Units of Conversion (Pulse)

1. Aug 24, 2010

aphotictwil

Time standards are now based on atomic clocks. A promising second standard is based on pulsars, which are rotating neutron stars (highly compact stars consisting only of neutrons). Some rotate at a rate that is highly stable, sending out a radio beacon that sweeps briefly across Earth once with each rotation, like a lighthouse beacon. Suppose a pulsar rotates once every 1.434 806 448 872 75 4 ms, where the trailing 4 indicates the uncertainty in the last decimal place (it does not mean 4 ms).

(c) What is the associated uncertainty of this time?

I attempted to solve the problem find the average between 1.434 806 448 872 79 and 1.434 806 448 872 71 (in seconds, meaning i already divided by 1000m/s) yet I could not get the correct answer.
I also used the answer in part (b) as a base to find the average
That also failed.
I've got the correct answer for (b) but cannot figure out (c)

Heres (b) in case you were interested
b) How much time does the pulsar take to rotate 4.0 106 times? (Give your answer to at least 4 decimal places.)

2. Aug 24, 2010

diazona

Part (c) seems to ask for an associated uncertainty. So what is the definition of associated uncertainty? (It's not an average)

3. Aug 24, 2010

aphotictwil

well i attempted 1.43480644887275/00000000000004
something like that

the problem here i guess is that i don't understand associated uncertainty.
any idea how to solve it/definition is?

4. Aug 25, 2010

diazona

Well, I'm actually not quite sure what it means either. The terms I usually hear are "relative uncertainty" or just "uncertainty", or occasionally "absolute uncertainty".

Maybe the question means "What is the uncertainty associated with this time?" In that case they're just asking for the uncertainty, written out as a time (in milliseconds).

5. Aug 25, 2010

aphotictwil

Its actually very simple

Multiply 4.0x10^6 from (b)
by the uncertainty
(which is .000 000 000 000 04).
That gives you the answer in ms

My final answer required it to be in seconds
so I divided the ans by 1000 m/s

6. Aug 25, 2010

diazona

Ahhh, I see, they were asking for the uncertainty in the answer to part (b). I got thrown off a bit there because you wrote part (c) right after the introductory information.

Anyway, glad you figured it out.