ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: SDPHD on April 12, 2011, 10:07:06 am

Title: Electronics Questions!
Post by: SDPHD on April 12, 2011, 10:07:06 am

Hey all,

To put it plainly, I just don't get this question.

(http://i.imgur.com/Al3CS.png)

Any help would be much appreciated.

Title: Re: Electronics Question
Post by: schnappy on April 12, 2011, 02:32:34 pm

This is tricky. I'm not confident enough to give an answer for b), but for a)... 5kOhm is P, 2kOhm is Q. The current will flow to earth as it does, so must be going down through X, and up through Y.

b) baffles me though.

Title: Re: Electronics Question
Post by: enpassant on April 12, 2011, 02:45:05 pm

b) V(XY) = 8 v, I = 8/7k = 1.1 mA, P, P.

Title: Re: Electronics Question
Post by: SDPHD on April 12, 2011, 06:00:36 pm

Thanks for the replies guys.

I asked my dad how to this.

First off, current flows from high potential to low potential. Which is something I didn't know.

For part a, for the 5kΩ resistor, V=5-0(At the ground point V=0, something else I didn't know). So V=5V, R=5000Ω. Therefore, I=V/R=5/5000=0.001A. Since point X is at 5V (higher potential) and ground is at 0V (lower potential), the current is flowing from X to ground, therefore, current is moving in direction P.

For part a, for the 2kΩ resistor, V=0--3. So V=3V, R=2000kΩ. Therefore I=V/R=3/2000=0.0015A. Since ground is at 0V (higher potential) and point Y is at -3V (lower potential), the current is flowing from ground to Y, therefore, current is moving in direction P.

For part b, I applied the same theory (without ground of course) but I got an answer different to that in the worked solutions. I think the solutions may be wrong, then again, there's a higher probability I'm wrong.

Title: Re: Electronics Question
Post by: SDPHD on April 13, 2011, 11:14:35 am

I'm back with another question. :-[

(http://i.imgur.com/pnnk7.png)

For part a, I thought that 20, 25, 10 and 5 are in series but according to the answers, its 5, 10 and 25 only. Why is this?

And for part b, I thought 15 and 10 were in parallel but according to the answers 5, 10 and 25 are in parallel with 15. Why is this?

Does it have anything to do with the ground point or is my thinking just totally wrong?

Thanks.

Title: Re: Electronics Questions!
Post by: evaever on April 13, 2011, 08:31:22 pm

where have all the helpers gone

Title: Re: Electronics Questions!
Post by: xZero on April 13, 2011, 08:39:48 pm

nobody likes electronics rofl (me included), ill try and explain it

a) the current went from the battery(150v) up and to the right where it hits the first split, it will split up into 2 currents, 1 goes through 15 ohms and the other goes through 5 ohms. Lets focus on the 5ohm current, it continues to the right until the next split, however the line with 30 ohms is not connected to anything, hence it will go through the 10 ohms only. It continues onward until it passes the 25 ohms and meet up with the other current. So 1 of the current went through the 15 ohms but the other 1 went through 5, 10 and 25 ohms so they are in series.

b) the 2 currents are parallel to each other, which means that the 15 ohms is parallel with 5,10 and 25 ohms

hope I helped

Title: Re: Electronics Questions!
Post by: cranberry on April 27, 2011, 02:34:34 pm

i want to kiss u after that response