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# AQA Physics PHYA1 - 24 May 2016 - RESIT [Exam Discussion Thread] Watch

1. can someone please explain Vrms and I rms.

i know how to work it out but i dont know what it is ?
2. (Original post by Exams987)
can someone please explain Vrms and I rms.

i know how to work it out but i dont know what it is ?
It's defined as the DC voltage or current that produces the same heating effect or power as it's AC equivalent
3. (Original post by Exams987)
can someone please explain Vrms and I rms.

i know how to work it out but i dont know what it is ?
Root mean square value (rms) is the value of the current or voltage that gives the same heating affect ( power output) for a d.c circuit that an a.c does through the same resistor.

So for I rms

P =I^2 R .....direct current ... but for a.c we choose half the peak value ... as it is not at the maximum all of the time. ... for A.c P = 0.5 x I^2 x R

Making these two equal

I^ 2 rms x R = 0.5 x I^2 x R .... we can cancel the R's

I^2 rms = 0.5 x I^2

Hence I rms = square root of I^2 / 2

Hence we get

I rms = I (peak) / root 2.

Hope that helps
4. (Original post by Billsonbubbles)
Root mean square value (rms) is the value of the current or voltage that gives the same heating affect ( power output) for a d.c circuit that an a.c does through the same resistor.

So for I rms

P =I^2 R .....direct current ... but for a.c we choose half the peak value ... as it is not at the maximum all of the time. ... for A.c P = 0.5 x I^2 x R

Making these two equal

I^ 2 rms x R = 0.5 x I^2 x R .... we can cancel the R's

I^2 rms = 0.5 x I^2

Hence I rms = square root of I^2 / 2

Hence we get

I rms = I (peak) / root 2.

Hope that helps

thanks do we need to know the proof?
5. (Original post by Exams987)
thanks do we need to know the proof?
no
6. (Original post by Exams987)
thanks do we need to know the proof?
nope
7. (Original post by Exams987)
thanks do we need to know the proof?

No , but at this rate ( how my AS resits are going) I would not be surprised.
8. (Original post by Billsonbubbles)
No , but at this rate ( how my AS resits are going) I would not be surprised.
what resit did you take?
9. (Original post by Billsonbubbles)
No , but at this rate ( how my AS resits are going) I would not be surprised.
is it possible if you upload the paper you have made ?
10. (Original post by TajwarC)
I think the 6 mark question will be either on finding an I-V characteristic or something to do with oscilloscopes. Maybe something on the photoelectric effect or line emission spectra. Unlikely to be on particles as this came up last year
What can they ask about line emission spectra and oscilloscopes that will be 6 marks?
11. Has anyone else seen the new spec for AS?
12. (Original post by Improvement)
What can they ask about line emission spectra and oscilloscopes that will be 6 marks?
June 12 had a 6 mark question regarding verifying the accuracy of a power source's rms using an oscilloscope. I've only seen a couple questions (excluding calculations) that involve oscilloscopes.

June 11's 6 marker was on how line spectra support the theory of atoms having discrete energy levels.
13. Wishing you all the best for tomorrow, hope it all goes well for you guys
14. can someone please explain potential dividers
15. (Original post by Exams987)
is it possible if you upload the paper you have made ?
Sure 1 sec I just need to find it on my computer ...i'll upload it on this thread as a word doc
16. (Original post by Billsonbubbles)
Sure 1 sec I just need to find it on my computer ...i'll upload it on this thread as a word doc
thanks
17. (Original post by Exams987)
can someone please explain potential dividers
Potential dividers are retty much where you have two or more resistors in series ( If you read back quite a few pages in this thread you will see that I have explained the types of circuits associated with them.

But in all honesty you just need to be familiar with your VI graphs and the components such as LDR'S and themristors and the relationship they have with resistance and light or temperature respectively.
18. (Original post by TajwarC)
June 12 had a 6 mark question regarding verifying the accuracy of a power source's rms using an oscilloscope. I've only seen a couple questions (excluding calculations) that involve oscilloscopes.

June 11's 6 marker was on how line spectra support the theory of atoms having discrete energy levels.
horrendous 6 markers, also fellow Bengali!!
19. (Original post by TajwarC)
June 12 had a 6 mark question regarding verifying the accuracy of a power source's rms using an oscilloscope. I've only seen a couple questions (excluding calculations) that involve oscilloscopes.

June 11's 6 marker was on how line spectra support the theory of atoms having discrete energy levels.
Can you link the mark schemes to these questions please so I can have a look please
20. (Original post by Improvement)
Can you link the mark schemes to these questions please so I can have a look please
http://www.aqa.org.uk/subjects/scien...d-mark-schemes

All here

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