NCERT Solutions for Class 12 Physics Chapter 12: Atoms

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NCERT Solutions for Class 12 Physics Chapter 12 Atoms are given in this article. Atoms are the smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. Atom is the basic building block of chemistry.

Unit 8 Atoms and Nuclei along with Unit 7 Dual Nature of Radiation and Matter has a weightage of 12 marks in the CBSE Board examinations. The Class 12 Physics Chapter 12 NCERT Solutions cover the concepts of Atomic Spectra, Magnetic Quantum Number, and energy levels.

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NCERT Solutions for Class 12 Physics Chapter 12

The NCERT solutions for Class 12 Physics Chapter 12: Atoms is given below.

NCERT Solutions

CBSE Class 12 Physics Chapter 12 – Topics Covered

Thomson’s Atomic Model: Every atom is a uniformly positive charged sphere of radius of the order of 10^-10 m, in which the entire mass is distributed uniformly and negatively charged electrons are randomly embedded randomly.

Limitations of Thomson’s Atomic Model

1. It couldn’t explain the origin of spectral series of hydrogen and other atoms.

2. It couldn’t explain the large angle scattering of α-particles.

Bohr Model of the Hydrogen Atom: An electron can revolve in certain non-radiating orbits for which the angular momentum of electron is an integer multiple of (h/2π).

$r_n = n^2({h^2 \epsilon_o \over \pi mZe^2})$

Hydrogen Spectrum Series: Each element emits a radiation spectrum, which is characteristic of the element itself. The spectrum is known as the line spectrum.

Hydrogen spectrum consists of 5 series – Lyman Series, Balmer Series, Paschen Series, Brackett Series, and Pfund Series.

Wave Model is based on wave mechanics. Quantum numbers are the numbers that are required to completely specify the state of the electrons.

In the presence of a strong magnetic field, the 4 quantum number are Principle quantum number, Orbital angular momentum quantum number, Magnetic quantum number, and Magnetic spin angular momentum quantum number.

Also Read:

Chapter 12 Related Articles
Structure of atom	Atomic Number	Mass Number
Subatomic Particles of Atom	Atomic Radii	Atomic Energy Level
NCERT Solution for class 12 Physics	Dalton’s Atomic Theory	Atomic Orbitals
Thomson's Atomic Model	Alpha-Particle scattering and Rutherford's Nuclear Model of Atom	Avogadro's Number
Particle Physics	Laser Light	Alpha Particle Mass

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CBSE CLASS XII Related Questions

1.
An equiconvex lens of focal length $15$ cm is cut into two equal plano-convex halves. The focal length of each half will be:
- $30$ cm
- $20$ cm
- $15$ cm
- $7.5$ cm
View Solution
2.
(a) An electric field $\vec{E}$ is established across the ends of a cylindrical conductor of length $L$ and area of cross-section $A$. Discuss how electrons attain an average velocity, independent of time. Hence, obtain a relation between current in the conductor and this ‘average velocity’ of electrons.
(b) (i) This ‘average velocity’ is found to be a few $\text{mm}\,\text{s}^{-1}$ for currents in range of a few amperes. How then is current established almost the instant a circuit is closed?
(ii) Two copper wires having their radii in the ratio of $3:2$ are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.
View Solution
3.
The equivalent mass of a photon of wavelength $100\ \text{nm}$ is:
- $2.21\times 10^{-35}\ \text{kg}$
- $6.63\times 10^{-33}\ \text{kg}$
- $1.11\times 10^{-35}\ \text{kg}$
- $3.31\times 10^{-33}\ \text{kg}$
View Solution
4.
(a) A particle of charge $q$ and mass $m$ is accelerated through a potential difference $V$. Deduce an expression for the de Broglie wavelength associated with the particle.
(b) Plot a graph for a particle of charge $q$ and mass $m$ showing variation of de Broglie wavelength $\lambda$ with $\dfrac{1}{\sqrt{V}}$, where $V$ is the potential difference through which the particle is accelerated.
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5.
(i) With the help of a labelled diagram, explain the principle, construction and working of an a.c. generator.
(ii) Deduce an expression for the induced emf in the coil of the generator.
(iii) If $T$ is the time period of the rotation of the coil, at what values of $T$ in a cycle, the emf generated is maximum?
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6.
(i) Define the terms (I) resonant frequency, and (II) power factor of a series LCR circuit. For what value of the power factor will the power dissipated in the circuit be maximum?
(ii) An inductor of $\dfrac{5}{\pi}$ H, a capacitor of $\dfrac{50}{\pi}\ \mu\text{F}$ and a resistor of $400\ \Omega$ are connected in series across an ac voltage $v = 140 \sin(100\pi t)$ V. Calculate:
(I) impedance of the circuit, and
(II) rms value of current that flows in the circuit.
(Take $\sqrt{2} = 1.4$)
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