AQA Physics PHYA5B (Medical Physics) - 28th June 2016

It was awful. I also ran out of time so I didn't even make a start on the X-ray question so that's an instant 6 mark gone.

Really? I thought it was okay apart from the last question... which parts did you struggle with?

What rhe **** was that mrad-1 question?

Bits from everywhere. For example, the piezoelectric one, I forgot the word 'polarity' so I just left it blank and forgot to go back to it so now my answer reads like 'There is an electrode on either side of the piezoelectric crystal and when an alternating current is applied across it. At a BLANK, the crystal expands which pushes the air in front of it. The crystal contracts when the BLANK is reversed. This sequence is repeated millions of times per second and this creates a pressure wave which is the ultrasound wave.

Exactly, I don't even remember covering this in the damn specification.

The diameter I got came to 6 (or something else) x10^-6 metres

I had no clue at all. Not even a general equation i could think of, so I just did the mrad-1 value divided by 2pi (couldnt remember how to convert radians to angles) then did sin(ans)/ diameter. Defo wrong.

I don't think you need to talk about polarity

June 2013- Outline, with reference to the diagram, the process by which the transducer produces ashort pulse of ultrasound. (4marks)

Alternating potential difference applied across the crystal/causes crystal to expand and contract/creating pressure waves in the crystal / plastic membrane /frequency of alternating pd equal to that of crystal /resonant frequency ofcrystal which is above 20 kHz/short application of ac to produce short pulse /use of backing material to damp and stop vibration of crystal 
I mentioned points 1,2,4,5

Exactly, I don't even remember covering this in the damn specification.

The diameter I got came to 6 (or something else) x10^-6 metres

Did it want us to treat it like the visual acuity calculation? I also forgot the 'x2' which means I've got it wrong...

Is anyone going to make an unofficial mark scheme for the Medical Physics paper?

How many marks do you think I got for that?

Did it want us to treat it like the visual acuity calculation? I also forgot the 'x2' which means I've got it wrong...

56.7% or something for percentage one. Spatial resolution for first question.
Lens gets fatter when looking near, thinner when far. Ciliary muscles vhange it.
Pupil dilates for low light, gets smaller for bright light.

56.7% or something for percentage one. Spatial resolution for first question.
Lens gets fatter when looking near, thinner when far. Ciliary muscles vhange it.
Pupil dilates for low light, gets smaller for bright light.

I dont even know what that is

2 x (average separation of light-sensitive cells on retina) / distance from retina to optical centre of the eye.) = Visual Acuity (radians)