UNIT 1:

Physical Quantities and measurements

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

Ans. The base quantities are defined as themselves, where as derived quantities are defined by the help of two or more base quantities.
Examples of base quantities:

• Time
• Electric current
• Mass

Examples of derived quantities:
• Velocity
• Force
• Acceleration

• Q. Pick out the base units in the following:
  juole, Newton, kilogram, hertz, mole, ampere, meter, kelvin, coulomb and watt.

Ans. Base Quantities:


• kilogram
• mole
• ampere
• meter
• kelvin

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

Ans.

• Speed is distance covered per unit volume. i.e.
  
  so in speed base quantities involved are Length and Time (= ms^-1)



• Volume = Length (m) x width (m) x height (m)
  so the base quantity in volume involved is length only (m³)



• Force: We know that,
  
  so the base quantities involved in force are mass of the object, length and time (kgms^-2)



• Work: We know that,
  
  
  
  so the base quantities involved in work are mass of the object, length and time (kgms^-2 )(m)








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• Q. Estimate your age in seconds.

Ans. Suppose a student is 15 years old.

• Age = 15 years
• Age in months = 15 x 12 = 180 months
• Age in days = 180 x 30 = 5400 days
• Age in hours = 5400 x 24 = 129600 hours
• Age in minutes = 129600 x 60 = 7776000 minutes
• Age in seconds = 7776000 x 60 = 466560000 seconds

OR...

• Age in Seconds = 15 x 12 x 30 x 24 x 60 x 60 = 466560000 seconds

• Q. What role SI units have played in the development of science?

Ans. With the development of science and technology, in the field of science the need for acceptable system of units was felt all over the world particularly to exchange scientific and technical information. So in 1960 international Bureau of weight and measurements decided to introduce worldwide system of measurements that is called international system of units and is commonly written as SI.

• Q. What is meant by vernier constant?

Ans. the difference between one main scale division and one vernier scale division is called vernier constant or least count. i.e. 1mm - 0.9mm = 0.1mm

• Q. What do you understant by the zero error of a measuring instrument?

Ans. in measuring instruments there may be systematic error, due to which a measurement nay be less or greater than actual measurement.

• Q. Why is the use of zero eror necessaty in a measuring instrument?

Ans. Since zero error of instrument effect all the measurements, so it must be necessary we have to take the zero error in any measurement.

• Q. What is stop watch? What is the least count of a mechanical stopwatch you have used in the laboratory?

Ans. A stop watch is used to measure time interval of an event. The mechanical stopwatch has least count 0.1 second.

• Q. Why so we need to measure extremely small interval of time?

Ans. To measure perfect accuracy we need to measure small interval of time.

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

Ans. In any measurement, greater the number of significant figures, grearter is precision.