 # Class 11 Physics Notes Units And Measurements Chapter 2

## What are units and measurements?

Units and measurement which is given in class 11 physics textbook offer basic knowledge about how the quantities are measured and the types of units that are used with them.

To get more details on Standard Measurement Units, visit here.

### What is the system of units?

Some of the common systems of units that are used in physics are:

• CGS system
• FPS system
• MKS system
• SI system

### What is known as the fundamental quantity?

Certain quantities have been chosen as fundamental quantities because physics is considered to be quantitative science. They are:

• Length
• Mass
• Time
• Electric Current
• Thermodynamic Temperature
• Amount of Substance
• Luminous Intensity

### What is SI unit?

The term stands for International System of Units which has regulated seven base units to be used to represent quantity around the world. These units are:

• Metre
• Kilogram
• Second
• Ampere
• Kelvin
• Mole
• Candela

To get more details on SI unit, visit here.

### Important Questions

1. Provide an Explanation for this statement:
“To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a
standard for comparison”. Reframe the following statements, in view of this :
(a) atoms are small structures
(b) a jet plane travels with a maximum speed
(c) Jupiter’s mass is very large
(d) the air contains a large number of molecules
(e) a proton massive than an electron
(f) the speed of sound is smaller than the speed of light.
1. Let’s suppose a unit of length is chosen such that the speed of light in the vacuum is unity. What will be the distance and displacement between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 s to cover this distance?
1. Which is the most precise device for measuring length :
(a) vernier calipers with 20 divisions on the sliding scale?
(b) a screw gauge of pitch 1 mm and 100 divisions on the circular scale?
(c) an optical instrument that can measure length to within a wavelength of light?

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## Frequently asked Questions on CBSE Class 11 Physics Notes Chapter 2: Unit Measurements

### What is a ‘Unit of measurement’?

A standard amount of a physical quantity, such as length, mass, energy, etc, specified multiples of which are used to express magnitudes of that physical quantity is called a unit of measurement.

### What is the definition of ‘Speed’?

The ratio of the distance traveled by an object (regardless of its direction) to the time required to travel that distance.

### What is ‘Relative error’?

Relative error: When used as a measure of precision, is the ratio of the absolute error of a measurement to the measurement being taken.