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Chapter 2 Structure of The Atom Solutions

Question - 11 : - A 25 watt bulb emits monochromatic yellowlight of wavelength 0.57 μm. Calculate the rate of emission of quanta persecond.

Answer - 11 : -

Question - 12 : - Electrons are emitted with zero velocity froma metal surface when it is exposed to radiation of wavelength 6800 A. Calculatethreshold frequency (v0) and work function (W0) of themetal.

Answer - 12 : -

Question - 13 : - What is the wavelength of the light emittedwhen the electron in a hydrogen atom undergoes transition from the energy levelwith n = 4 to energy level n = 2 ? What is the colour corresponding to this wavelength? (Given RH = 109678 cm-1)

Answer - 13 : -

Question - 14 : - How much energy is required to ionise ahydrogen atom if an electron occupies n = 5 orbit ? Compare your answe r withthe ionisation energy of H atom (energy required to remove the electron from n= 1 orbit)

Answer - 14 : -

Question - 15 : - What is the maximum number of emission lineswhen the excited electron of a hydrogen atom in n = 6 drops to the ground state?

Answer - 15 : - The maximum no. of emission lines = n(n–1)2 = 6(6–1)2 =3× 5 = 15

Question - 16 : - (i) The energy associated with first orbit inhydrogen atom is – 2.17 × 10-18 J atom-1. What isthe energy associated with the fifth orbit ?
(ii) Calculate the radius of Bohr’sfifth orbit for hydrogen atom.

Answer - 16 : -

(ii) For hydrogenatom ; rn = 0.529 x n2 Å
r5 = 0.529 x (5)2 = 13.225 Å = 1.3225 nm.

Question - 17 : - Calculate the wave number for the longestwavelength transition in the Balmer series of atomic hydrogen.

Answer - 17 : -

Question - 18 : - What is the energy in joules required to shiftthe electron of the hydrogen atom from the first Bohr orbit to the fifth Bohrorbit and what is the wavelength of light emitted when the electron returns tothe ground state ? The ground state electronic energy is – 2.18 × 11-11 ergs.

Answer - 18 : -

Question - 19 : - The electronic energy in hydrogen atom isgiven by En (-2.18 × 10-18 s) / n2J.Calculate the energy required to remove an electron completely from the n = 2orbit. What is the longest wavelength of light in cm that can be used to causethis transition?

Answer - 19 : -

Question - 20 : - Calculate the wavelength of an electron movingwith a velocity of 2.05 × 107 m s-1.

Answer - 20 : -

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