Modern Physics
A complete physics website covering atomic structure, radioactivity, photoelectric effect, quantum theory, nuclear physics, semiconductors, Einstein’s theory, formulas, diagrams, solved examples, and exercises.
1. Atomic Structure
An atom consists of electrons revolving around a nucleus containing protons and neutrons.
2. Photoelectric Effect
The emission of electrons from a metal surface when light falls on it is called photoelectric effect.
3. Quantum Theory
According to Planck’s quantum theory, energy is emitted or absorbed in discrete packets called quanta.
| Symbol | Meaning |
|---|---|
| E | Energy |
| h | Planck’s Constant |
| f | Frequency |
4. Radioactivity
The spontaneous disintegration of unstable nuclei is called radioactivity.
Types of Radiation
| Radiation | Nature |
|---|---|
| Alpha (α) | Helium nucleus |
| Beta (β) | Electron |
| Gamma (γ) | Electromagnetic wave |
5. Nuclear Physics
Nuclear physics deals with properties and reactions of atomic nuclei.
This equation given by Einstein shows relation between mass and energy.
Nuclear Reactions
- Nuclear Fission
- Nuclear Fusion
6. Semiconductors
Semiconductors are materials whose conductivity lies between conductors and insulators.
Types of Semiconductors
- N-type Semiconductor
- P-type Semiconductor
7. Einstein’s Theory of Relativity
Einstein proposed that space and time are interconnected.
Mass can be converted into energy and vice versa.
Example
Find energy equivalent of 1 kg mass.
E = 1 × (3 × 10⁸)²
E = 9 × 10¹⁶ J
8. Practice Exercises
Short Questions
- Define photoelectric effect.
- State Planck’s quantum theory.
- What is radioactivity?
- Write Einstein’s mass-energy equation.
- Define semiconductor.
Numerical Problems
- Find energy of photon of frequency 5 × 10¹⁴ Hz.
- Find energy equivalent of 2 kg mass.
- Calculate energy using E = hf where h = 6.63 × 10⁻³⁴ Js and f = 10¹⁵ Hz.
9. Formula Summary
| Topic | Formula |
|---|---|
| Photon Energy | E = hf |
| Mass-Energy Relation | E = mc² |
| Wave Energy | E = hc/λ |