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

I know! Test was particularly horrid so I'm not looking forward to my marks back on Tuesday.

Oh right! I need to somehow got a mountain of work all into tomorrow - this weekend is so unbelievably busy!


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You never know, it might have gone okay!

All I have this weekend is work Sunday morning and Sunday dinner at nan and grandads, so the usual! Plenty of time for sleep (and work) tomorrow

I don't think it did... :/ Some of the questions just felt like they were too hard to be exam questions? Aha.

Aw that sounds chilled! I had work tonight and then again on Sunday afternoon ugh - need to work on my motivation!


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That sucks then :/ maybe they aren't real questions...? (wishful thinking )

Fortunately I only have to work once a week in term time usually!

Yeah I hope they weren't! Oh lucky! I think if I did 3 subjects it would be more manageable but at the moment it's just non stop ahah


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Yh 3 (+ 1/2... we never finish on time) hours of work on a Saturday or Sunday morning when I pretty much wouldn't be awake (or not conscious enough to do anything) anyway doesn't really make much of a dent in my life tbh except that lovely bit where I get paid. I even get a lie in usually compared to college, it's just up the road so I don't get up until 9, but I'm working the earlier start this weekend ugh :/

Oh wow! I do 8 contracted hours a week but often work like 12 hours instead due to overtime. It's not bad as its only a 5 minute walk from my house so like yourself I just roll out of bed aha! That said it does make my life hectic!


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0 hour contract There are enough of us working there (you need eight people for a normal shift) to not have to do a double weekend very often (although when a shift needs covering, it's me that gets asked. We were very short staffed over the summer and had to train up new ones because people usually move on to waiting when they're 16 and some people left for other reasons all at around the same time, and while people are being trained they can only do one of the four jobs at the start - so only 2/8 people can be the new ones technically - and you also need additional people in on top of the 8 to do the training. We physically didn't have the numbers so I was working 5 or so days a week instead of the usual 3 that we get in the holidays... didn't have the relaxing summer I expected and barely did or saw anything. One poor girl worked 9 days straight.)

Ah sounds good yet also stressful in places! To be honest I don't think there's a lot of jobs out there for our age group without a flaw!


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I generally like my job, it's usually hard work but not in an entirely awful way. I couldn't do waiting or anything else really, too socially awkward/incapable of balancing a tray!

Ahahah me too!
Sorry, but do you know the reasons behind why a solid ring on a magnetised rod oscillates up and down when an ac current is applied to the coil connected to the rod?


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Ahahah me too!
Sorry, but do you know the reasons behind why a solid ring on a magnetised rod oscillates up and down when an ac current is applied to the coil connected to the rod?


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It'll be something to do with the... left hand rule maybe? magnetic field is always in the same direction, so as current direction flips back and forwards (AC) the force switches direction.

Are you aware Lenz' law?

Ah right! Thank you.


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I am - direction of induced emf and hence the induced current is always such as to oppose the change that causes it. To my understanding:

1. An ac current is applied to the coil, which generates a changing magnetic flux linkage around the coil and rod.

2. A solid ring is dropped over the rod, cutting its surrounding magnetic flux lines.

3. As there is a changing magnetic flux linkage per unit time as it is passing through the solid ring, there is an induced emf.

4. As the ring is solid, there is an induced current in the ring. This induced current has its own surrounding magnetic field.

5. The two fields (generated around the ring and around the coil/rod) oppose one another due to Lenz's law (the ring originally travels downwards so the field it has is upwards whilst the field is downwards for the coil/rod).

6. Due to this the ring travels upwards as the current switches direction many times so the field directions reverse, causing the ring to no longer be pushed up the rod, allowing it to fall again(?).

7. This process of switching field directions repeats itself many times until the ring's field equally opposes the coil/rod field.

8. The oscillations gradually reduce in amplitude until the ring reaches an equilibrium point where both fields "cancel" and the ring may be seen to vibrate in 'mid-air'.



Is my understanding correct? It's just I've no idea about the bit where fields oppose each other! I get that a field exists around both the ring and the rod but I'm unsure about why it oscillates!



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Yeah possibly more likely something to do with Lenz's law but still haven't gotten around to fixing my magnetic fields knowledge so

Me neither which is why I've no idea as to why it oscillates!


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Well, I'll get around to it soon (ish)! Would be done this afternoon definitely, just coming to the end of gravity, but I've got to go shopping :/

Shopping sounds more fun...haha! I've just finished Astro homework on lenses. Fun.


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Yeah not any fun sort of shopping :/ I needed new trousers for work but mum needed to get the weekly food shop as well.

Ick :/ fortunately we never really have homework for Physics (kind of makes up for the huge volumes of Chemistry hw). But now I have to finish those physics notes today (finally), do a unit 4 chemistry paper today and finish both of my maths hws before Monday.