ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: Tea.bag on July 31, 2008, 09:58:08 pm

Title: Electricity
Post by: Tea.bag on July 31, 2008, 09:58:08 pm: Help!

An AC voltmeter is used to measure the voltage between pairs of pins in a power point.
a)with the power point switch off, what would be the voltage between
i)the active and the neutral wires
ii) the active and the earth
iii)the neutral and the earth

b) what would be the voltage in (a) above if the switch was on?
Title: Re: Electricity
Post by: cara.mel on August 01, 2008, 10:24:11 am: This isn't assessable.

I think at the start they are all 0V, and at the end active = 240V (rms), neutral + earth = 0V
But then, I have 0 practical knowledge
Title: Re: Electricity
Post by: gfb on August 20, 2008, 05:29:50 pm: Hi guys, I have a question too :).

(http://img112.imageshack.us/img112/7789/questionsor0.jpg)

I don't understand Q1 :(

..
thanks
Title: Re: Electricity
Post by: /0 on August 20, 2008, 06:12:17 pm: Well... generally if you connect things in parallel then the equivalent resistance will be less than if you connect them in series. I'm not sure if the actual dimensions of the copper wire plays a part but I don't think it should matter. If you want to give a numerical answer use:
$\frac{1}{R_{eq,parallel}}=\frac{1}{0.001}+\frac{1}{100}$
$R_{eq,series} = 0.001+100$
And don't forget the $\Omega$ unit.
Title: Re: Electricity
Post by: Mao on August 20, 2008, 06:18:29 pm: in series: it will have little effect (almost none). the effective resistance will still be about 100 ohms

in parallel: it will significantly reduce the effective resistance (almost to zero). This is because connecting it in parallel provides the current with an alternative low resistance pathway (which it prefers) ==> most of the current flows through the copper wire.
Title: Re: Electricity
Post by: gfb on August 20, 2008, 06:18:39 pm: Thanks DivideBy0 , I've proved it numerically, but just couldn't find a proper explanation for it :D.

Thank you Mao :)
Title: Re: Electricity
Post by: perfectscore on August 20, 2008, 09:08:12 pm: are we expected to know both these questions for unit 4 exam?
Title: Re: Electricity
Post by: cara.mel on August 21, 2008, 08:27:00 am: To clarify:
The length of the wire doesn't matter. They've told you the resistance for that specific bit of 30mm* 0.8mm wire. If it changed (eg got longer), then you'd need to worry about it