Edexcel Unit 4: Physics on the Move 6PH04 (11th June 2015)

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Reply 80

Regina15

Original post by cerlohee

I don't know how to answer this but have you looked at the examiner's report?

Thanks for replying :smile:

I shall have a look at it

Reply 81

username1162972

If you guys don't know. There are 100s of Unit 4 questions on Scribd relevant for our current syllabus from pre 2009 papers.

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Reply 82

The Best1

Original post by cerlohee

Spoke to my teacher and it was just a misunderstanding of the phrase "when the switch is closed"
I thought it meant the act of physically closing the switch, which would generate an EMF. However, it only meant that the switch is not open.

I think when you close the switch, voltage starts travelling through the circuit but it is not enough to make the lamp light up? When you open the switch, the magnetic field created by the coil will suddenly go to zero, so a change of magnetic flux (BA) in a time period will produce an emf, which is enough to make the neon lamp flash in that second.. that would be my answer

Reply 83

The Best1

Original post by Regina15

Could someone please help with his question! I can't figure out how to use the equation V=V0e^-t/rc here, and the mark scheme is no help. Any help would be appreciated :smile:

It's question q16 c) ii) that I can't figure out, thanks :smile:

If you look at the graph, you have to use your own best estimates when working with this,

*These are all to my best estimates* If you look at 4ms, there was 5V. This goes down to 4V at 7ms. From the previous question which you did not include, you need to use the capacitance value given to you.

V=V0e^-t/RC

You have V as 4v, V0 as 5V,

t as 3ms (the difference between 7ms and 5ms)

and capacitance as 10 x 10^-6

Substituting in the values you should get ln0.8=e^-3/RC

go ahead and ln both sides to get RC = -3/ln0.8

then since you know the C (capacitance) value, just simply find the resistance. the value I got was around 1500 which is the range they asked for

Reply 84

The Best1

Original post by physicsmaths

If you guys don't know. There are 100s of Unit 4 questions on Scribd relevant for our current syllabus from pre 2009 papers.

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can you tell me more about this??

Reply 85

cerlohee

Original post by The Best1

The same EMF is generated when the switched is closed as to when it's opened, and a magnetic field is produced in both circumstances! I just misinterpreted the wording :smile:

Reply 86

The Best1

Original post by cerlohee

The same EMF is generated when the switched is closed as to when it's opened, and a magnetic field is produced in both circumstances! I just misinterpreted the wording :smile:

yeah, from what our teacher said, she assumed the wording on the question was right(?) and the reason why is because: when the switch is closed, there is a "switch mechanism" so it takes longer for the current to travel through the lamp/coil. bigger t means smaller EMF, so that's why the neon lamp does not light up. but when you open the switch, the current instantly dies out so a very small t value: very big emf, hence why the bulb lights up..

Reply 87

cerlohee

Original post by The Best1

I don't think that's true. A magnetic field is generated by current through a wire, the direction is irrelevant. I've never heard of the switch mechanism? Do you think that AC generators work in the same way?
I mean I don't agree. Your teacher's answer sounds like an explanation to solely fit the misunderstood version of the question. Can anyone here offer their opinion?

Reply 88

The Best1

i have never heard of the switch mechanism either, but when we had to do this experiment in class, the neon bulb did not flash when the circuit was connected but it flashed when the switch was opened

i didn't say anything about the induction of mg. field, but the explanation they gave us went something like, the "switch mechanism" means when the switch is closed, it just takes a bigger time value for BA to be cut. but when the switch is opened, it goes from whatever the BA value to 0 in a much smaller t value (instantly), which is why it has a bigger EMF value..

This explanation was from like 3-4 months ago, so I could be wrong with the way I explained it, but I definitely remember a "switch mechanism" to do with the time value being mentioned for this experiment/problem

Reply 89

username1162972

I just did this question. Input would be nice.
We note that before the switch is opened (instantly) there is a current hence a magnetic field in the coil. as the switch is opened the current drops hence there is a change in magnetic flux therefore change in flux linkage. Therefore inducing an emf allowing the lamp to flash. It flashes once as in the subsequent time (instants after the flash as it is very quick) there is no change in flux linkage since there is no change in flux linkage therefore no emf is induced.
I am not sure sure what paper this is so could someone say how many marks I would get. I feel as if I have missed something out and would get 3/4.

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Reply 90

Regina15

Original post by The Best1

Thank you so, so much! This is brill!
That helped a whole lot :biggrin:

Reply 91

haappy17

Hey guys! Do any of you have notes on the magnetic fields chapter? the whole magnetic flux and flux linkage and cutting flux lines is very confusing.

I find it really hard and the CGP doesnt have a lot of information! Thanks!

Reply 92

Regina15

Original post by haappy17

Try physicsandmathstutor.com or 'Dr Physics' on you tube, I found both quite helpful

Reply 93

minroi#01#

The chemistry unit 03 paper was **** hard for the first time in my life :P I mean the real june 2015 paper..

Reply 94

jay_em

So what techniques are people using to revise Physics? I'm averaging about 50/80 on practice papers, but I'm not sure what to do next to improve that.

Reply 95

Tredoltle

Original post by jay_em

So what techniques are people using to revise Physics? I'm averaging about 50/80 on practice papers, but I'm not sure what to do next to improve that.

Try some of the international a level papers.
Trying the normal past papers I average about 57, and when I did jan 13 i was above that. But when I did a unit 4 mock in school (jan 2015) I ended up with a miserable 30/80 (it was so hard with very high grade boundaries) so these international papers could prepare you for some hard questions.
I really hope edexcel goes easy this time after last year's horrible unit 1 paper.

Reply 96

The Best1

Original post by Tredoltle

i average around 57 too on unit 4, i think i've done all of the reserved papers unless there are more january 2013 and before? haven't tried IAL papers, but should give it a go too. i genuinely think unit 4 is harder than unit 5, anyone else feel the same way?

Reply 97

Wannabe007

Original post by The Best1

Got a 45/80 in my mock for unit 4 and 67/80 for unit 5. Unit 4 is definitely harder than unit 5. Just like unit 1 being harder than unit 2.

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Reply 98

Hectors

Original post by Wannabe007

Got a 45/80 in my mock for unit 4 and 67/80 for unit 5. Unit 4 is definitely harder than unit 5. Just like unit 1 being harder than unit 2.

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Very subjective, once you get the gist of unit 4 you realise that it is on par with unit 5. Though I agree with you that last years unit 1 paper was definitely harder than the unit 2 one.

Reply 99

Wannabe007

Original post by Hectors

Very subjective, once you get the gist of unit 4 you realise that it is on par with unit 5. Though I agree with you that last years unit 1 paper was definitely harder than the unit 2 one.

Hopefully I'll be able to master unit 4 within the two week break I have. How would you recommend to prepare for it? Im almost done with all the papers and plan to do them again.

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