What are the two essential parts of a measurement?
Answer:
A measurement consists of a numerical value and a unit. A number without a unit does not completely describe a physical quantity.
Question 12
Why is a measurement without a unit meaningless?
Answer:
A numerical value alone does not identify the standard used for comparison. The unit is necessary to understand and compare the measured quantity correctly.
Question 13
What is the International System of Units?
Answer:
The International System of Units is a standardized measurement system based on seven base units. It is abbreviated as SI and is used internationally.
Question 14
Why is the SI system important?
Answer:
The SI system enables scientists and other people worldwide to record, compare and communicate measurements using the same standards. It prevents confusion caused by different local units.
Question 15
Name the seven SI base quantities.
Answer:
The seven SI base quantities are length, mass, time, temperature, electric current, luminous intensity and amount of substance.
Question 16
Write the SI base units of length, mass and time.
Answer:
The SI base unit of length is metre (m), mass is kilogram (kg), and time is second (s).
Question 17
Write the SI base units of temperature and electric current.
Answer:
The SI base unit of temperature is kelvin (K), while the SI base unit of electric current is ampere (A).
Question 18
Write the SI base units of luminous intensity and amount of substance.
Answer:
The SI base unit of luminous intensity is candela (cd), and the SI base unit of amount of substance is mole (mol).
Question 19
What is a derived unit?
Answer:
A derived unit is a unit that can be expressed in terms of SI base units. For example, the unit of speed is m s-1 and the unit of area is m2.
Question 20
How is the SI unit of area derived?
Answer:
Area equals length multiplied by breadth. Therefore, its SI unit is metre multiplied by metre, which is square metre (m2).