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

OP

Original post by Corectspelling

any explanation for question 19
http://filestore.aqa.org.uk/subjects/AQA-PHYA4-1-W-QP-JUN10.PDF

F = BIL

If the current is reversed in its direction, due to Fleming's LHR, the force will also reverse direction.

If the current is doubled in its magnitude, due to F = BIL, the force will also double in its magnitude.

The scale reads a force exerted on it by the magnet and wire combination. If F doubles and reverses its direction, then because the wire is fixed, an initial reading of 112g will now read -224g (= -2 x 112g).

Does that help?

Posted from TSR Mobile

Reply 1922

Corectspelling

1

Original post by CD223

F = BIL

If the current is reversed in its direction, due to Fleming's LHR, the force will also reverse direction.

If the current is doubled in its magnitude, due to F = BIL, the force will also double in its magnitude.

The scale reads a force exerted on it by the magnet and wire combination. If F doubles and reverses its direction, then because the wire is fixed, an initial reading of 112g will now read -224g (= -2 x 112g).

Does that help?

Posted from TSR Mobile

Why is it negative?

Reply 1923

gcsestuff

Do we need to know about the right hand rule? or is it just the left hand one :smile:

Reply 1924

PotterPhysics

6

Original post by gcsestuff

Do we need to know about the right hand rule? or is it just the left hand one :smile:

You only need left hand rule and Lenz's law.

Reply 1925

Absent Agent

21

Original post by Corectspelling

Why is it negative?

Because the scale was zeroed after the magnet was placed on the scale. So when you take the magnet of the scale then the scale will read negative of the mass of the magnet

Posted from TSR Mobile

Reply 1926

OP

Original post by Corectspelling

Why is it negative?

The scale was zeroed before any of the changes took place. If I'm honest it is a very badly worded question. If anyone else can shed light on this then I'd appreciate it.

Posted from TSR Mobile

Reply 1927

Absent Agent

21

Original post by CD223

The scale was zeroed before any of the changes took place. If I'm honest it is a very badly worded question. If anyone else can shed light on this then I'd appreciate it.

Posted from TSR Mobile

That's true. In fact most of the questions they ask are badly worded and lack details

Posted from TSR Mobile

Reply 1928

Corectspelling

1

Original post by Mehrdad jafari

Because the scale was zeroed after the magnet was placed on the scale. So when you take the magnet of the scale then the scale will read negative of the mass of the magnet

Posted from TSR Mobile

ahhhh i see, thanks m8 quite a tricky question :smile:

Reply 1929

Absent Agent

21

Original post by Corectspelling

ahhhh i see, thanks m8 quite a tricky question :smile:

No problem!
Yeah, they are quite tricky. In the exam don't judge a question too quickly. Read the question carefully before you answer it.

Posted from TSR Mobile

Reply 1930

OP

Original post by Mehrdad jafari

No problem!
Yeah, they are quite tricky. In the exam don't judge a question too quickly. Read the question carefully before you answer it.

Posted from TSR Mobile

I'd have got it wrong in the exam. I initially thought -112g as the actual change in weight is -224g, and I saw it was initially 112g, so I did 112 - 224.

Posted from TSR Mobile

Can anyone help?

Original post by CD223

I'd have got it wrong in the exam. I initially thought -112g as the actual change in weight is -224g, and I saw it was initially 112g, so I did 112 - 224.

Posted from TSR Mobile

The same here, when i first thought about the question. I didn't realise when the current is off the scale reads zero

Posted from TSR Mobile

Reply 1933

OP

Original post by huniibehi

Can anyone help?

ImageUploadedByStudent Room1432649012.995558.jpg

Reply 1934

Leonacatherine

Just done january 2012, im going through the papers in chronological order starting from 2010, I found this one a lot more difficult than the previous ones is anyone else the same? I still managed to get two marks of an A* but that was with about half an hours extra time hahaha! Anyone able to explain a couple of question, im still not sure on a few after seeing the mark scheme

Reply 1935

OP

Original post by Leonacatherine

Just done january 2012, im going through the papers in chronological order starting from 2010, I found this one a lot more difficult than the previous ones is anyone else the same? I still managed to get two marks of an A* but that was with about half an hours extra time hahaha! Anyone able to explain a couple of question, im still not sure on a few after seeing the mark scheme

The papers have been getting progressively harder. June 2014 MC was the hardest I've seen.

Which questions are you referring to? :smile:

Reply 1936

Leonacatherine

Original post by CD223

The papers have been getting progressively harder. June 2014 MC was the hardest I've seen.

Which questions are you referring to? :smile:

great -____- That sucks! I'd been feeling pretty confident before this paper :frown:

There are a few im not sure on first was the multiple choice 15 I knew it had to be either c or d, normally i use ratios but because this was a force question its proportional to r^2 so i wasnt sure how to work it out

Reply 1937

Leonacatherine

Also for question 3bii I dont get why you couldnt use the formula Vmax = 3 pi FA to work out the amplitude mark scheme required v =2pi f x square root A^2-x^2
http://filestore.aqa.org.uk/subjects/AQA-PHYA4-2-W-QP-JAN12.PDF
sorry was taking too long to upload images

OP

Original post by Leonacatherine

great -____- That sucks! I'd been feeling pretty confident before this paper :frown:

There are a few im not sure on first was the multiple choice 15 I knew it had to be either c or d, normally i use ratios but because this was a force question its proportional to r^2 so i wasnt sure how to work it out

Question 15
ImageUploadedByStudent Room1432651735.940124.jpg

Reply 1939

OP