%20scale(-1%201)'/%3e%3c!--%20power%20symbol%20--%3e%3cpath%20fill='none'%20stroke='%23fff'%20stroke-width='28'%20stroke-linecap='round'%20d='M212.3,219.9%20A68,68%200%201%200%20299.7,219.9'/%3e%3cpath%20fill='none'%20stroke='%23FBBF24'%20stroke-width='24'%20stroke-linecap='round'%20d='M256,200%20V284'/%3e%3c/svg%3e){kind=small}
Physics · Chapter 1: Introduction to Physics
Branches of Physics
The main branches of physics: mechanics, heat, sound, light, electricity and magnetism, atomic, nuclear and plasma physics, plus astrophysics, biophysics and geophysics.
Key termRememberExampleWatch out
01Concept
Physics is a very big subject, so it is divided into branches. Each branch studies one kind of matter or energy. The branches are usually put into three groups: classical physics, modern physics and interdisciplinary branches that join physics with another science.
Classical physics
These branches explain the things we can see and feel in everyday life.
| Branch | What it studies | Everyday example |
|---|---|---|
| Mechanics | Motion of objects and the forces that cause it | A car speeding up; a cricket ball in flight |
| Heat and thermodynamics | Heat, temperature and how heat changes into work | A car engine; a refrigerator |
| Sound (acoustics) | How sound is produced and travels | Echoes in an empty room; the sound of a tabla |
| Light (optics) | How light behaves: reflection, refraction and colours | Mirrors, spectacles, a rainbow |
| Electricity and magnetism | Electric charges, currents and magnets | House wiring, electric motors in fans |
Modern physics
Around 1900, scientists found that classical physics could not explain very small things (atoms) or very fast things (close to the speed of light). New branches grew to explain them.
| Branch | What it studies | Example |
|---|---|---|
| Atomic physics | The atom as a whole, mainly its electrons | How a neon sign gives coloured light |
| Nuclear physics | The nucleus of the atom | Nuclear power plants; radioactivity |
| Particle physics | The smallest known particles, such as quarks and electrons | Experiments at CERN, where Pakistan is an associate member |
| Relativity | Objects moving close to the speed of light, and gravity | Clocks on GPS satellites need corrections |
| Quantum physics | Energy that comes in tiny packets (quanta) | Lasers; the chips in your phone |
| Solid-state physics | The structure and properties of solids | Semiconductors in computers and solar panels |
| Plasma physics | Plasma, the fourth state of matter | Lightning; the Sun |
Physics joined with other sciences
- Astrophysics: the physics of stars, planets and galaxies. Why stars shine.
- Biophysics: physics used to study living things. How nerves carry electrical signals.
- Geophysics: the physics of the Earth. Studying earthquakes; searching for oil and gas.
- Medical physics: physics used in hospitals. X-rays, CT scans and radiotherapy for cancer.
02Real World Examples
A motorbike uses several branches
Its engine uses thermodynamics, its gears use mechanics, its headlight uses optics and its battery uses electricity.
Earthquake warnings
Geophysicists at the Pakistan Meteorological Department record earthquakes with instruments called seismometers.
Cancer treatment
Medical physicists plan radiotherapy doses in cancer hospitals, so the radiation hits the tumour and spares healthy tissue.
Electricity from the nucleus
The Karachi and Chashma nuclear power plants use nuclear physics to make electricity.
03Practice Questions
Try to answer in your own words first, then open the model answer.
Short questions
Q1.What is the difference between classical and modern physics?Show answer
Answer
| Classical physics | Modern physics |
|---|---|
| Mostly developed before 1900 | Developed from about 1900 |
| Explains everyday objects and speeds | Explains very small (atoms) and very fast objects |
| Mechanics, optics, heat | Nuclear physics, relativity, quantum physics |
Q2.Define mechanics and thermodynamics with one example each.Show answer
Answer
- Mechanics: the study of motion and the forces that cause it. A car speeding up.
- Thermodynamics: the study of heat and how it changes into work. A car engine.
Q3.Differentiate between atomic physics and nuclear physics.Show answer
Answer
Atomic physics studies the whole atom, mainly its electrons. Nuclear physics studies only the nucleus and its changes, such as radioactivity and nuclear energy.
Q4.What is plasma physics?Show answer
Answer
Plasma physics studies plasma, the fourth state of matter. Plasma is a very hot gas whose atoms have lost electrons. Lightning and the Sun are plasma.
Q5.Name any two interdisciplinary branches of physics and say what they study.Show answer
Answer
- Biophysics: the physics of living things, such as how nerves carry signals.
- Geophysics: the physics of the Earth, such as earthquakes.
(Astrophysics and medical physics are also correct answers.)
Long questions
Q6.Describe the main branches of physics.Show answer
Answer
- Mechanics: motion and forces.
- Heat and thermodynamics: heat, temperature and engines.
- Sound (acoustics): production and travel of sound.
- Light (optics): reflection, refraction and colours of light.
- Electricity and magnetism: charges, currents and magnets.
- Atomic physics: the atom and its electrons.
- Nuclear physics: the nucleus and radioactivity.
- Plasma physics: the fourth state of matter.
- Astrophysics, biophysics and geophysics: physics applied to stars, living things and the Earth.