AQA Physics PHYA4 - 20th June 2016 [Exam Discussion Thread]

how many marks was for RC and for resistance. if i did rc wrong because of ln 0.8 i got 1/3???? does that mean i get 1/2 for resistance for follow thru?

Wasn't it V = -mv/N?

Yeah -mv because it was a velocity so had to be going in the opposite direction to conserve momentum!

how many marks was for RC and for resistance. if i did rc wrong because of ln 0.8 i got 1/3???? does that mean i get 1/2 for resistance for follow thru?

It clearly said recoiling nucleus.

if its recoiling it mustve already emitted the alpha

Here are my answers to Written, the question parts might not be correct.

Written answers
1ai) 8.26 (will be a range)
ii) 2.6x10^-4

bi)28
ii)5.9x10^4
iii) bottom box ticked

2ai) Derivation
ii) 6.06x10^6 (3SF only)

b) Downward Curve staring at 9.81
Minimum at g=0 at a point slightly offset from halfway closer to Venus
Rises up to 8.87

3a) V=mv/N

b) Derivation

ci) 1.15x10^-19 kgms-1 OR Ns

cii) Anti electron neutrino released also so Beta minus particles have range of Kinetic Energies upon release.

4a) Small amplitude oscillation as only valid for small angular amplitudes.

b) -Set up light string with Bob on the end,
attach top of string to clamp stand boss.
-Measure length from top to centre of Bob.
-Release the Bob so it oscillates with small amplitude.
-Use stop clock to measure time taken for 20 oscillations.
-Divide this by 20 for mean T
-Plot T^2 against L
-Calc Gradient
g=(4pi^2)/gradient
-Repeat procedure

c) -Student value 4x true value
-Time period half so all values for T^2 will be 1/4 the true
-Gradient is 4x lower
-State equation or show that g is inversely proportional to gradient.

5a) Lenz's Law: Direction of induced EMF/current is always in a direction that opposes the change that caused it.
Faraday's Law: Induced EMF is proportional to rate of change of flux linkage.

b) -Change in flux linkage when current flows.
-EMF induced in wheel (or whatever it was called)
-Current induced in the wheel as good conductor.
-Current carrying conductor (wheel) opposes the field due to coil, therefore there is a force against the direction of motion.

c) Wheel not in contact with electromagnet so no wear, but in brake pads there is wear due to friction.

More energy used or less effective or heating.

i swear to conserve momentum
mv=NV
but the velocity of v was in opposite direction so
-mv=NV
V=-mv/N

i wrote the negative in brackets, so if the negative is wrong will i lose the marks?

216 was the nuclean number

That's not quite it. The momentum before was zero, and the momentum after was (N)(V)+(m)(-v) as the alpha particle is going in to opposite direction to the daughter nucleus (momentum is a vector so . . .).

As momentum is conserved, 0=NV-mv
Taking mv over you get NV=mv

Yeah thanks I was just remembering from the y axis (will edit in a second) - did it give the units or did we have to write them?

220


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Was the capacitance in the first question 8.2 microfarads????