Physics: Units and Measurements

Units and Measurements

• Physics: A physical science studying matter, energy, and their interactions.

Branches of Physics

• Introduction to Physics
• Mechanics
• Thermal Physics
• Electricity and Magnetism
• Waves and Optics
• Modern Physics

Quantities and Units

• Physical Quantities: Measurable parameters in physics.

• Fundamental Quantities: Independent quantities (e.g., mass, length, time).

• Derived Quantities: Dependent quantities, calculated from fundamental ones through multiplication or division (e.g., velocity, force). Do not subtract or add to derive these.

• Fundamental Quantities and Units (7 generally accepted, 5 basic):

  • Mass (kilogram, kg)
  • Length (meter, m)
  • Time (second, s)
  • Thermodynamic temperature (Kelvin, K)
  • Electric current (Ampere, A)
  • Luminous intensity (Candela, cd)
  • Amount of substance (mole, mol)
  • Plane angle (radian, rad)
  • Solid angle (steradian, sr)

• Systems of Units:

  • CGS (centimeter-gram-second)
  • FPS (foot-pound-second)
  • MKS (meter-kilogram-second)
  • SI (International System of Units): A widely used modification of MKS.

• Practical Units: Fundamental or derived units used in specific contexts. Examples of Practical Units include a light year(distance), or horsepower (power).

Measurement of Time

• Time is measured using stopwatches, clocks, and ticker tape timers.
• Accurate clocks include atomic clocks and quartz crystal clocks.
• Sidereal time is used in astronomy.
• Ticker tape timers measure both distance and time simultaneously.

Measurement of Mass

• Mass is the quantity of matter.
• Measured using beam balances or chemical balances, which use the principle of moments.
• Mass is constant and does not change with gravity.

Measurement of Weight

• Weight is the gravitational pull on an object.
• Measured with spring balances, which operate based on Hooke's Law.
• Weight varies with gravity.

Dimensional Formula

• Dimensional formula expresses a physical quantity in terms of fundamental units (M, L, T.).
• Steps to write a dimensional formula:
  1. Write the equation for the physical quantity.
  2. Express all quantities in terms of fundamental quantities.
  3. Replace fundamental quantities with M, L, T.
  4. Indicate powers.

Dimensional Analysis

• Used to:
  1. Verify the dimensional correctness of an equation (principle of homogeneity)
  2. Convert units between systems (e.g., CGS to SI)
  3. Develop relationships between quantities
  4. Determine the dimensions of physical constants from equations

Measurement Instruments

• Meter Rule: Measures length with accuracy to 0.5 mm (0.05 cm).
• Vernier Caliper: Measures length with higher accuracy to 0.1 mm (0.01 cm), typically used for small items like object thickness.
• Micrometer Screw Gauge: Measures very small lengths with accuracy to 0.01 mm (0.001 cm), often used for very thin objects or small diameters.

SI Prefixes

• A table of SI prefixes and their values in powers of 10.