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# OCR A2 Physics A: G484 & G485 - 15 & 21 Jun 2017 [Exam Discussion] watch

think i got 0.05 arc seconds or something possibly?
Same, Thought it was alright. The magnetic resonance question was weirdly worded.
2. the units pissed me off, used 10^-9 as micro rather than 10^-6, got nano correct though
3. (Original post by disposable2123)
Same, Thought it was alright. The magnetic resonance question was weirdly worded.
they asked about the concept of magnetic resonance rather than the device, I just stated the larmor frequency, relaxation time, precession about the magnetic field and radio wave stuff.
4. what did you guys do for the experimental calculation for the time constant. I said to put a voltmeter parallel to the capacitor and measure voltage after a period of time, then to use v=v(initial)*e^-(-t/CR) to work out CR.
what did you guys do for the experimental calculation for the time constant. I said to put a voltmeter parallel to the capacitor and measure voltage after a period of time, then to use v=v(initial)*e^-(-t/CR) to work out CR.
i said put a voltmeter in parallel to the capacitor and get a stop watch, discharge the capacitor noting the initial voltage, wait for the voltage to become 1/e of the initial and the time on the stopwatch is then the time constant
6. (Original post by Super199)
Difficult paper or what?
I found it really hard, there were some really strange questions
i said put a voltmeter in parallel to the capacitor and get a stop watch, discharge the capacitor noting the initial voltage, wait for the voltage to become 1/e of the initial and the time on the stopwatch is then the time constant
Both methods work I guess, remember any other difficult/interesting questions?
8. What did you guys put for the direction of the magnetic field on the first question? and also the final part to the capacitor question which was the time taken to get to a voltage of 1 v?
What did you guys put for the direction of the magnetic field on the first question? and also the final part to the capacitor question which was the time taken to get to a voltage of 1 v?
first question was motion in terms of the forces depending on the type of field, if magnetic, as the field and the electron and in the same direction of motion, there is no resultant force, therefore electron continues with constant velocity.

last capacitor question was just substituting values in v=v(initial)*e(-t/CR), but i used the wrong unit for the capacitor :/
i said put a voltmeter in parallel to the capacitor and get a stop watch, discharge the capacitor noting the initial voltage, wait for the voltage to become 1/e of the initial and the time on the stopwatch is then the time constant
Same
first question was motion in terms of the forces depending on the type of field, if magnetic, as the field and the electron and in the same direction of motion, there is no resultant force, therefore electron continues with constant velocity.

last capacitor question was just substituting values in v=v(initial)*e(-t/CR), but i used the wrong unit for the capacitor :/
for the first question i meant the part which was 1 mark which said state the direction of the magnetic field? and what was the inital voltage?
12. What did anyone get for the density of bone?
for the first question i meant the part which was 1 mark which said state the direction of the magnetic field? and what was the inital voltage?
oh, I wrote out of paper using left hand rule since it was a positively charged particle. Don't remember the initial V
What did anyone get for the density of bone?
couldnt understand how to do it
What did anyone get for the density of bone?
It was density of the muscle wasn't it? followed by working out the Z for the bone.
for the density I just used Z/1600 = density as Z=pc
It was density of the muscle wasn't it? followed by working out the Z for the bone.
for the density I just used Z/1600 = density as Z=pc
oh yeah density of muscle, i did that too, but it did ask something about bone in the last part which i didnt understand
What did you guys put for the direction of the magnetic field on the first question? and also the final part to the capacitor question which was the time taken to get to a voltage of 1 v?
Using FLHR (used FBI mnemonic [force, magnetic flux density, current]), F was towards centre of circle, and I was clockwise, so B out of the paper, towards you.

The final part had an initial voltage of 1.5, final of 1. t=2.43s (not sure if I remembered the capacitance correctly, used 1200microfarad)
Using FLHR (used FBI mnemonic [force, magnetic flux density, current]), F was towards centre of circle, and I was clockwise, so B out of the paper, towards you.

The final part had an initial voltage of 1.5, final of 1. t=2.43s (not sure if I remembered the capacitance correctly, used 1200microfarad)
remember any more questions?
the units pissed me off, used 10^-9 as micro rather than 10^-6, got nano correct though
think ive done the same
remember any more questions?
Acoustic impedance of bone was=7.55x10^6 so density=4720kgm-3.
I'll think of some more

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