Physical Quantities and Measurement

Physical Quantities and Measurement

Theme

• Measurement involves a number and a unit to describe a physical quantity.
• Units are universally accepted and used to communicate scientific information without ambiguities.

Physical Quantities

• Four basic physical quantities: length, mass, time, and temperature.
• Each quantity has its own unit and symbol for representation.

Measurement of Length

• Concept of length: distance between two points.
• Units of length:
  • Metre (m)
  • Submultiples: centimetre (cm), millimetre (mm)
  • Multiples: kilometre (km)
• Devices for measuring length:
  • Metre ruler
  • Measuring tape
• Measurement with a ruler:
  • Readings can be affected by parallax error
  • Correct reading is obtained when the eye is in front of and in line with the reading

Measurement of Mass

• Concept of mass: quantity of matter contained in a body.
• Unit of mass:
  • Kilogram (kg)
  • Submultiples: gram (g), milligram (mg)
  • Multiples: quintal, metric tonne
• Devices for measuring mass:
  • Beam balance
  • Electronic balance
• Measurement with a beam balance:
  • Standard weights are used
  • The total of standard weights gives the mass of the given body

Measurement of Time

• Concept of time: explained in terms of hours, minutes, and seconds.
• Units of time:
  • Second (s)
  • Minutes (min)
  • Hour (h)

Measurement of Temperature

• Concept of temperature: degree of hotness or coldness of a body.
• Unit of temperature:
  • Celsius (°C)
• Devices for measuring temperature:
  • Clinical thermometer
  • Laboratory thermometer

Importance of Measurement

• Measurement is essential in daily life.
• We use instruments or measuring devices to get an exact measurement.

Rules for Units

• Symbols for units are written in small letters.
• Units are never written in plural.
• A space is left between the numerical value and the unit.
• Negative powers are used to express compound units.### Electronic Balance
• The structure of an electronic balance is the load-bearing part that transfers the load of an object to the load cell.
• The load cell converts the load force into electrical signals.
• The signal conditioner is the electronic part that processes the electrical signal and displays the mass.

Measurement of Time

• Time is the interval between two instances or events.
• A solar day is the time taken by the Earth to complete one rotation about its own axis.
• The mean of 365 solar days in a year is called the mean solar day.

Units of Time

• The S.I. unit of time is the second (s), which is defined as 1/86400 part of a mean solar day.
• One second is the time between two consecutive ticks of a pendulum wall clock.
• A minute (min) is a bigger unit of time, with 60 seconds making 1 minute.
• An hour (h) is a still bigger unit of time, with 60 minutes making 1 hour.
• A day is the time taken by the Earth to rotate once on its own axis, which is equal to 24 hours.
• A year is the time taken by the Earth to complete one revolution around the Sun, which is equal to 365 days.

Time Measurement

• A pendulum clock measures time by the time taken for a pendulum to complete one oscillation (2 seconds).
• The clock has a circular dial with 12 markings divided into four quadrants, with 60 small divisions.
• The second's arm moves one small division every second, the minute's arm moves one small division every minute, and the hour's arm moves 5 divisions every hour.

Summary of Time Units

• 1 minute = 60 seconds
• 1 hour = 60 minutes
• 1 day = 24 hours = 24 x 60 x 60 seconds
• 1 year = 365 days = 365 x 24 hours = 3.15 x 10^7 seconds