Class 12 Physics NCERT Solutions

In this chapter, you are going to learn about atom and atoms collisions. Every particular substance in this universe is made up of atoms. Without atoms, there won’t be any substance. An atom is a tiny particle that cannot be seen by your naked eyes. The molecules collide(come into conflict) with the combination of kinetic energy to bring the chemical reaction; it is done in collision theory.

Let me give an example of the question:

Question 12.9: A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?
Solution 12.9: From the formula

En = ‒13.6/n2 eV
For n = 3 to n = 1
E3 – E1 = 12.09 eV or (near to) 12.5 eV

This energy difference includes both the Lyman and Balmer series.
At room temperature, most of the hydrogen atoms are in ground state. So, n = 1, and the energy difference indicates the final n to be 2 or 3.

Lyman series

For n = 2
(1/λ) = R [(1/12) ‒ (1/22)]
λ = 122 nm
For n = 3, 𝜆= 103 nm

Balmer series,

For n = 3,
1/λ = R [(1/22) ‒ (1/32)]
⇒ λ = 656 nm.
This type of theory and problems you are going to learn in this ex 12.9 chapter 12 in class 12th physics.


In this, the collision of molecules is done with the kinetic energy by the theory of both Lyman and Balmer series based on the given example u can solve more problems.

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