# Homework Help: Engineering notation question

1. Apr 10, 2013

### marly

I’m taking an electronics course and in the book it’s talking about a period in AC electricity and it asking me to find the frequency for the period and also the time for the frequency.

The problem is this:

Calculate the period for the two frequencies of 1 MHz and 2 MHz.

For 1 MHz I use T = $\frac{1}{f}$ = $\frac{1}{1 x 10^{6}}$ = 1 x 10$^{-6}$ = 1 $\mu$s

This makes sense to me and when I put it in my calculator I get 1 x 10 $^{-6}$

For 2MHz in the book it shows:

For 2 MHz I use T = $\frac{1}{f}$ = $\frac{1}{2 x 10^{6}}$ = .5 x 10$^{-6}$ = .5 $\mu$s

This answer makes sense to me too.

On my calculator it shows 500 x $^{-9}$ which is 500 nanoseconds, instead of .5 microseconds.

What I don't understand, is why would I use .5 $\mu$s instead of 500 nanoseconds?

To me, it would seem more "right" to say, "oh, that's 500 nanoseconds, instead of .5 microseconds".

2. Apr 10, 2013

### SteamKing

Staff Emeritus
3. Apr 10, 2013

### phyzguy

Technically, in engineering notation, the number before the unit should always be between 1.0 and 1000.0. So instead of saying 0.5 microsecond, you should say 500 nanosecond. If you went to shorter and shorter times, you would keep using ns until you got to 1.0 ns, and below that you would say 990 picosecond instead of 0.99 ns. However, there is nothing wrong with saying 0.5 microsecond, and I doubt you would get marked down for giving this answer.

4. Apr 10, 2013

### marly

Thank you very much. That makes sense perfect sense. Thanks!

My book says the answer is .5 microseconds and that’s why I was getting confused. I thought the answer should have been 500 nanoseconds, because as you said, the number before the unit should be 1.0 and 1000.0

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