Units & Measurements
Introduction to Units & Measurements
Measurement is the foundation of physical science. In competitive exams, the focus is on the SI (System International) units, common Derived Units, and the metric prefixes used to scale them.
Classification: Types of Units
- SI Base Units: The seven fundamental units that form the building blocks of all measurement.
- Derived Units: Units created by mathematically combining base units (e.g., Force, Pressure, Power).
- Practical Units: Units used in specific industries (e.g., Horsepower in engineering, Light Year in astronomy).
The Units & Measurements Master Table
| Quantity | SI Unit | Symbol | Category |
|---|---|---|---|
| Mass | Kilogram | kg | Base Unit |
| Temperature | Kelvin | K | Base Unit |
| Luminous Intensity | Candela | cd | Base Unit |
| Force | Newton | N | Derived (kg·m/s²) |
| Pressure | Pascal | Pa | Derived (N/m²) |
| Work / Energy | Joule | J | Derived (N·m) |
| Power | Watt | W | Derived (J/s) |
| Frequency | Hertz | Hz | Derived (1/s) |
Key Scientific Facts
- The Kelvin Scale starts at absolute zero, the theoretical point where all molecular motion stops.
- One Horsepower is numerically equal to exactly 746 Watts.
- A Light Year is a unit of distance, not time, representing how far light travels in one year (~9.46 trillion km).
- The Decibel (dB) is the logarithmic unit used to measure the intensity (loudness) of sound.
- Mach Number is used to represent the speed of an object relative to the speed of sound.
Subject Card Prompts (Flashcards)
- Q: What is the SI unit of Electric Current?
- A: Ampere (A).
- Q: Which unit is used to measure the depth of the ocean?
- A: Fathometer (expressed in Fathoms).
- Q: One 'Knot' is a unit of speed used in which field?
- A: Navigation and Aviation (Nautical miles per hour).
- Q: What is the SI unit of "Amount of Substance"?
- A: Mole (mol).
Practice MCQ
"Which of the following is the SI base unit for Temperature?"
A) Celsius
B) Fahrenheit
C) Kelvin
D) Joule
(Correct: C - Kelvin)