Short Answer Type
Long Answer TypeDescribe briefly Planck's Quantum Theory.
This theory can be simply stated as:
(i) Radiation is associated with energy.
(ii) Radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy.
(iii) Each packet of energy is associated with a definite amount of energy and is known as quantum. In the case of light, the ‘quantum’ is known as ‘photon’.
(iv) The magnitude of quantum is directly proportional to the frequency of radiation.
E ∝ v
i.e. E = hv
where v = Frequency of radiation
h = Planck’s constant
= 6.625 x 10-34Js
(or 6.625 X 10-34 kg m2 s-1)
= 3.99 x 10-13 k Js mol-1
(v) A body can radiate or absorb energy in whole number multiples of a quantum i.e. nhv, where n = 1,2,3,4......etc.
A photon of wavelength 4 x 10-7 m strikes on metal surface, the work function of the metal being 2.13 eV. Calculate: (i) the energy of the photon (eV), (ii) the kinetic energy of the emission, and (iii) the velocity of the photoelectron (1 eV = 1.6020 10-19J).
Short Answer TypeLong Answer TypeThe work function for caesium atom is 1.9 eV. Calculate: (a) the threshold wavelength and (b) the threshold frequency of radiation. If the caesium element is irradiated with a wavelength 500 nm, calculate the kinetic energy and velocity of the ejected photoelectron.
Short Answer Type
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