Dimensions of Fundamental Quantities

Unit, Dimensions, and measurements > Dimensions

Dimensions

• The power to which fundamental quantities must be raised in order to express the given physical quantity are called its dimensions.
• To make it more clear, consider the physical quantity force
  Force = mass X acceleration
           
  = mass x velocity/time
  
            = mass x (length/time)/time
            = mass x length x (time)² …(i)
  Thus the dimensions of force are 1 in mass, 1 in length and -2 in time.
  
  Thus equation (i) can be written as [force] = [MLT^-2]

Important dimensions of complete physics

Heat

Electricity

Significant figures

Significant figures in the measured value of a physical quantity tell the number of digits in which we have confidence. Larger the number of significant figures obtained in a measurement, greater is the accuracy of the measurement. The reverse is also true.

• All non-zero digits are significant.
  Example: 64.7 has three significant figures.
• A zero becomes a significant figure if it appears between two non-zero digits.
  Example: 2.98 has three significant figures.
• Leading zeros or the zeros placed to the left to the number are never significant.
  Example: 0.879 has three significant figures.
• Trailing zeroes or the zeroes placed to the right of the number are
  significant.
  Example: 2.270 has four significant figures.
• In exponential notation, the numerical portion gives the number of
  significant figures. Example: 2.24 x 10^-3 has three significant figures.