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A microsecond is an SI unit of time equal to one millionth (10^-6) of a second. Its symbol is µs.

A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond. Because the next SI unit is 1000 times larger, measurements of 10^-5 and 10^-4 seconds are typically expressed as tens or hundreds of microseconds. Some notable examples of times in this range include:

• 1 microsecond (1 μs) – cycle time for frequency 1 x 10⁶ hertz (1 MHz), the inverse unit. This corresponds to radio wavelength 300 m (AM mediumwave band), as can be calculated by multiplying 1 µs by the speed of light (approximately 3×10⁸ m/s) to determine the distance travelled.
• 1 microsecond – the length of time of a high-speed, commercial strobe light flash
• 2 microseconds – the life time of a muonium particle
• 2.68 microseconds – the amount of time subtracted from the Earth Day as a result of the 2004 Indian Ocean earthquake.
• 3.33564095 microseconds – the time taken by light to travel one kilometer in a vacuum
• 4.63 microseconds – a fifth (a 60th of a 60th of a 60th of a second)
• 5.4 microseconds – the time taken by light to travel one mile in a vacuum
• 10 microseconds (μs) – cycle time for frequency 100 kHz, radio wavelength 3 km
• 20.8 microseconds – sampling interval for digital audio with 48000 samples/s
• 22.7 microseconds – sampling interval for CD audio (44100 samples/s)
• 38 microseconds – discrepancy in GPS satellite time (compensated by clock speed) due to relativity
• 50 microseconds – cycle time for highest human-audible tone (20 kHz)
• 100 microseconds (0.1 ms) – cycle time for frequency 10 kHz
• 125 microseconds – sampling interval for telephone audio (8000 samples/s)
• 240 microseconds – half-life of ununbium 277
• 250 microseconds – cycle time for highest tone in telephone audio (4 kHz)
• 277.8 microseconds - a fourth (a 60th of a 60th of a second), used in astronomical calculations by al-Biruni and Roger Bacon in 1000 and 1267 AD, respectively.^[1][2]

[edit] References

1. ^ al-Biruni (1879). The chronology of ancient nations: an English version of the Arabic text of the Athâr-ul-Bâkiya of Albîrûnî, or "Vestiges of the Past". W.H. Allen. pp. 147–149. OCLC 9986841. http://books.google.com/books?id=pFIEAAAAIAAJ&pg=PA148&vq=thirds&lr=. 
2. ^ R Bacon (2000) [1928]. The Opus Majus of Roger Bacon. University of Pennsylvania Press. table facing page 231. ISBN 9781855068568. 

v • d • e Orders of magnitude (time), by powers of seconds Negative powers 10−44 s | ... | 10−24 s ... 10−19 s | 10−18 s ... 10−16 s | 10−15 s ... 10−13 s | 10−12 s ... 10−10 s | 10−9 s ... 10−7 s | 10−6 s ... 10−4 s | 10−3 s | 10−2 s | 10−1 s Positive powers 100 s | 10 s | 102 s | 103 s | 104 s | 105 s | 106 s | 107 s | 108 s | 109 s | 1010 s | 1011 s | 1012 s | 1013 s |1014 s | 1015 s | 1016 s | 1017 s | 1 E18 s and longer