Modern Physics

Introduction

Modern Physics is the branch of physics that deals with the post-Newtonian concepts in the world of physics. It typically includes topics such as relativity, quantum mechanics, atomic structure, nuclear physics, and particle physics.

Key Concepts

Relativity

Introduced by Einstein, it includes special and general relativity, dealing with motion at high speeds and gravity.

Quantum Mechanics

Study of particles at the atomic and subatomic scale, including wave-particle duality and quantum states.

Atomic Structure

Describes the structure of atoms, including electrons, protons, and neutrons, and their interactions.

Nuclear Physics

Focuses on the nucleus of the atom, radioactivity, nuclear reactions, and applications like nuclear energy.

Important Equations

E = mc²

Energy-mass equivalence from Einstein's theory of relativity.

E = hf

Energy of a photon where h is Planck’s constant and f is the frequency.

λ = h/p

de Broglie relation: wavelength of a particle with momentum p.

ΔE = -13.6 (1/n² - 1/m²) eV

Energy difference in electron transitions in the hydrogen atom.

Applications

Example Problems

1. Find the energy of a photon with frequency 5×10¹⁴ Hz.

Solution: E = hf = 6.63×10⁻³⁴ × 5×10¹⁴ = 3.315×10⁻¹⁹ J

2. Calculate the energy equivalent of 1 gram of mass.

Solution: E = mc² = 0.001 × (3×10⁸)² = 9×10¹³ J

3. Determine the de Broglie wavelength of an electron moving at 2×10⁶ m/s.

Solution: λ = h/p = 6.63×10⁻³⁴ / (9.11×10⁻³¹ × 2×10⁶) ≈ 3.63×10⁻¹⁰ m