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

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Reply 3080

noseypo

Whats the difference between a dynamo and a generator??

Reply 3081

noseypo

Original post by NEWT0N

They're the same (I think): The main function of both is to convert kinetic energy to electrical energy.

Are they both to do with generating emf?

Reply 3082

Leonacatherine

Anyone able to explain why the periodic frequency being in phase with velocity makes it resonate? Why can't it be in phase with displacement

Please don't just reply with natural frequency equalling applied frequency haha

Can anyone give the aqa definition of resonance ?

Reply 3083

thedon96

can someone please definitively explain the different degrees of damping? My teacher and textbooks all say different things about heavy, critical and overdamping :frown:

Reply 3084

Leonacatherine

Original post by thedon96

can someone please definitively explain the different degrees of damping? My teacher and textbooks all say different things about heavy, critical and overdamping :frown:

I haven't heard about over damping on this spec but critical damping is when it stops the system oscillating after being released from equilibrium and heavy damping is when there is no oscillation at all, it never reaches equilibrium. On a graph it would be a straight line that slopes downwards gradually but doesn't pass the midpoint
:smile:

Reply 3085

Specter

Hey who here does Section B first? Was wondering whether doing the long questions first would be better because i invest too much time into the multiple choice.

Reply 3086

Leonacatherine

Original post by NEWT0N

Not sure if this is what you're looking for but here's a try.

If you think about pushing someone on the swing you want to time your push so that you push them as soon as they momentarily stop when they reach your hand. At that point their velocity is on the verge of switching direction from "towards your hand" to "away from your hand", so when you push right when their velocity changes to "away from your hand" you are pushing in phase with the velocity. (If you plot the graph of displacement vs time for your hand and the swing they'll be the same with possibly different amplitude because your hand has the same period as the swing and is also always at the same direction as the swing so there is no "lag" between you and the swing and the two are consequently in phase.)

Hey thanks! I get the swing metaphor but the brackets bit at the end confused me haha

I think I might be overthinking it haha but if you could wouldn't you push them at the top of their swing to make the amplitude even greater?

Reply 3087

Adangu

Original post by Specter

Hey who here does Section B first? Was wondering whether doing the long questions first would be better because i invest too much time into the multiple choice.

I'd aim for either 60 long/45 Mc

or 55long/50 Mc

Definitely spend longer on long questions. If worse comes to worse you can always guess the Multiple choice if you run out of time. Not recommended tho just saying :smile:

Reply 3088

Adangu

Original post by Specter

Hey who here does Section B first? Was wondering whether doing the long questions first would be better because i invest too much time into the multiple choice.

I'd aim for 60long/45Mc

or 55long/50Mc

Definitely spend longer on written section. If worse comes to worse you can guess the multiple choice. Only if you run out of time that is :smile:

Reply 3089

Lau14

Original post by NEWT0N

This might be a silly question but why does the MC answer sheet have 50 response boxes

Because it's a general AQA one, not a PHYA4 specific one I think :smile:

Reply 3090

Specter

Original post by Adangu

I'd aim for 60long/45Mc

or 55long/50Mc

Definitely spend longer on written section. If worse comes to worse you can guess the multiple choice. Only if you run out of time that is :smile:

Yeah thats how I usually try to split my time. But as soon as I dont get the answer for a MC question I spend ages trying to work it out then realise I have less time for the long answer qs :frown:

Reply 3091

Kennethm

what did everyone here get first time for the aqa june 2014 MC part?

Reply 3092

Specter

Original post by Kennethm

what did everyone here get first time for the aqa june 2014 MC part?

I found that the hardest one, got 19/25 but some questions were a fluke. You?

Reply 3093

gcsestuff

Original post by Kennethm

what did everyone here get first time for the aqa june 2014 MC part?

14 in January lol

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Reply 3094

gcsestuff

But I redid I recently and got 20, I get between 18-21

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Reply 3095

CD223

Original post by Kennethm

what did everyone here get first time for the aqa june 2014 MC part?

When I did it back in December 2014 I got 18. Improved since then thankfully :tongue:

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Reply 3096

Kennethm

woah all these replies - I did it a long time ago and did it for the first time today basically going into it without remembering what it was before and I must say this is certainly the most difficult MC I've done. The others pale in comparison and I nearly ace the others...

Im sure its been posted here before but could someone explain Q13 from that paper please? Its here : http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN14.PDF

Cannot wrap my head around it.

Reply 3097

Kennethm

Original post by NEWT0N

June 2010 6 marker: "This ismost important for the high current winding (the secondary coil of astep-down transformer)."

Please explain what this means :smile:

theres more current in that winding and since energy lost is proportional to I^2 (current squared) it means more energy is lost because there is simply more current in it.