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

Answer:

Difference between base quantities and derived quantities: 

Base quantities:

Base quantities are the quantities on the basis of which other quantities are expressed. There are seven physical quantities that form the foundation for other physical quantities. These physical quantities are called the base quantities.

Examples:

Length, mass, time, electric current, temperature, the intensity of light, and the amount of a substance.


Derived quantities:

Those physical quantities that are expressed in terms of base quantities are called derived quantities.

Examples:

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


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1.3: Pick out the base units in the following: 

joule, Newton, kilogram, hertz, mole, ampere, metre, kelvin, coulomb, and watt.


Answer:

Base units are kilogram, mole, ampere, metre, Kelvin.


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1.4. Find the base quantities involved in each of the following derived quantities: 
(a) speed (b) volume (c) force (d) work


Answer:

(a) speed
Speed = distance covered / time taken
Unit of speed = m / s
Base quantities involved in speed are length and time.


(b) Volume:
Volume = length x width x height
Unit of Volume = m³
The base quantity involved in volume is length.


(c) Force:
Force F = ma
Unit of force = N = kg m s⁻²
Base quantities involved in force are mass, length, and time.


(d) Work:

Work done = Force x displacement
W = F S
Unit of work = J = N m = kg m²s ⁻²
The base quantities involved in work are mass, length, and time.


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1.5. Estimate your age in seconds.

We know that

:: 1 year = 365 days
:: 1 day = 24 Hours
:: 1 hour = 60 Minutes
:: 1 minute = 60 second

Suppose my age = 14 years 
= 14 x 365 = 5110 days 
= 5110 x 24 = 122640 hours 
= 122640 x 60 = 7358400 minutes 
= 7358400 x 60 = 441504000 seconds ----Ans

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1.6.  What role Sl units have played in the development of science?

Answer:
i. SI units are a commonly accepted system of units used all over the world for exchanging all scientific and technical information. 
ii. Manipulation in this system is quite easy i.e. the multiple and sub-multiple of different units are obtained simply by multiplying or dividing with ten or powers of tens.

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1.7. What is meant by Vernier constant?

    Answer:

    Vernier constant is also called Least count (LC): It is the minimum length that can be measured accurately with Vernier Caliper. It is defined as the difference between one main scale division and one Vernier scale division. 

    The least count of the Vernier Calipers can also be found as given below:

    Least count of Vernier Caliper = smallest reading on main scale/number of divisions on Vernier scale 

    LC = 1 mm / 10 divisions
    LC= 0.1 mm = 0.01 cm

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


      Answer:

      Zero Error: 

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

      For Example: To find the zero error of the Vernier caliper, we closed the jaws of the Vernier Calipers gently. If the zero of the Vernier scale coincides with the zero of the main scale then there is NO zero error. 

      Zero error exists when the zero line of the Vernier scale does not coincide with the zero of the main scale. 


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


      Answer:

      Zero error is a defect in the measuring devices (Vernier Calipers & Screw Gauge). So it is necessary to remove the zero error from the final calculation in order to get the correct measurement.


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

      Answer:

      A stopwatch is an instrument used to measure the time interval of an event. There are two types of stopwatches.

      1. Mechanical     2. Digital

      The least count of the mechanical stopwatch used in the laboratories is 0.1 s.

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      1.11. Why do we need to measure extremely small intervals of time?

        Answer:
        To get measurement more precise we need an instantaneous time rate of change of variable which describes how fast the relationship between two variables changes at a particular point. Therefore we need to measure extremely small intervals of time.


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

          Answer:
          All the accurately known digits and the first doubtful digits in an expression are called significant figures. 

          Significant figures = All the accurate + the first doubtful digit

          Example = 32.8 (32 are the accurate + .8 is the first doubtful digit)


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

            Answer:
            The significant figures are all the digits that are known accurately and the one estimated digit. It reflects the precision of a measured value of a physical quantity i.e. more significant figure means greater precision.


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