Physics questions!

[Hutchoo]

Heyah guys
I'm doing some physics questions and I don't understand this one.

When water runs through a hose at the rate of 0.5 litre per second, it can be calculated that electrons pass any point in the hose each second.

Question:
What electric current (in amps) does this represent?

Thanks.

[pi]

Totally forgot this stuff...

Here are some hints though:
- I = Q/t, where I is current (A), Q is charge (C) and t is time (s)
- The charge of an electron is 1.602 × 10^-19 C
- The question has nothing to do with volume, so ignore 'litres'

[Hutchoo]

Thanks Rohitpi... but this is still confusing me.
I don't understand what 1.7x10^26 has to do with finding the electric current in the equation.

[xZero]

Im pretty sure its I=nQ/t, where n = number of electrons

[pi]

Thanks Rohitpi... but this is still confusing me.
I don't understand what 1.7x10^26 has to do with finding the electric current in the equation.

Thats the number of electrons. To find the total charge times 1.7x10^26 with the charge of an electron (1.602 × 10^-19 C).

Then apply I=Q/t.


Pretty sure thats right (haven't done this stuff for about a year)

Im pretty sure its I=nQ/t, where n = number of electrons

I've never heard of that before...

[Hutchoo]

Alright..
So I'll have a go on here and can you guys tell me where I go wrong?
The answer is 2.7 × 10^7.

I=Q/t
1.7x10^26 x 1.602x10^-19 = Q.
Q = 27234000
t= 0.5.
I= 27234000/0.5 = 54468000.

Obviously it's wrong... ARGH. I don't know what I'm doing wrong :s

[pi]

I think t=1, not 0.5 (forget litres, it says 'per second' in the latter part of the question)

The answer is still ridiculously large, so I think scientific notation to 2 sig figs (remember 1.7... has 2 sf) will have to be done too (hence, the answer 2.7x10^7 A, remember units!)


Hopefully I'm right.

[Hutchoo]

Oh, dude... T_T
Thanks >.>
It said 1/2 a litre.. and i thought that was the time LOL.

Thanks
I'll post more up if i'm confused.

[pi]

It said 1/2 a litre.. and i thought that was the time LOL.

To be honest, so did I the first time I read it... Its just out there to trick people, always read the question twice.

Thanks

Thanks to this question, I now remember all this stuff again!

[xZero]

adding n where n = number of w/e to an equation is used on exams and such  so just remember when your given a certain number of something (wires, electrons etc) just try adding the n to the equation

eg for magnetic flux in sem2 and the electron question like this 1

[Hutchoo]

Oh gosh...
The dome on a fully charged Van de Graaff machine may carry something of the order of 50 million million extra electrons. When running well it may take about 3 s to charge up. If we assume no loss of charge in this time, what is the current flowing up the belt to the dome?

I took a look at the answer.. and it has a symbol I've never used before.

THIS IS SERIOUSLY CONFUSING  :uglystupid2:

[Mint]

Microamps! Im probably wrong..

[Cthulhu]

is a greek letter and is used to represent micro-whatevers which is a millionth of whatevers.

[Hutchoo]

Thanks for telling me what the symbol for micro was I didn't know.
Also, how would you show workings for that question 0.o?

[Whatlol]

 the charge on one electron is  1.60217733 × 10-19 (the number of electrons in one culoumb is the inverse of this)

Number of culoumbs = 1.60217733 × 10-19 x 50 x10^12 = 8.01x10^-6 C

I = Q/t

8.01x10^-6 / 3   = 2.67x10^-6 A

 to one sig figure which gives you 3 x10^-6 A