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

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Reply 80
can someone please explain Vrms and I rms.

i know how to work it out but i dont know what it is ?
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
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
Reply 83
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?
Original post by Exams987
thanks do we need to know the proof?


no
Original post by Exams987
thanks do we need to know the proof?


nope
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.
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?
Reply 88
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 ?
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?
Has anyone else seen the new spec for AS?
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.
Wishing you all the best for tomorrow, hope it all goes well for you guys :smile:
Reply 93
can someone please explain potential dividers
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
Reply 95
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
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.
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!!
(edited 7 years ago)
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 :smile:
Original post by Improvement
Can you link the mark schemes to these questions please so I can have a look please :smile:


http://www.aqa.org.uk/subjects/science/as-and-a-level/physics-a-2450/past-papers-and-mark-schemes

All here

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