Order of magnitude
A rough estimate of the size of a physical quantity expressed as a power of 10. Orders of magnitude allow physicists to make quick estimates and comparisons between vastly different scales without precise calculations. A quantity is said to be 'of the order of' a certain power of 10 when it is comparable to that value.
Real World
Enrico Fermi famously estimated the number of piano tuners in Chicago using only rough powers of 10 — his answer was remarkably close to the real figure, demonstrating the power of order-of-magnitude reasoning.
Exam Focus
Round values to one significant figure and express as powers of 10 — examiners award marks for sensible estimates, not exact figures.
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