SSC CGL Complete Physics Notes
Exhaustive physics fundamentals, SI units, scientific measuring instruments, inventions, discoveries, and system unit conversions for SSC CGL 2026.
1. Units & Systems of Measurement
Characteristics of a Unit
The chosen standard used for measuring a physical quantity is called a unit. It should be: well defined, easy to reproduce, easy to compare, internationally accepted, and independent of changes in physical conditions.
Unit Types: Fundamental Units and Derived Units. Internationally accepted systems include CGS, MKS, FPS, and SI Units.
Seven Fundamental SI Units
- Length: metre (M)
- Temperature: kelvin (K)
- Mass: kilogram (Kg)
- Luminous intensity: candela (Cd)
- Time: second (S)
- Amount of substance: mole (Mol)
- Electric Current: ampere (A)
Supplementary units: radian [rad] for plane angle and steradian [sr] for solid angle.
2. Important Scientific Instruments
| Instrument | Use / Function |
|---|---|
| Altimeter | Measures altitudes (used in aircraft) |
| Anemometer | Measures force and velocity of wind and directions |
| Barometer | Measures atmospheric pressure |
| Dynamo | To convert mechanical energy into electrical energy |
| Fathometer | Measures depth of the ocean |
| Galvanometer | Measures electric current |
| Hygrometer | Measures level of humidity |
| Lactometer | Measures the relative density of milk to determine purity |
| Seismograph | Measures earthquake intensity |
| Sphygmomanometer | Measures blood pressure |
3. Inventions & Discoveries in Physics
Key Inventions
- Aeroplane: Wright brothers (USA, 1903)
- Barometer: E. Torricelli (Italy, 1644)
- Cinematograph: Thomas Alva Edison (USA, 1891)
- Printing press: J. Gutenberg (Germany, 1455)
- Radar: Dr A.H. Taylor and L.C. Young (USA, 1922)
- Telephone: Alexander Graham Bell (USA, 1876)
- Television: John Logie Baird (Scotland, 1926)
- X-ray: Wilhelm Roentgen (Germany, 1895)
Key Discoveries
- Laws of motion: Newton (1687)
- Atom: John Dalton (1808)
- Electromagnetic Induction: Michael Faraday (1831)
- Radioactivity: Henry Becquerel (1896)
- Electron: J.J. Thomson (1897)
- Photoelectric effect & Relativity: Albert Einstein (1905)
- Proton: Rutherford (1919)
- Neutron: James Chadwick (1932)
4. Conversion of Units
1 Inch = 2.54 centimeter
1 Feet = 0.3 meter
1 Yard = 0.91 meter
1 Mile = 1.60 kilometer
1 Nautical mile = 1.85 kilometer
1 Fathom = 1.8 meter
1 pound = 0.4537 kilogram
1 dyne = 10-5 Newton
1 erg = 10-7 Joule
1 Angstrom = 10-10 meter
1 horse power = 747 Watt
1 square inch = 6.45 sq. centimeter