irradiated together the anode. Some of the photoelectrons that emerge from this surface have actually enough energy to reach the cathode despite its negative polarity, and they constitute the measured current. The slower photoelectrons space repelled before they acquire to the cathode. Once the voltage is increased to a details valueV0, of the bespeak of numerous volts, no an ext photoelectrons arrive, as suggested by the existing dropping to zero. This extinct voltage (or also referred as preventing potential) synchronizes to the best photoelectron kinetic energy
The experimental findings are summarised as below :
(i) electrons come the end as soon as the irradiate (of sufficient frequency) strikes the metal surface.(ii) The light of any type of frequency will certainly not have the ability to cause ejection of electrons from a metal surface. There is a minimum frequency, referred to as the threshold (or critical) frequency, which have the right to just cause the ejection. This frequency varies v the nature the the metal. The higher the frequency the the light, the an ext energy the photoelectrons have. Blue light results in faster electrons than red light.(iii) Photoelectric current is boosted with boost in the soot of light of the exact same frequency if emissions are permitted i.e., bright irradiate yields much more photoelectrons 보다 a dim among the exact same frequency, yet electron energies continue to be the same. Light must have actually a present of power particles or quanta of energy (hν). Suppose, the threshold frequency the light required to eject electron from a metal is ν0 when a photon of irradiate of this frequency strikes a metal it imparts its entire energy (hν0 )to the electron.
“This energy permits the electron come break far from the atom by overcoming the attractive influence of the nucleus”. Hence each photon deserve to eject an electron. If the frequency of irradiate is much less than V0there is no ejection of the electron. If the frequency of light is greater thanν0 (let it it is in ν), the photon that this light having higher energy (hν), will certainly impart some energy to the electron the is essential to eliminate it away from the atom. The excess energy would offer a particular velocity (i.e, kinetic energy) come the electron.
hν= hν0+K.Emax; hν= hν0+1/2 mv2; 1/2 mv2 =hν-hν0where,ν = frequency the the event lightν0 = threshold frequencyhν0is the threshold energy (or) the work function denoted through Φ=hν0 (minimum power of the photon to liberate electrons). That is continuous for specific metals and also is also equal to the ionization potential of gaseous atoms.
The kinetic energy of the photoelectrons increases linearly through a frequency of occurrence light. Thus, if the energy of the ejected electrons is plotted together a role of frequency, it outcomes in a directly line whose slope is equal to Plank’s constant ‘h’ and whose intercept is hν0.
It is vital to note that the expression requires (K.E)max. In reality, e– have actually K.E lesser than this.
Total energy falling on key = n h ν photon intensity
The soot of energy falling =
As they space emitted indigenous the cathode, they space in in between cathode & as such refresh coming the end from the cathode. This charge is termed as room charge.Variation the P.E present us for different photon intensities
Illustration 1: A photon of wavelength 5000 A strikes a steel surface, the work duty of the metal being 2.20 eV.
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Calculate (i) the energy of the photon in eV (ii) the kinetic power of the emitted photoelectron and (iii) the velocity of the photoelectron.Solution :(i) The power of the photon
Dual character (Particle and also Wave character of Matter and also Radiation) :
In situation of light, part phenomenon prefer diffraction and also interference deserve to be defined on the basis of its tide character, However, details another phenomenon such as black color body radiation and also photoelectric effect can be defined only on the basis bit nature. Thus, irradiate is said to have a dual character. Such research studies on light to be made by Einstein in 1905. luigi de Broglie, in 1924 prolonged the idea the photons to material particles such together electrons and also he proposed that matter additionally has a dual character-as wave and as a particle.