IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: godfather93 on February 13, 2010, 10:42:45 am

Title: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 13, 2010, 10:42:45 am
CAN SOMEONE PLEASE EXPLAIN WHY SOME TERMS ARE NEGLECTED WHEN SOME FORMULAS ARE DERIVED? ISN'T ACCURACY LOST IN DOIN SO?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 13, 2010, 11:07:03 am
ANYONE? ASTAR?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: Saladin on February 13, 2010, 11:42:36 am
Stop writing in caps,

and the answer to ur q is that some quantities can be expressed in others.

So a complicated formula, will have many derived values.
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 13, 2010, 01:26:06 pm
Stop writing in caps,

and the answer to ur q is that some quantities can be expressed in others.

So a complicated formula, will have many derived values.

thanks 4 replying but thats not the answer i am looking 4
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 14, 2010, 03:15:03 am
ALSO can someone tell me the diff By the way +-(plus on top of minus) and -+(minus on top of plus)?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 14, 2010, 04:21:54 am
the symbol ?, meaning "minus or plus", used alongside the plus-minus sign to show that a negative value is to be taken where the positive value is indicated by the plus-minus sign, and vice versa (as in (x ± 1) / (x ? 2), which means (x + 1) / (x - 2) and (x - 1) / (x + 2)).

Hope that helped :)
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 14, 2010, 11:34:41 am
thanks for that! :D i had the same logic in mind but somehow in formula derivations, it doesn't seem to work that way! :(
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 14, 2010, 07:46:05 pm
put up a sample...I'll check it out
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 15, 2010, 10:24:48 am
i'll put up the sample later.

Right now, I have a more important and tricky question --

Is chemistry as a subject a completely  theoretical subject???

U may think as to why i'm asking that but have u ever wondered, for example, why the number of electrons in the outermost shell is 8? I mean there is no clear cut evidence saying so, is there?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 15, 2010, 12:09:32 pm
Yes there is and it's a lil difficult to explain....
Check http://www.knockhardy.org.uk/ppoints.htm - electronic configuration
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 15, 2010, 12:14:36 pm
ok here's another question. We've all being studying electricity. But can u answer this simple question -

Before the discovery of electrons, how were the terminals of the battery marked as positive and negative?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 15, 2010, 12:22:32 pm
moreover, i would like to know that if u guyz have learnt the quantum theory, are we supposed to just memorize the postulates and rules or is there any background info given to u on how the scientists discovered it?

sorry that i have loads of questions! :-[
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 15, 2010, 12:38:43 pm
According to the atomic theory, atoms are moving all the time, but to different extents in solids, liquids and gases. if we accept the theory, the question is why can't we see the motion of atoms in a liquid i.e why does it seem to be standing still when all the molecules are constantly moving here and there?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 15, 2010, 12:48:59 pm
ok here's another question. We've all being studying electricity. But can u answer this simple question -

Before the discovery of electrons, how were the terminals of the battery marked as positive and negative?

when were batteries invented??:P
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 15, 2010, 12:50:32 pm
1800, by Allesandro volta
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 16, 2010, 11:59:14 am
can someone tell me what scalar and vector product is??
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 16, 2010, 12:01:34 pm
U mean product of a scalar and vector??
Product should be a vector
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 16, 2010, 12:02:44 pm
no no not that. Haven't u studied the product of 2 vector quantities?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 16, 2010, 12:06:35 pm
no no not that. Haven't u studied the product of 2 vector quantities?

Are you talking about vector quantities literally or are u referring to vectors in terms of i,j,k??
Could you post an example sort of..
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 16, 2010, 12:13:21 pm
http://en.wikipedia.org/wiki/Cross_product
http://en.wikipedia.org/wiki/Dot_product

the above two links show the 2 ways of multiplying vectors (and ofcourse vector quantities)!!
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 16, 2010, 12:42:22 pm
I thought u were asking about physical quantities...like velocity,displacement :|
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 16, 2010, 12:46:16 pm
yes physical quantities are involved as well.

Ex. work done = vector F . vector S = F.S.cos x where x is the angle between the 2 vectors F(force) and S(displacement).
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 16, 2010, 12:48:10 pm
So what is your question...
You knw how to multiply vectors don't ya?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 16, 2010, 12:49:00 pm
Actually my question is do u know why vectors can be multiplied in 2 ways to get 2 different answers? it's a hard q, i know.
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: nid404 on February 16, 2010, 12:51:30 pm
Actually my question is do u know why vectors can be multiplied in 2 ways to get 2 different answers? it's a hard q, i know.

woopsy...nope...but ill try n find out
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: godfather93 on February 16, 2010, 12:53:54 pm
By the way, have u studied about vector multiplication (vector x vector)?
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: astarmathsandphysics on February 16, 2010, 03:54:28 pm
Will do a page on vector and scalar products.
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: astarmathsandphysics on February 16, 2010, 11:31:31 pm
http://www.astarmathsandphysics.com/a_level_maths_notes/a_level_maths_notes_fp4_menu.html
Title: Re: PHYSICS, CHEM HELP NEEDED
Post by: tarifhossain on February 17, 2010, 07:24:51 am
Thank you very much for the papers.