CIE AS Physics (9702) 2019-2021

Revision Notes

1.1.3 Homogeneity of Physical Equations

Homogeneity of Physical Equations

  • An important skill is to be able to check the homogeneity of physical equations using the SI base units
  • The units on either side of the equation should be the same
  • To check the homogeneity of physical equations:
    • Check the units on both sides of an equation
    • Determine if they are equal
    • If they do not match, the equation will need to be adjusted


Homogeneity of Physical Equations, downloadable AS & A Level Physics revision notes

How to check the homogeneity of physical equations

Powers of Ten

  • Physical quantities can span a huge range of values
  • For example, the diameter of an atom is about 10–10 m (0.0000000001 m), whereas the width of a galaxy may be about 1021 m (1000000000000000000000 m)
  • This is a difference of 31 powers of ten
  • Powers of ten are numbers that can be achieved by multiplying 10 times itself
  • It is useful to know the prefixes for certain powers of ten

          Powers of Ten Table

1.1.2 Powers of Ten Table

Exam Tip

You will often see very large or very small numbers categorised by powers of ten, so it is very important you become familiar with these as getting these prefixes wrong is a very common exam mistake!

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