# Important Questions and Answers: Quantization of Energy

**1. The atom is stable in ground state. Why?**

*Ans:* When the atom is in ground state, there will be no state of lower energy to which downward transition can occur. So, the atom in the ground state is stable.

**2. How is Paschen series originated in hydrogen atom ?**

*Ans:* When electron from higher energy state jump to third orbital, Paschen series of spectral lines obtained. This series lies within infrared region. Wavelength of the hydrogen atom in this series is calculated by the formula.

$$\text{f} = \frac{1}{\lambda} = R \left ( \frac{1}{3^2}- \frac{1}{n_2^2} \right )$$

**3. What is excitation potential and hydrogen potential ?**

The minimum energy required for electron to jump from ground state to any higher state is called excitation energy and the corresponding potential is called excitation potential.

**4. What is De-broglie wave?**

*Ans: *According to De Broglie every particle in motion has wave character. The wave associated with matter is called matter wave. The wavelength associated with the the matter is given by:

$$\lambda = \frac{h}{p} = \frac{h}{mv} $$

Where h is the Planck’s constant and p is the momentum of the wave.

**5. What is laser? What are the properties of laser?**

*Ans:* A laser is a light source that produces a beam of highly coherent and monochromatic light.

**Properties of laser:**

- The laser light is nearly monochromatic.
- They do not show the tendency to diverge at all.
- The beam is very intense.
- The light is coherent and in phase with each other.

**6. What is population inversion and optical pumping ?**

*Ans:*** Population inversion**: Generally, the number of electrons is greater in ground state and only a few are available on excited state due to thermal energy. But if somehow we make the number of electrons in the excited state more than that of in ground state, such condition is called population inversion.

**Optical pumping**: The method of achieving population inversion by supplying energy to ground state electrons by the incidence of photons is called optical pumping.

**7. A photon and electron has got same De-Broglie wavelength. Which has greater total energy?**

*Ans: *We know that, De-Broglie wavelength is given by:

$$\lambda = \frac{h}{ \sqrt{2mE}} $$

$$or, \lambda = \frac{h^2}{ 2mE} $$

$$or, E = \frac{h^2}{2m \lambda ^2}$$

Since λ is same for both the particles,

$$ \therefore E \propto \frac{1}{m}$$

Since the energy is inversely proportional to mass and as the mass of electron is less than of photon, so energy of electron is greater.

**8. What is uncertainty principle?**

*Ans: *According to this principle: “Simultaneous determination of momentum and position of an electron precisely is not possible.

If uncertainty in measurement of momentum is Δp and uncertainty in measurement of position is Δx, then:

$$\Delta p \times \Delta x \geq \frac{h}{4 \pi}$$

Here h is the Planck’s constant.

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