What's the question?

How we would express that verbally in English? Or how to write it?

"to the power of X" = hoch (although shorthand is just "to the Xth")

If it's just the number you want, well it's the same (e.g. 2 E-5 or using superscript for the index, in this case, -5).

so it is: two times minus five to the power of ten?

#2: ?

@noli
no, it's two times ten to the minus five (pa).

I think it's spoken as "two times ten to the minus fifth" or "two times ten to the power of minus five".

Definitely not "to the fifth", as this would mean 2 x 10^(1/5)

if "hoch" = "to the power of"

A hoch B = A to the power of B.
or
A to the Bth.

The rest you really ought to be able to figure out yourself, because the rest is just the maths, not English :P (although people have provided you with the answer on a platter anyway)

@7: totally disagree. "to the xth" is shorthand for "to the Xth power", not "to the power of 1/X".

Thank you, x (#9). That's how we learnt it at school. Two to the fifth, so by analogy two to the minus fifth.
Sorry, #7; you're wrong.

two times ten to the power of negative five

is how I'd say it

Two times ten to the minus fifth. Use the ordinal because of the implied "power." Two times ten to the fifth power. Two times ten squared=two times ten to the second. No one would say two times ten to the two. "To the power of five" is not used. Dude, you asked me recently how my German is. I'd ask you in which language you studied math.

The only way I can think of to express the fractional power in words is: two to the minus one-fifth X (or to the one-fifth power of X--the correct usage of "power of"). But to say it in words, it's easier to rewrite it using whole numbers: two to the minus one-fifth X=one over two to the fifth root of X.

There are lots of sites that explain negative and fractional exponents.

A bit OT, but I'd say:
... twenty micro-Pascals.

I'm not a mathematician, mabr, and my math classes (here in the US) are but a distant memory, but there do seem to be some people who say it the way I said it: http://answers.yahoo.com/question/index?qid=2...
Explain how 3 to the power of negative 2 does not equal negative 9?
3 to the power of negative 2 looks like this in an equation:
-3 x -3. You need to make the 3 negative since the power of 2 is negative. And negative 3 times negative 3 is 9, not negative 9.

Not a mathematician, that's clear. -3 squared is -3x-3=9. 3 to the minus 2=1/3. Google negative exponents, as I say.

Not a mathematician, then. But a good sport. A little ribbing is good from time to time.

And to answer your question, I pass for German in the dark with the light behind me. Recognize the allusion?

Re #4: Steve, you mistook nuki for noli I'm afraid . . . ;-)

Bin Mathematiker.

Meiner Meinung nach müsste es gesprochen "two times ten to the power of minus five" heißen. Das ist gleichbedeutend mit "two divided by ten to the power of five" oder
"two divided by one hundred thousand" oder "two percent of one thousandth" oder in diesem Fall, wie schon wor (#13) bemerkte, "20 micropascal".

... und wie sieht das hier aus:

' 2 x 10-ⁿ' with ' ⁿ' being '5' ? . . .

Was sieht wie aus? Was ich erkenne ist "2 mal 10 hoch -5" und das ist "2 geteilt durch 10 hoch 5".

@ nuki: Was hast du gemeint ? . . .

... und umgangssprachlich ist das 'Unterdruck' . . .

@Daddy ...:
"Unterdruck" ist nur als (negativer) Differenzdruck im Vergleich mit dem Druck in einem Vergleichsraum (z.B. mit dem Atmosphärendruck) definiert. nuki fragte nach einem extrem geringen Druck, wenn man bedenkt, dass Druck üblicherweise in Kilopascal (1000 * Pascal) oder Hektopascal (100 * Pascal) = Millibar angegeben wird.

Von "Unterdruck" ist da keine Rede. Was meinst Du mit "umgangssprachlich"?