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## Short Type Questions

#### Q.1 What is the difference base quantities and derived quantities? Give three examples in each case.

Ans: Difference between base quantities and derived quantities:

Base quantities:

Base quantities are the quantities based on which other quantities are expressed.

There are seven physical quantities which form the foundation for other physical quantities. These physical quantities are called the base quantities.

Example:

Length, mass, line, electric current, temperature, the intensity of light, and the derived quantities.

Derived quantities:

The quantities that are expressed in terms of base quantities are called derived quantities.

Example:

Area, volume, speed, force, work, energy, power, electric charge, electric potential, etc.

#### Joule, newton, kilogramme, hertz, mole, ampere, metre, kelvin, coulomb and watt.

Ans: Base unit:

kilogramme, mole, ampere, metre, Kelvin.

#### (a)speed                        (b)volume              (c)force                   (d)work

Ans: (a)Speed:

Speed = distance covered / time taken

unit of speed = metre / second = ms^-1

Base quantities involved in speed are metre and second.

(b)Volume:

Volume = length ×width ×height

Volume = m× m× m= m^3

or      Base quantity involved in volume is metre.

(c) Force:

F =ma

1N = 1 kg× 1ms^-2

1N = 1 kgms^-2

(d)Work:

Work done = Force × displacement

W = FS        ……… (i)

1J    =        1N × 1 m

1J    =        1 kgms^-2  × 1 m

1J    =        = 1 kgms^-2

Base quantities involved in work are kilogramme, metre, and second.

#### Q.4 Estimate your age in seconds.

Ans:  Suppose my age = 15 years

=   15 × 365 = 5475days (∴ 1 year = 365 days)

=     5465 × 24 = 131400 hours (∴ 1day = 24hours)

=     131400 × 60 = 7884000 minutes (∴ 1 hour = 60 minutes)

=      7884000× 60 = 473040000 seconds (∴ 1 minutes = 60 second)

#### Q.5 What role SI units played in the development of science?

Ans: i.  SI unit is in use all over the world.

1. Manipulation in this system is quite easy i.e. the multiples and submultiples of the different unit are obtained simply by multiplying or dividing with ten or powers of ten.

#### Q.6 What is meant by Vernier constant?

Ans: Least Count (LC)/ Vernier constant:

The difference between one small division on main scale division and one on Vernier scale division is 0.1 mm. it is called least count (LC) of the Vernier Calipers.

Least count of Vernier Calipers can also be found as given below:

Least count of Vernier Calipers =

=  = 0.1 mm

LC     = 0.1 mm = 0.01 cm

#### Q.7 What do you understand by the zero error of a measuring instrument?

Ans: Zero Error and Zero Correction:

It is a defect in measuring device (Vernier Calipers & Screw Gauge) & zero error is caused by an incorrect position of the zero point

For Example:

To find the zero error, close the jaws of Vernier Calipers gently. If zero line of the Vernier scale coincides with the zero of the main scale then the zero error is zero. Zero error will exist if the zero lines of the Vernier scale is not coinciding with the zero of the main scale.

#### Q.8 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 your instrument for ‘zero error’. The zero error is the reading displayed when you know the true reading should be exactly zero.

For example, using a set of Vernier callipers, the zero is the reading that shows when the callipers are fully closed.

As long as check for zero error, you can then use it to correct your readings.

Positive zero error:

Zero error will be positive if the zero lines of the Vernier scale is on the right side of the zero of the main scale.

To get the correct value zero error must be recorded and subtracted from each reading.

Negative zero error:

Zero error will be negative if the zero lines of the Vernier scale is on the left side of the zero of the main scale.

To get the correct value zero error must be recorded and add to each reading.

#### Q.9 What is a stopwatch? What is the least count of a mechanical stopwatch you have used in the laboratories?

Ans: Stopwatch:

A stopwatch is used to measure the time interval of an event.

Mechanical stopwatch:

A mechanical stopwatch can measure a time interval up to a minimum 0.1 second.

Least count of the mechanical stopwatch is 0.1 second.

Digital stopwatch:

Digital stopwatches commonly used in laboratories can measure a time interval as small as 1/100 second or 0.01 second.

Least count of the digital stopwatch is 0.01 second.

How to use a Stopwatch:

Use of a mechanical stopwatch:

A mechanical stopwatch has a knob that is used to wind the spring that powers the watch. It can also be used as a start-stop and reset button. The watch starts when the knob is pressed once. When pressed the second time, it stops the watch while the third press brings the needle back to zero position.

Use of a digital stopwatch:

The digital stopwatch starts to indicate the time lapsed as the start/stop button is pressed. As soon as the start/stop button is pressed again. It stops and indicates the time interval recorded by it between the start and stop of an event. A reset button restores its initial zero settings.

#### Q.10 Why do we need to measure an extremely small interval of times?

Ans: We need an extremely small interval of time “delta t” (∆t) as the smaller is the time interval better resolution of the measurement is possible.

For example:

In atomic/quantum physics, especially reactions take place in a very short amount of time.

#### Q.11 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. It reflects the precision of a measured value of a physical quantity.

The accuracy in measuring a physical quantity depends upon various factors:

1. The quantity of the measuring instrument
2. The skill of the observer
• The number of observations made

For example, a student measures the length of a book as 18cm using a measuring tape. The numbers of significant figures in his/her measured value are two. The left digit 1 is the accurately known digit. While the digit 8 is the doubtful digit for which the student may not be sure.

Rules for determining significant figures:
The following rules help identify significant figure:

• Non-zero digits are always significant.
• Zeros between two significant figures are also significant.
• Final or ending zeros on the right in the decimal fraction are significant.
• Zeros written on the left side of the decimal point to space the decimal point are not significant.
• In whole numbers that end in one or more zeros without a decimal point. These zeros may or may not be significant. In such cases, it is not clear which zeros serve to locate the position value and which are parts of the measurement. In such a case, express the quantity using scientific notation to find the significant zero.

#### Q.12 How is precision related to the significant figures in a measured quantity?

Ans:  The greater the number of significant figures, the greater the precision. Each significant figure increases the precision by a factor of ten.

An improvement in the quality of measurement by using better instrument increases the significant figures in the measured result. The significant figures are all the digits that are known accurately and the one estimated digit. The more significant figure means greater precision. 