**Quantum Theory of Radiation:**This theory was
proposed by German physicist, **Max Planck
**in 1900, to explain the phenomena of black body radiations. According to
this theory;

**“Energy is emitted or absorbed by a body not
continuously but discontinuously in the form of small packets or bundles of
energy known as Quanta. The energy of a body can increase or decrease by
1,2,3,4,5,…..n quanta but not by fractions of a quanta."**

Thus, the energy of radiation is proportional to its
frequency and inversely proportional to wave length.

**Solved Questions:**

### (1) Calculate the energy per mole of photon of electromagnetic radiations of wavelength 4000Å.

**Practice Questions:**

1.** **A photon of light of wavelength 6000 Å has energy E. Calculate the
wavelength of photon of a light which has energy/photon 4E.

2. Calculate the wavelength, wave
number and frequency of photon having its energy 5 electron volt.

3. Iodine
molecule dissociates into atoms after absorbing light of 4500Å. If one quantum
of radiation is absorbed by each molecule, calculate the kinetic energy of iodine
atoms. (Bond energy of I_{2} = 240 kJ mol^{–1})

**Answer Keys: **

1. Lemda-2=
1500 Å

2. 2.475 ×
10^{–5} cm, 4.04 × 10^{4} cm, 1.212 × 10^{15} Hz

3. 2.16 × 10^{–20}
J

**Related Questions:**

**(1) What is the difference between 2p and 3p orbitals?**

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