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

Reply 2080

alex_david97

5

unofficial mark scheme for section B?

Reply 2081

lucabrasi98

15

Original post by DesignPredator

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) No external forces

bi) V=mv/N

bii) Derivation

ci) 216
ii) 1.15x10^-19 kgms-1 OR Ns
iii) 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.

Either your 5a is wrong or the AQA text book is wrong. Because the text book says induced emf is EQUAL to rate of change of flux linkage. Not proportional. Plus if it was proportional then the equation would need a constant. But all the letters in the equation can be varied

(edited 7 years ago)

Reply 2082

DesignPredator

9

Original post by lucabrasi98

Either your 5a is wrong or the AQA text book is wrong. Because the text book says induced emf is EQUAL to rate of change of flux linkage. Not proportional. Plus if it was proportional then the equation would need a constant. But all the letters in the equation can be varied

Both will be accepted as seen from previous mark schemes and there is a constant, that is -1.

Reply 2083

Datta10

3

Original post by DesignPredator

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) No external forces

bi) V=mv/N

bii) Derivation

ci) 216
ii) 1.15x10^-19 kgms-1 OR Ns
iii) 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.

For 5b, I put emf induced in coil by accident , I think the question was out of 3, would I get at least 1 for saying change in disk rotates, so change in flux ?

Reply 2084

lucabrasi98

15

Original post by DesignPredator

Both will be accepted as seen from previous mark schemes and there is a constant, that is -1.

B,A,N and T can all be varied. A constant is something like G in the equation for gravitational firled strenth. The -1 isn't really a constant, it's just essentially demonstrating Lenz's law. It implies they're in opposite directions. And IIRC you had to mention lenz' law later in the question.

I don't recall any mark schemes where they accept both but maybe you're right

(edited 7 years ago)

Reply 2085

C0balt

16

Im pretty sure one of the mark schemes said it was proportional

Reply 2086

mcride98

1

What if I said Faraday's law was emf is proportional to rate of change of flux, and not flux linkage? (constant of proportionality would be N, number of turns)

Will I lose any marks?

(edited 7 years ago)

Reply 2087

particlestudent

13

Original post by mcride98

What if I said Faraday's law was emf is proportional to rate of change of flux, and not flux linkage? (constant of proportionality would be N, number of turns)

Will I lose any marks?

Not sure, I may have said that too :frown:

. To make things even worse, I said the induced emf is proportional to the rate of change of flux with time :angry:

Reply 2088

Aprkrheiqkk

1

Original post by DesignPredator

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) No external forces

bi) V=mv/N

bii) Derivation

ci) 216
ii) 1.15x10^-19 kgms-1 OR Ns
iii) 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.

Cheers! I can't remember all my answers now but I recall getting a lot of similar answers. Do you remember what question 4(a) asked?

Reply 2089

lfcrules

2

Hey @cobalt, noticed you have an offer for natsci at cambridge , which college????

Reply 2090

Aprkrheiqkk

1

Was the question which proceeded the energy proof asking to calculate the momentum of the alpha particle. If so, does anyone remember their working out for it?