June 2011 G485-Fields, Particles and Frontiers of Physics

What does it mean by "describe the principles of ultrasound scanning"?? its on the specification sheet (OCR Physics A) under ultrasound (d). Please reply as soon as possible :smile:

Thanks

These are the bullet points I'm remembering for that:

- frequency of 20000Hz
- non-ionising
- distinguishes muscle and blood
- high intensities can be destructive

Reply 201

Roar.

c4 on monday followed by this on tuesday. FML.

Reply 202

jam.wa

8

Original post by Roar.

c4 on monday followed by this on tuesday. FML.

I feel for you.

Reply 203

Lolly1

Original post by Roar.

c4 on monday followed by this on tuesday. FML.

me too

plus fp1 on wednesday and chem unit 5 on friday
AWFUL WEEK

Reply 204

-Jaz-

Original post by jam.wa

There is SO MUCH PHYSICS!
Dream question:

'Fail to calculate this really difficult capacitor question'

I HATE capacitors more than anything.

Ahhh I could get full marks and then some in that! :P

Reply 205

ChoYunEL

1

Original post by Roar.

c4 on monday followed by this on tuesday. FML.

Further Pure 2 on Monday followed by this...
Then Mechanics 2 and Statistics 2 on Wednesday.

OCR has definitely screwed me over.

Reply 206

CoffeeStinks

11

Original post by jam.wa

Yeah, I've done every paper I can get my hands on. Don't you find you can't do some? On some of the Health/Cosmology ones, I'm getting max 2 out of 7 questions that I can do with my knowledge of the current syllabus.

Yeah I thought it was just me. It's a complete change in specification.

Reply 207

Acta Non Verba

7

Original post by jam.wa

These are the bullet points I'm remembering for that:

- frequency of 20000Hz
- non-ionising
- distinguishes muscle and blood
- high intensities can be destructive

+1

The only thing I'd add to that is that Ultrasound is a longitudinal wave rather than a transverse wave.

Reply 208

jam.wa

8

Original post by Acta Non Verba

+1

The only thing I'd add to that is that Ultrasound is a longitudinal wave rather than a transverse wave.

It's quite easy to forget that one. AS seems so long ago.

Reply 209

Acta Non Verba

7

Original post by jam.wa

It's quite easy to forget that one. AS seems so long ago.

True dat. Your points are better, but sometimes you can get marks for really basic stuff so it's worth having in there.

On a completely unrelated note:

I was having LOADS of trouble with Lenz's law, someone explained it to me like this and it helped a lot:

During electromagnetic induction you're inducing a current. Using the right hand rule you can find out the direction of said current. Make note of the direction of your thumb, which shows force.
However, we know that the flow of current also produces a magnetic field. If you now use your left hand you'll find that the magnetic field produced by this induced current provides a force in the opposite direction to the original magnetic field we associated with the electromagnetic induction. Thus, the current 'moves in such a way as to oppose the flux change that caused it.'

Reply 210

jam.wa

8

Original post by Acta Non Verba

True dat. Your points are better, but sometimes you can get marks for really basic stuff so it's worth having in there.

On a completely unrelated note:

I was having LOADS of trouble with Lenz's law, someone explained it to me like this and it helped a lot:

During electromagnetic induction you're inducing a current. Using the right hand rule you can find out the direction of said current. Make note of the direction of your thumb, which shows force.
However, we know that the flow of current also produces a magnetic field. If you now use your left hand you'll find that the magnetic field produced by this induced current provides a force in the opposite direction to the original magnetic field we associated with the electromagnetic induction. Thus, the current 'moves in such a way as to oppose the flux change that caused it.'

NO, this is an unrelated note:

Yes.
I bet Faraday was fuming when Lenz came along and bagged himself a law.
All Lenz did was put a minus sign infront of FARADAY'S equation!
And now the equation belongs to both of them.
Bloody Lenz!!!!

Reply 211

FristyKino

2

Electromanetic induction is probably the worst thing that has happened to me :frown:

Reply 212

M_I

Can someone explain this question, its from the cgp book page 65, question 2b

The time base on a CRO was set to be 50x10-6 s cm-1. Reflected pulses from either side of a fetal head are 2.4cm apart on the screen. Calculate the diameter of the head if the ultrasound travels at 1.5 kms-1.

Thanks...its 4 marks btw.

Reply 213

Roar.

How many marks is the paper out of? Is it 150?

Reply 214

Oh my Ms. Coffey

Original post by M_I

Can someone explain this question, its from the cgp book page 65, question 2b

The time base on a CRO was set to be 50x10-6 s cm-1. Reflected pulses from either side of a fetal head are 2.4cm apart on the screen. Calculate the diameter of the head if the ultrasound travels at 1.5 kms-1.

Thanks...its 4 marks btw.

I couldnt do that one, I find them hard to do unless its a show that.

Original post by Roar.

How many marks is the paper out of? Is it 150?

100.

Reply 215

magdaplaysbass

Original post by Roar.

How many marks is the paper out of? Is it 150?

the actual paper is out of 100, but the results are converted into ums; which are out of 150 :smile:

Reply 216

jam.wa

8

Original post by M_I

Can someone explain this question, its from the cgp book page 65, question 2b

The time base on a CRO was set to be 50x10-6 s cm-1. Reflected pulses from either side of a fetal head are 2.4cm apart on the screen. Calculate the diameter of the head if the ultrasound travels at 1.5 kms-1.

Thanks...its 4 marks btw.

time base - 50x10-6 s cm-1, pulse width - 2.4cm, ultrasound speed - 1.5 kms-1

- Work out the time difference between receiving pulse from the front of the head, and the back of the head first:

2.4 x 50x10-6 s cm-1 = 1.2 x 10-4 s

- Work out the difference in distance the echo has had to travel:

distance = speed x time; 1.5 x 10^3 x 1.2 x 10-4 = 0.18m

- Because this is the distance covered by the echo going to the back and then coming to the front again it's half this distance:

0.18/2 = 0.09m

Reply 217

Daave92

Out of interest, does anyone know the grade boundaries for the June 2010 paper and the Feb 2011 paper?