SI Units and Physical Quantities List: Base Units, Derived Units, Conversions and Scientists for SSC
Rahul Kumar
SSC Exam Expert & Content Editor
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"What is the SI unit of pressure?" is a sure question in SSC General Science. The SI system has 7 base units and many derived units, and many of them are named after scientists. This SI units and physical quantities guide for SSC gives all of them in tables, with the conversions that are asked in the exam.
Seven SI Base Units
| Quantity | SI unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Important Derived Units
| Quantity | SI unit | Symbol | Meaning |
|---|---|---|---|
| Force | newton | N | kg m/s² |
| Pressure | pascal | Pa | N/m² |
| Work and energy | joule | J | N m |
| Power | watt | W | J/s |
| Frequency | hertz | Hz | 1/s |
| Electric charge | coulomb | C | A s |
| Potential difference | volt | V | J/C |
| Resistance | ohm | Ω | V/A |
| Capacitance | farad | F | C/V |
| Inductance | henry | H | Wb/A |
| Magnetic flux | weber | Wb | V s |
| Magnetic flux density | tesla | T | Wb/m² |
| Conductance | siemens | S | 1/Ω |
| Radioactivity | becquerel | Bq | 1/s |
| Illuminance | lux | lx | lumen/m² |
| Area / Volume | square metre / cubic metre | m² / m³ | |
| Speed / Acceleration | m/s / m/s² | ||
| Density | kg/m³ | ||
| Momentum | kg m/s |
Units Named After Scientists
| Unit | Scientist |
|---|---|
| newton | Isaac Newton |
| joule | James Prescott Joule |
| watt | James Watt |
| pascal | Blaise Pascal |
| hertz | Heinrich Hertz |
| ohm | Georg Ohm |
| volt | Alessandro Volta |
| tesla | Nikola Tesla |
| farad | Michael Faraday |
| henry | Joseph Henry |
| coulomb | Charles-Augustin de Coulomb |
| becquerel | Henri Becquerel |
Useful Conversions
| Conversion | Value |
|---|---|
| 1 horsepower (hp) | 746 watt |
| 1 kilowatt hour (kWh, one unit of electricity) | 3.6 × 10⁶ joule |
| 1 atmosphere | 101,325 pascal |
| 1 bar | 10⁵ pascal |
| 1 calorie | About 4.18 joule |
| 1 electron volt (eV) | 1.6 × 10⁻¹⁹ joule |
| 1 light year | 9.46 × 10¹⁵ metre |
| 1 km/h | 5/18 m/s |
| 1 litre | 1000 cubic cm (10⁻³ cubic m) |
| 1 quintal | 100 kg |
| 1 tonne | 1000 kg |
| 0°C | 273 K |
Solved Examples
Example 1. What is the SI unit of work?
It is the joule.
Example 2. A 100 W bulb is used for 10 hours. How many units of electricity are used?
100 W × 10 h = 1,000 Wh = 1 kWh (1 unit).
Example 3. Convert 36 km/h into m/s.
36 × 5/18 = 10 m/s.
Example 4. Convert 27°C into kelvin.
27 + 273 = 300 K.
Quick Tips
- Learn the 7 base units first.
- Learn the derived units with their formulas (N = kg m/s²).
- Learn the scientists with their units.
- Remember the kWh = 3.6 million joules.
Quick Revision Points
- The 7 SI base units are m, kg, s, A, K, mol and cd.
- The SI unit of force is newton and of pressure is pascal.
- The SI unit of power is watt and of frequency is hertz.
- 1 hp = 746 W.
- 1 kWh = 3.6 × 10⁶ J.
Practice Questions With Answers
- What is the SI unit of force?
Answer: Newton - What is the SI unit of pressure?
Answer: Pascal - What is the SI unit of power?
Answer: Watt - What is the SI unit of frequency?
Answer: Hertz - What is the SI unit of electric current?
Answer: Ampere - How many watts are there in 1 horsepower?
Answer: 746 - How many joules are there in 1 kWh?
Answer: 3.6 × 10⁶ - What is the SI unit of resistance?
Answer: Ohm - What is the SI unit of luminous intensity?
Answer: Candela - What is the SI unit of temperature?
Answer: Kelvin
How to Practise This Chapter
Write each formula on a card, with a solved example on the back, and revise the cards every day. Then test yourself with our practice papers and the previous year papers page. See all guides on the Formula Guide page, and also read the Mathematics notes and Quantitative Aptitude notes. The previous guide is Squares, Cubes and Roots Table and the next guide is AP, GP and Logarithm. Also read the Physics and Chemistry Formula Guide.
Frequently Asked Questions
How many SI base units are there?
There are 7 SI base units.
What is the SI unit of mass?
The kilogram.
What is the SI unit of force?
The newton.
What is the SI unit of energy?
The joule.
What is the SI unit of pressure?
The pascal.
What is the SI unit of power?
The watt.
What is one unit of electricity?
One kilowatt hour (kWh).
How many watts are in 1 horsepower?
746 watts.
What is the SI unit of magnetic flux density?
The tesla.
Is this topic asked in SSC exams?
Yes. SI units are asked in SSC General Science.
How can I learn the units?
Learn them with the formula of the quantity, and in groups.
What is the SI unit of the amount of a substance?
The mole.
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Squares, Cubes, Square Roots and Powers Table: 1 to 30 Squares and 1 to 15 Cubes for SSC Maths
Next chapter
AP, GP and Logarithm Formula Guide: Arithmetic Progression, Geometric Progression and Log Laws for SSC
Rahul Kumar
SSC Exam Expert & Content Editor
Rahul is a senior SSC exam strategist with 8+ years of experience helping aspirants crack CGL, CHSL and MTS exams. He writes in-depth notification breakdowns, exam pattern guides and preparation strategies.