The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread]

Scroll to see replies

Original post by a.a.k

What do I win? I'm just saying why 12*30 gave the wrong answer.
Reply 2781
Avatar for a.a.k
a.a.k
2
Original post by Paul Dirac
What do I win? I'm just saying why 12*30 gave the wrong answer.


Yeah i get it now

Posted from TSR Mobile
Original post by CD223
Without sounding really basic, what do we need to know about motors and stuff like DC motors in particular? I just wanna make sure my understanding is on a par with the expectation haha.


Posted from TSR Mobile

It's not on the spec:http://filestore.aqa.org.uk/subjects/specifications/alevel/AQA-2450-W-SP-14.PDF
Have there been questions about stuff like dc motors in the past? I don't remember any from past papers, they usually only ask about rotating coil, flux linkage=BANcoswt and emf=BANwsinwt (and not to mention transformers/power stations)
(edited 8 years ago)
Question: Which radioactive sources (alpha, beta or gamma) are most suitable for:
i) To trace the path of an underground stream
ii) To kill cells ina tumour deep inside a human body
iii) To act as a smoke detector

I know iii would be alpha particles but what about the rest? Btw can someone explain why alpha radiation is good for use in smoke alarms? The cgp book is vague on this point ("Because it allows a current to flow but won't travel very far" :s )

EDIT: Whoops, wrong thread.
(edited 8 years ago)
Reply 2784
Avatar for a.a.k
a.a.k
2
Original post by Paul Dirac
Question: Which radioactive sources (alpha, beta or gamma) are most suitable for:
i) To trace the path of an underground stream
ii) To kill cells ina tumour deep inside a human body
iii) To act as a smoke detector

I know iii would be alpha particles but what about the rest? Btw can someone explain why alpha radiation is good for use in smoke alarms? The cgp book is vague on this point ("Because it allows a current to flow but won't travel very far" :s )


For part iii aplha particle are highly ionisimg which mean the kknock electron so atoms are now charged so charge floews

Posted from TSR Mobile
Original post by a.a.k
For part iii aplha particle are highly ionisimg which mean the kknock electron so atoms are now charged so charge floews

Posted from TSR Mobile

Ah that makes more sense, thanks. But why would it be useful for a smoke alarm?

(Btw sorry this should be in the PHYA5 thread, I just forgot to post it there)
Reply 2786
Avatar for a.a.k
a.a.k
2
Original post by Paul Dirac
Ah that makes more sense, thanks. But why would it be useful for a smoke alarm?


When smoke particles block alpha particles there is no current so smaoke alarms sets off.

I am not 100% SURE

Posted from TSR Mobile
Original post by a.a.k
When smoke particles block alpha particles there is no current so smaoke alarms sets off.

I am not 100% SURE

Posted from TSR Mobile

But aren't the alpha particles the ones causing the alarm? So if they're blocked they can't ionize anything so a charge wouldn't flow (hence no alarm). Yeah it's slightly confusing but I hope they don't ask anything as detailed as that. :redface:
Do we need to know C ∝ A/d for capacitance? (A=area of plates, d=plate separation)
Reply 2789
Avatar for a.a.k
a.a.k
2
Original post by Paul Dirac
But aren't the alpha particles the ones causing the alarm? So if they're blocked they can't ionize anything so a charge wouldn't flow (hence no alarm). Yeah it's slightly confusing but I hope they don't ask anything as detailed as that. :redface:


You r rihht except that alpha particles dont set alarm off. They are always arrivibg at detector. When smoke partice block alpha particles the detector doesnt detetect any alpha particles so alarms sets off. The detector detects aplha particles by detecting current.
Hopefully this makes sense. Someone on google might be able explain clearly as i am bot good with words

Posted from TSR Mobile
Sorry for the double post, but have there been questions that use C=C_1+C_2 and 1/C=1/C_1+1/C_2 for capacitors in parallel and series (respectively)?
Reply 2791
Avatar for a.a.k
a.a.k
2
Original post by Paul Dirac
Sorry for the double post, but have there been questions that use C=C_1+C_2 and 1/C=1/C_1+1/C_2 for capacitors in parallel and series (respectively)?


I havent seen any

Posted from TSR Mobile
can some one outline the steps of how a mass spectrometer and a cyclotron operate
thanks
Original post by a.a.k
You r rihht except that alpha particles dont set alarm off. They are always arrivibg at detector. When smoke partice block alpha particles the detector doesnt detetect any alpha particles so alarms sets off. The detector detects aplha particles by detecting current.
Hopefully this makes sense. Someone on google might be able explain clearly as i am bot good with words

Posted from TSR Mobile

Thanks, this made it a lot clearer.

I foud this which looks helpful: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/radiation/radioisotopesrev3.shtml
Original post by Paul Dirac
Sorry for the double post, but have there been questions that use C=C_1+C_2 and 1/C=1/C_1+1/C_2 for capacitors in parallel and series (respectively)?


No, that's required for OCR specification


Posted from TSR Mobile
Reply 2795
Avatar for a.a.k
a.a.k
2
Original post by Paul Dirac
Thanks, this made it a lot clearer.

I foud this which looks helpful: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/radiation/radioisotopesrev3.shtml


Cool

Posted from TSR Mobile
ImageUploadedByStudent Room1433630027.879071.jpg

I keep getting B, any help ? :smile:


Posted from TSR Mobile
Original post by Ilovemaths96
can some one outline the steps of how a mass spectrometer and a cyclotron operate
thanks

I can outline cyclotron, bit rusty with mass spectrometer (do we need to know about it? :frown: )

From the top a cyclotron is basically two D-shaped metal "dees" with a small gap between them. When a charged particle enters the cyclotron an alternating voltage across the plates which accelerates the particle across the gap between the dees. You need an alternating voltage because the particle crosses the dees in one direction and after it travels 180 degrees across the circle it crosses the gap again in the other direction. As the particle keeps accelerating across the dees its speed increases, and as r=mv/BQ, this means the radius of its circular path increases with time. If you work it out you'll find that the time the particle spends in each semicircular dee is constant, so the alternating voltage switches regularly no matter what the current radius of the particle.Eventually when the radius is large enough the particle leaves through a tunnel to a detector.
Original post by Mehrdad jafari
No, that's required for OCR specification


Posted from TSR Mobile

Thanks
For a rotating coil in a magnetic field:

When the coil is vertical the flux linkage is greatest and when the coil is horizontal the induced emf is greatest

I thought induced emf is the change of flux linkage so why when the coil is at right angle to the magnetic field lines the induced emf us zero? This sounds so unreasonable


Posted from TSR Mobile

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you