Ncert Solutions Physics Class 12th

The principle of mass-energy equivalence, given by Einstein's equation:

$E = mc^2$It states that mass and energy are interchangeable.

A small amount of mass can be converted into a large amount of energy because the speed of light $(c = 3 \times 10^8 \, \text {m/s})$ is very large and appears squared in the equation.

Significance in Nuclear Reactions:

• Helps in calculating the energy release in Nuclear Reactions
• Provides explanation for powering Nuclear Reactors and the Sun
• Explanation of Binding Energy of Nucleous

Nuclear Binding Energy is the amount of energy required to completely dismantle a nucleus into its individual protons and neutrons which is equivalent to the amount of energy to form a nucleous from its constituent nucleons (protons and neutrons).

Binding energy is calculated using Einstein's mass-energy equivalence relation:

$B.E. = \Delta m \cdot c^2$Where:

• $\Delta m$ = mass defect (in kg or amu)

• $c$ = speed of light $(3 \times 10^8 \, \text {m/s})$ (3*108m/s)

As per the NCERT Textbooks, Thomson proposed a Atomic Structure of Atom that tells" An atom consists of a positively charged sphere in which the electrons are embedded like the seeds are embedded in watermelon. This model is often compared to a pudding or watermelon with electrons distributed like raisins or plums, also known as “plum pudding model.”

The presesnt day theory for structure of Atom is developed through many discoveries and hypothesises. In class 12 Physics, Atom chapter includes development of the sturucture of atom, and theories in the path of development of present theory. Students can check the ordered points below;

1. Thomson's Model of the Atom
2. Rutherford's Nuclear Model
3. Bohr's Model of the Hydrogen Atom
4. De Broglie's Hypothesis
5. Energy Emission Spectrum

These throries have been used to introduced the current theory of structure of atom.

Students who are preparing for the class 12 board exams needs additional practice questions after completing the NCERT Exercises. We have provided practice questions with accurate and atep-by-step solutions for students to better prepare for the board exams. Students can check the below provided link to access our additional practice questions along with previous year questions.

Chapter 12 Atoms NCERT Solutions 

The Davisson-Germer experiment was conducted to test the De-broglie hypothesis and know wave nature of electrons. In this experiment, a beam of electrons was emitted from an electron gun with known acceleration to strike a nickel crystal placed inside a vacuum chamber.

After striking the surface, electrons are scattered from the crystal surface at different angles. The diffraction pattern obtained through this experiment was similar to that produced by X-rays, which is wave.

The Davisson-Germer experiment provided the first experimental proof of the wave nature of matter and de Broglie's hypothesis right.

Significance of de Broglie's Hypothesis in Modern Physics (NCERT-based answer):

De Broglie's hypothesis is a revolutionary idea which changed the understanding of matter and wave as we know it. This hypothesis introduced the concept that particles of matter, like electrons, and Proton, can behave like wave and have wave-like properties, just as light exhibits both wave and particle nature.

According to de Broglie, any moving particle has a wavelength given by:

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

where $\lambda$ is the wavelength, $h$ is Planck's constant, $m$ is the mass, and $v$ is the velocity of the particle.

The net magnetic flux through any closed surface is zero, according to Gauss's Law for magnetism.
Mathematically,
? B · dA = 0.
It states that all magnetic field lines that enter a surface must exit from it as well. In this way, it is different from the electric charges which can exist independently as positive and negative.

The Earth's magnetic field makes a magnetic inclination or dip with the horizontal plane at a particular location. It shows how much the magnetic field is tilted from the horizontal. It gets tilted due to the Earth's magnetic nature. The formula is:
tan I = B_V / B_H,
where B_V is the vertical component and B_H is the horizontal component of the Earth's magnetic field.

The angle between the magnetic north (the direction a compass points) and the geographic north (true north) is the magnetic declination. This angle can change over time due to changes in the Earth's magnetic field and varies with location on Earth. It is important for navigation where accurate directional orientation is crucial, especially in marine and aviation transport. The declination helps in avoiding navigational errors as it ensures that compass readings are corrected.