Physics Unit 1 HELP!

Hi I need help with question 6Bi on this paper:

http://filestore.aqa.org.uk/subjects/AQA-PHYA1-QP-JAN12.PDF

the MS says the answer is 12v but i just dont know how

someone explain PLZ

Reply 1

piguy

Original post by Momoals

Hi I need help with question 6Bi on this paper:

http://filestore.aqa.org.uk/subjects/AQA-PHYA1-QP-JAN12.PDF

the MS says the answer is 12v but i just dont know how

someone explain PLZ

Total Voltage in series = Sum of the Voltage drops at each component in series.
Total voltage in parallel is always the same...

So there is the same voltage drop at X as at R2 & Y as they're in parallel, which is just what X uses as you definitely know that... Then apply the rules to R1 to get the answer...

(edited 10 years ago)

Reply 2

Momoals

Original post by Piguy

still not too sure, if R1=12, X=12 then where did the 4.5 come from , arghh its hard to explain in text

for 1 mark it seems like it should be easy, but i dont understand it, can anyone give me a webpage that explains

(edited 10 years ago)

Reply 3

yodawg321

Post if you get it please

Reply 4

piguy

4.5? Where did you get that from? You only need that for part (a), not b(i)

It is simple, you're just over thinking it... voltage drop on the components on the right side (X, Y & R_2) is just X, because voltages in parallel are equal. You're told what X is.

So voltage in R1 = Total voltage - Voltage in X!

(edited 10 years ago)

Reply 5

yodawg321

Original post by Piguy

I think he got confused of the 4,5 V

Reply 6

piguy

Original post by yodawg321

I think he got confused of the 4,5 V

Makes the most sense, that's the trouble you get into if you use the mark scheme too much when doing past papers that you forget what the question is actually about :cool:

Reply 7

Momoals

Original post by Piguy

is this kirchoffs law?

so wait a min, the total voltage in a circuit: volatge in each component?

thanks for help guys but i guess ill need to ask my teacher about it

Reply 8

yodawg321

Original post by Momoals

is this kirchoffs law?

so wait a min, the total voltage in a circuit: volatge in each component?

thanks for help guys but i guess ill need to ask my teacher about it

Yeah it's Kirchoffs 2nd Law. In a closed loop sum of PD = EMF in a circuit. You're definition might be a but different as you're AQA

Reply 9

piguy

Original post by Momoals

is this kirchoffs law?

so wait a min, the total voltage in a circuit: volatge in each component?

thanks for help guys but i guess ill need to ask my teacher about it

You don't need to bother with Kirchoffs laws, they just complicate things (although you could very well answer the question using them i.e. 2nd law: sum pd = sum of emfs), it's a basic GCSE circuits concept:

Total Voltage in Series: you add Voltage of each component
Total Voltage in Parallel: it's always the same at each component

You can derive it from V=IR and the fact that the Total Current in Series is always the same; and total current in parallel is added...

(edited 10 years ago)

Reply 10

yodawg321

Original post by Piguy

Right, so R1 will use 12V
The circuit which includes R2 will use 12V too as we can treat them both as Series.
But in that circuit is X and Y and the resistor, do they ALL use 12v or are they split equally?

Overthinking this and I'm not even doing AQA physics! :s-smilie: