**Q.1: What is measurement? What is the importance of measurement?**

**Ans: MEASUREMENT:**

The meaning of measurement is the comparison of an unknown quantity with a standard, see how many times it is big or small as compared to the standard.

**importance Of Measurement:**

In our daily life we get knowledge of things through our five senses, touch, smell, taste, sight and hearing. However our sense often do not provide us with correct information.

We use measuring devices generally called apparatus to get the correct measurement. To measure volume we use a measuring cylinder. For mass, we use a common balance and for the measurement of length a meter scale is used. A vernier caliper can measure correctly up to 0.1 mm and a micrometer screw gauge can measure correctly up to 0.1mm. Any instrument whose calibration is in doubt must be checked or discarded.

**Q.2: Define physical quantities? Write down Its types?**

**Ans: PHYSICAL QUANTITIES:**

Every material object has certain characteristics. These are to be measured to specify them. For instance if we want to specify the characteristics of a brick we will have to measure its length, width, height and mass. Such characteristics are called physical quantities

**Types OF PHYSICAL QUANTITIES:**

Scientists have divided all physical quantities into two groups.

- Fundamental quantities
- Derived quantities

**Fundamental Quantities:**

Fundamental quantities length, mass and time are supposed to be the main physical quantities. All physical quantities in mechanics can be expressed in the terms of fundamental quantities.

**Derived Quantities:**

The physical quantities that are derived from fundamental quantities are called derived quantities. The derived quantities are obtained from simple multiplication and division of fundamental quantities.

**Q:what is a system of units? How many systems of units are there?**

Ans: a set of fundamental and derived units is called a systems of unit.

**Types OF System OF UNITS:**

There are four system of units being used in scientific work.

**M.K.S System:**

In MKS system length, mass, and time are fundamental quantities and their units are meter, kilogram and second.

**C.G.S System:**

In CGS system, the fundamental quantities are length, mass and time and their units are in this system are centimeter, gram and second.

**F.P.S System:**

In FPS system, the fundamental quantities are, length, force arid time and their units are in this system are foot, pound, and second. It is also call British Engineering System.

**Basic S.I. Units:**

In S.l. units seven quantities are taken as fundamental quantities which are:

- Length
- Mass
- Time
- Current
- Temperature
- Luminous intensity
- Amount of substance

**Q.15: What are significant figures or digits in a number or reading? What
are the rules for determining significant figures in a number?**

**Ans: NUMBER OF SIGNIFICANT FIGURES IN A NUMBER OR READING:**

If any measurement the accurately known digits and the first doubtful digit are calledsignificant figures of that number.

- Rules for determining significant figures of a number:
- All non- zero digits are significant e.g. 123 has three significant figures 1, 2 and 3.
- Zero appearing between non – zero digits are significant e.g. 7003, 40.71 and 2.503 all have four significant figures.
- Zero appearing in front of all non – zero digits are not significant. They are acting as place holder. e.g. 0.0081, 0.56, 0.00033 all have two significant figures,
- Zeros at the end of a number and to the right of a decimal point are significant e.g. 65.00, 2.010, 7.000 all have four significant figures.
- Zero at the end of a number and to the left of the decimal point (number greater than
- can be confusing. They are not significant if they just serve as place makes to show the magnitude of the number. The zero in 300, 900 and 2821 are probably not significant but some of them may be. We can not tell any difference. If these zeros are measured than they are significant. To avoid ambiguity the measurement should then be written in standard exponential form (scientific) 3.00 x 102,7.00 x 103 and 2.7210 x In these examples the numbers of significant figures are three, four and five respectively.

**Q.16: What Is scientific notation?**

**Ans: SCIENTIFIC NOTATION:**

Scientists often work with very large and very small measurement for example the mass of the earth is about 6,000,000,000,000,000,000,000,000 kg. In this form the measurement take up much space and are difficult to use in calculation. To work with such measurement more easily we can write them in a shortened form by expressing decimal places as powers of ten. This method of expressing numbers is called exponential notation. Scientific notation is based on exponential notation. In scientific notation the numerical part of a measurement is expressed as the product of a number between 1 and 10 and whole number power of ten.

M x 10″

In this expression 1 < M < 10 and n is an integer. For example two kilometers can be expressed as 2 x 10’m.