Class 12 Physics Important Chapter 12 Atoms

Class 12 Physics Important Chapter 12 Atoms Solutions English Medium As Per The New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters ASSEB Class 12 Physics Additional Solutions in English and select need one. NCERT Class 12 Physics Additional Solutions Download PDF. HS 2nd Year Physics Important Solutions.

Class 12 Physics Important Chapter 12 Atoms

Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 12 Physics Additional Question Answer are part of All Subject Solutions. Here we have given HS 2nd Physics Important Solutions English Medium for All Chapters, You can practice these here.

Atoms

Chapter: 12

IMPORTANT QUESTION AND ANSWER

Answer The Following Questions:

1. Out of three radiations of wavelengths 2000A, 5000 Å and 1000 Å, which one responsible Lyman series of hydrogen spectrum? 

Ans. 1000 Å, because Lyman series lies in the ultraviolet region of the spectrum.

2. Name the physical quantities which are quantised in Bohr’s basic postulates of atomic model.

Ans. Energy state and the angular momentum are quantized in Bohr’s basic postulates of atomic model.

3. What was the main conclusion of Rutherford’s experiment on the scattering of alpha particles by thin foil?

Ans. Rutherford concluded that all the positive charge and almost entire mass of an atom is surrounded in a very small central region called nucleus of the atom.

4. Define the distance of closest approach.

Ans. Distance of closest approach is defined as the minimum distance of the charged particle at which initial kinetic energy of particle is equal to potential energy due to charged nucleus.

5. Show that the shortest wavelength lines in Lyman, Balmer and Paschen series have their wavelengths in the ratio 1:4:9.

Ans. For shortest wavelength of Lyman series, n1 = 1 n2 = ∞ 

∴ 1/⋋_LS = [ 2/ 1² – 1/ ∞ ] = R

⋋_LS  = R/1 

For shortest wavelength of Balmer series, n₁ = 2 , n₂ = ∞

6. Obtain Bohr’s quantisation conduction on the basis of the wave nature of an electron.

Ans: According to de Broglie, an electron has wave nature and its wavelength is given by λ= h​/mv​. For a stable orbit, the circumference of the orbit must be an integral multiple of the electron’s wavelength, i.e 2πr =  nλ. Substituting the value of λ, we get mvr = nh/2π which is Bohr’s quantisation condition. This means the electron can revolve only in those orbits where its angular momentum is quantised.

7.  Mention two limitations of Rutherford’s model of atom.

Ans: (i) This theory does not explain the fine structure of spectral line in the hydrogen atom.

(ii) It could not explain experimentally observed phenomena such as Zeeman effect, Stark effect etc.

8. Explain what is red shift and blue shift of light wave.

Ans: Red Shift: When a light source moves away from the observer, its wavelength increases, and light shifts toward the red end of the spectrum.

Blue Shift: When a light source moves toward the observer, its wavelength decreases, shifting the light toward the blue end.

9. Describe in brief the process of gamma radiation.

Ans: Gamma radiation is a type of electromagnetic radiation emitted by an atomic nucleus during a transition from a higher energy state to a lower one. It often follows alpha or beta decay, and the nucleus emits high-energy gamma photons without changing its atomic number or mass number.

10. Deduce the expression for the total energy of the electron in the nth orbit of a hydrogen atom in the Bohr model.

Ans: Bohr showed that the total energy of an electron in a hydrogen atom is:

Substituting constants, we get:

11. In hydrogen spectrum, the shortest wavelength in Balmer Series is given. What will be the shortest wavelength in Brackett Series?

Ans: Using the Rydberg formula from Bohr model.

For Brackett Series (nₓ → 4), shortest wavelength corresponds to ni = ∞ so:

12. In the light of Rutherford’s atom model, discuss the stability of an atom and state its inability to explain line emission spectrum.

Ans: Stability problem: Rutherford’s model suggests electrons revolve around the nucleus like planets. But according to classical physics, accelerating electrons should lose energy and spiral into the nucleus. This means atoms should not be stable — which contradicts reality.

Spectral lines: Rutherford’s model also fails to explain why atoms emit radiation at only certain wavelengths (line spectra). For example, hydrogen shows discrete spectral lines, which cannot be explained by continuous radiation from orbiting electrons.