Chapter 2 – Structure of Atom
Assignment 4
Q.1. Calculate the minimum amount of energy that
the photons must possess to eject electrons from cesium metal.
The threshold frequency of cesium metal is 4.6 × 1014
s–1 (h = 6.63 × 10–34 J s).
[Ans: 3.05 × 10-19 J ]
Q.2. When light of wavelength 470 nm falls on the surface of potassium metal, electrons are emitted with a velocity of 6.4 × 104 m s–1. What is the minimum energy required per mole to remove an electron from potassium metal ?
[Ans: 253.6 kJ mol–1 ]
Q.3. The threshold frequency for a metal 'X' is 7.0 × 1014 s–1. Calculate the kinetic energy of an electron emitted when radiation of 1.0 × 1015 s–1 strikes the metal.
[Ans: 1.99 × 10–19 J ]
Q.4. Calculate the kinetic energy of the ejected electron when ultra-violet radiation of frequency 1.6 × 1015 s–1 strikes the surface of potassium metal. Threshold frequency of potassium is 5 × 1014 s–1 (h = 6.63 × 10–34 J s).
[Ans: 7.29 × 10–19 J ]
Q.5. Electrons are emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength 6800 Å. Calculate threshold frequency (νo) and work function (Wo) of the metal.
[Ans: 4.41 × 1014 s–1, 2.92 × 10–19 J ]
Q.6. Calculate the wavelength and energy of radiation emitted for the electronic transition from infinity to the stationary state of the hydrogen atom.
[ Ans: l = 9.11 × 10–8 m, E = 2.18 × 10–18 J ]
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