Federal Board, FBISE Class 9 Physics Notes of Chapter 1 Exercise are given below. All the excise questions are solved.

## Chapter 1 Exercise

### Short questions

**1.2 What is difference between base quantities and derived quantities? Give three examples in each case.**

Ans.

Base Quantities | Derived Quantities |

Base quantities are the quantities on the basis of which other quantities are expressed. | The quantities that are expressed in terms of base quantities are called derived quantities. |

Examples: length, mass, time | Examples: area, volume, speed |

**1.3 Pick out the base units in the following:** joule, newton, kilogram, hertz, mole, ampere, metre, kelvin, coulomb, and watt.

**Ans.** The base units are kilogram, mole, ampere, meter, kelvin.

**1.4** **Find the base quantities involved in each of the following derived quantities: ** **(a) Speed (b) Volume (c) Force (d) Work**

**1.5 Estimate your age in seconds. **

Ans.Suppose my age is 14 years. So 14 years = 14 × 365 days = 5110 days (∴1 year = 365 days) = 5110×24 hours =122640 hours (∴1 day = 24 hours) = 122640 ×60 minutes=7358400 minutes (∴1 hour = 60 minutes) = 7358400 ×60 seconds=441504000 seconds (∴1 minute = 60 seconds) 14 years =441501000 seconds =4.415×10^{8}seconds

**1.6 What role SI units have played in the development of science?**

**Ans.** The SI units have played an important role in the development of science. With the development in the field of science and technology, the need for a commonly accepted system of units was seriously felt all over the world and was introduced as a worldwide system of measurements.

**1.7 What is meant by vernier constant?**

**Ans: Vernier Constant: ** The difference between one small division on the main scale and one division of the Vernier Scale is 0.1 mm. It is called the least count (L.C) of Vernier Calipers or Vernier Constant.

It is calculated as:

**1.8 What do you understand by the zero error of a measuring instrument?**

**Ans. **If the zero line of a measuring instrument does not coincide with the index line. The instrument is said to have a zero error. By knowing the zero error, the reading taken by the instrument can be corrected.

**1.9 Why is the use of zero error necessary in a measuring instrument?**

**Ans. **When making some kind of scientific measurement, it is necessary to first check our instrument for “Zero Error”. The zero error is the reading displayed when we know the true reading should be exactly zero. ** **

** **After finding zero error, we need to apply zero correction to get the correct reading.

**1.10 What is a stopwatch? What is least count of a mechanical stopwatch you have used in labs?**

**Ans.** **Stopwatch:** A stopwatch is used to measure the time interval of an event. There are two types of stopwatches (a) Mechanical stopwatch and (b) Digital stopwatch

The least count of a mechanical stopwatch we have used in the laboratory is 0.1 seconds.

**1.11 Why do we need to measure extremely small interval of times?**

**Ans:** Several incidents occur in a very short interval of time. Therefore we need to measure these intervals. For such intervals, we use sub-multiples of units of time such as microseconds (10-6 s), nanoseconds (10-9 s), and picoseconds (10^{-12} s)

**1.12 What is meant by significant figures of a measurement?**

**Ans. Significant Figures**: All the accurately known digits and the first doubtful digit in an expression are called significant figures.

The following rules are helpful in identifying significant figures:

(i) Non-zero digits are always significant.

(ii) Zeros between two significant figures are also significant.

(iii) Final or ending zeros on the right in the decimal fraction are significant.

(iv) Zeros written on the left side of the decimal point for the purpose of spacing the decimal point are not significant.

(v) In whole numbers that end in one or more zeros without a decimal point. These zeros may or may not be significant. In such a case, express the quantity using scientific notation to find the significant zero.

**1.13 How is precision related to the significant figures in a measured quantity?**

**Ans. **The accuracy in measuring a physical quantity depends upon various factors.

1. The quality of the measuring instrument.

2. The skill of the observer.

3. The number of observations made.

However, the precision of measured quantity is also directly related to the number of significant figures. More significant figures mean greater precision

### Chapter 1 Exercise Class 9 Physics Notes

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