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

Qualification => IGCSE/ GCSE => Queries => Topic started by: holtadit on October 17, 2009, 07:44:19 am

Title: Physics School Project
Post by: holtadit on October 17, 2009, 07:44:19 am: I am doing a small project for physics this year on the variation of current with voltage of a metallic conductor.

Now all i want to know is the following:

How to calculate the current flowing through a 0.1m long wire of Silver which has a cross sectional area of 0.001 m2. Hence what is the resistance.

The same as above for Gold, Copper, Lead and Aluminium.

Please include the answers with relevant equations. Im doing IGCSEs by the way.
Title: Re: Physics School Project
Post by: wassup on October 17, 2009, 08:39:31 am: I don't think u can calculate this because u need resistivity for this, then only u can find the resistance n then d current.
The first formula will be R=pl/A (Resistivity*Length/Area), then I=V/R. But u don't know the resistivity(p).
Title: Re: Physics School Project
Post by: holtadit on October 17, 2009, 08:42:25 am: http://en.wikipedia.org/wiki/Resistivity
here is the required resistivity values u need. Plz help me!!!!!
Title: Re: Physics School Project
Post by: astarmathsandphysics on October 17, 2009, 08:57:14 am: I will answer when i get home
Title: Re: Physics School Project
Post by: holtadit on October 17, 2009, 09:03:21 am: By the way astar when i used the formulas given i got the following answer for current 15094339.62 amps. It looks wrong... so whats your advice ??

Please do include the units for each value.
Title: Re: Physics School Project
Post by: Ghost Of Highbury on October 17, 2009, 09:10:41 am: i am extremely curious to know how did u find out the cross-sectional area of the wire..(it is so thin!)

ohk,,

plz reply with the values u took

for

length of the wire - ?
and

cross-section area of the silver wire - ?

------------------

also the voltage u used .
Title: Re: Physics School Project
Post by: holtadit on October 17, 2009, 09:20:59 am: Quote
i am extremely curious to know how did u find out the cross-sectional area of the wire..(it is so thin!)

ohk,,

plz reply with the values u took

for

length of the wire - ?
and

cross-section area of the silver wire - ?

I made up the values for cross sectional area and length.... ;D

If u need to change around any of the values voltage, area or length to make it more logical then please do so.

My teacher didnt give us any values nor did we do an actual experiment, yet im supposed to do the project. So i made the values up....
Title: Re: Physics School Project
Post by: Ghost Of Highbury on October 17, 2009, 09:24:20 am: Quote from: Ari Ben Canan on October 17, 2009, 09:20:59 am
I made up the values for cross sectional area and length.... ;D

If u need to change around any of the values voltage, area or length to make it more logical then please do so.

hope ur estimation for the area is close..

and yea...dont make up values for length...its not cumbersome to measure it with a meter rule...

yea...so what values did u take for the current value u posted recently i.e 15094339.62
Title: Re: Physics School Project
Post by: holtadit on October 17, 2009, 09:29:19 am: the ones i posted in the first post.... once again none of these values have been tried out experimentally so please modify if required
Title: Re: Physics School Project
Post by: astarmathsandphysics on October 17, 2009, 09:55:20 am: Definitely wrong. Did you change to metres
Title: Re: Physics School Project
Post by: holtadit on October 17, 2009, 02:06:10 pm: okay i did the following

I multiplied (1.59*10^-8) by 0.1m which is my made up length. I got (1.59*10^-9) which I divided by 0.001m^2 which is my cross-sectional area.

I got 1.59*10^-6 i.e. RESISTANCE

Using V/R=I to calculate current (24V battery) i did 24/(1.59*10^-6) to get 15094339.62 amps for current.
--------------------------------------------------------------------------------------------------------------
So using the area of wire = 0.001 m2 (or any other value to make things more logical)
the resistivity of silver = 1.59*10^-8 (as on wikipedia)
the length of wire = 0.1 m (or any other value to make things more logical)
---------------------------------------------------------------------------------------------------------------
Please calculate the resistance of the wire (using the parameter given) and hence the current flowing through it if 24 V supply is provided.
Title: WOAH!!!! TAKE A LOOK AT PAMELA ANDERSON IN THIS PICTURE !!
Post by: holtadit on October 17, 2009, 02:38:06 pm: I guess no one is interested in my above posts anymore :'( :'(
Title: Re: Physics School Project
Post by: astarmathsandphysics on October 17, 2009, 02:40:17 pm: .001m2 for a wire is massive. Like 3cm by 3cm. I think you should have divided by 1000^2. That only puts you out by a factor of 1000 though. There is another mistake. I will look when i get home.
Title: Re: Physics School Project
Post by: holtadit on October 17, 2009, 02:47:20 pm: Quote
I think you should have divided by 1000^2

Maybe that was a typo by you but if i divide by 1000^2 i get 1.509433962*10^16 amps :-\
Title: Re: Physics School Project
Post by: astarmathsandphysics on October 17, 2009, 05:00:45 pm: Assume wire is 1mm^2 =10^-06m^2
the resistivity of silver = 1.59*10^-8 (as on wikipedia)
the length of wire = 0.1 m (or any other value to make things more logical)
R=pl/A=1.59^10-8 *0.1/10^-6=1.59*10^-3 ohms
I=V/R=24/1.59*10^-3 =15000 Amps
Title: Re: Physics School Project
Post by: holtadit on October 18, 2009, 01:45:18 pm: astar is it really possible to have such a high value for resistance ? are u sure this is correct ?
Title: Re: Physics School Project
Post by: astarmathsandphysics on October 18, 2009, 01:51:23 pm: I corrected my post. Should read amps.
Title: Re: Physics School Project
Post by: holtadit on October 18, 2009, 01:59:25 pm: astar,

Thank you very much for the explanation; it was clear and concise. I now understand something very complex (and outside of my syllabus) thanks to you ;D

Once again thank you ! Now i must finish my project.... :P
Title: Re: Physics School Project
Post by: astarmathsandphysics on October 18, 2009, 03:33:06 pm: Keep me informed