**CBSE NOTES CLASS 12 PHYSICS **

**CHAPTER 12 ATOMS**

**Radius of orbit of electron** is given by

$$\mathrm{r}=\frac{4\mathrm{\pi}{\mathrm{\epsilon}}_{0}{\mathrm{n}}^{2}{\mathrm{h}}^{2}}{4{\mathrm{\pi}}^{2}\mathrm{m}\mathrm{Z}{\mathrm{e}}^{2}}=\frac{{\mathrm{\epsilon}}_{0}{\mathrm{n}}^{2}{\mathrm{h}}^{2}}{\mathrm{\pi}\mathrm{m}\mathrm{Z}{\mathrm{e}}^{2}}$$

where,

n = principle quantum number,

h = Planck’s constant,

m = mass of an electron,

Z = atomic number and

e = electronic charge.

Substituting the values of *h*, *m*, ε_{o} and *e *, we get,

- r

_{1}= 5.29 × 10

^{–11}m.

**Bohr radius**, and is represented by

*a*

_{o}.