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

1. The way I did it was work out the length of the sting using g=9.81 and T=1.42 on Earth.
Then using the same equation but instead of g=9.81 use g=(9.81 x 0.37)

should give you length = 0.501
and T on Mars = 2.33 s
2. Guys what is magnetic flux linkage?
3. Can anyone just give me a list of topics that come up as the essay questions??
4. (Original post by sophieo128)
Guys what is magnetic flux linkage?
It is the magnetic flux density perpendicular to the area A

=BAN
5. please could someone explain how to do these questions? thanks.

Q13. Water of density 1000 kg m–3 flows out of a garden hose of cross-sectional area 7.2 × 10–4 m2 at a rate of 2.0 × 10–4 m3 per second. How much momentum is carried by the water leaving the hose per second?
A 5.6 × 10–5 N s
B 5.6 × 10–2 N s
C 0.20 N s
D 0.72 N s (
6. (Original post by Charlie1523)
Can anyone help me with his question:

Which of the following statements is true for a rectangular coil rotating in a uniform magnetic field?

A: The magnitude of the induced EMF is greates when the coil is parallel to the field
B: Increasing the frequency of rotation increases the max EMF
C: The induced Emf is independant of the area of the coil
D: A graph of Emf/time would be linear

I know B is definetly true but I also thought A was true? thanks
A is wrong because emf is greatest when the coil is right-angled to the field-lines
7. (Original post by Music With Rocks)
It is the magnetic flux density perpendicular to the area A

=BAN
thank you
so how does that come into transformers or electromagnetic induction?
8. (Original post by Mentalmirz)
please could someone explain how to do these questions? thanks.

Q13. Water of density 1000 kg m–3 flows out of a garden hose of cross-sectional area 7.2 × 10–4 m2 at a rate of 2.0 × 10–4 m3 per second. How much momentum is carried by the water leaving the hose per second?
A 5.6 × 10–5 N s
B 5.6 × 10–2 N s
C 0.20 N s
D 0.72 N s (
length = volume / area
length = (2.0x10-4)/(7.2x10-4)
length = (5/18) m
length per second is equivalent to a velocity
v = (5/18) ms-1

mass = volume x density
mass = 1000(2.0x10-4)
mass = 0.2 kg
m = (1/5) kg

therefore using p = mv
p = (1/5) x (5/18)
p = 1/18
p = 0.056 kg ms-1
Hey, just a general question, think it'd be better to begin section B first rather than A? Spend an hour on section B and the rest on A?
idk, ive tried both in past papers and neither really affected how long it took me. i usually start with A as a nice warm up tbh.
10. (Original post by ReeceFraser)
Can somebody go through the 6 marker from Jan 2012, i literally have no idea.
The ac current in the coil produces an alternating magnetic field, which is concentrated in the iron rod and passes through the ring. This changing magnetic field induces an emf in the ring. Because the ring is aluminium it is a good conductor and the emf causes a large current in it. A current-carrying conductor in a magnetic field experiences a force so this current produces a magnetic field whose direction opposes the applied field. Interaction between these fields gives a net upwards repulsion of the ring. As the ring moves upwards the magnetic field becomes weaker and the force on the ring decreases. The ring’s position becomes stable when the upwards magnetic force balances its weight.

From examiners report...This is the "ideal" answer
11. (Original post by Charlie1523)
Can anyone help me with his question:

Which of the following statements is true for a rectangular coil rotating in a uniform magnetic field?

A: The magnitude of the induced EMF is greates when the coil is parallel to the field
B: Increasing the frequency of rotation increases the max EMF
C: The induced Emf is independant of the area of the coil
D: A graph of Emf/time would be linear

I know B is definetly true but I also thought A was true? thanks
The RATE of change of flux linkage is max when the coils are parallel with the field lines
12. yo, do we use 9.81 or 9.8 for g?
13. (Original post by doshea1311)
idk, ive tried both in past papers and neither really affected how long it took me. i usually start with A as a nice warm up tbh.
Ya I start with A too. It builds your confidence and you feel more prepared for B.
14. (Original post by Anon-)
yo, do we use 9.81 or 9.8 for g?
9.81 it is in the formula book.
15. Is anyone else completely screwed? Ive tried a few past papers today and couldnt even do half... I couldnt bring myself to grade them :/
16. (Original post by alevelstresss)
length = volume / area
length = (2.0x10-4)/(7.2x10-4)
length = (5/18) m
length per second is equivalent to a velocity
v = (5/18) ms-1

mass = volume x density
mass = 1000(2.0x10-4)
mass = 0.2 kg
m = (1/5) kg

therefore using p = mv
p = (1/5) x (5/18)
p = 1/18
p = 0.056 kg ms-1
cheers
17. From Jan 2012.
18. (Original post by sophieo128)
thank you
so how does that come into transformers or electromagnetic induction?
Faradays law of electromagnetic induction: the induced emf in a circuit is equal to the rate of change of flux linkage through the circuit.

when the magnetic field is perpendicular to the coil area MAX flux linkage

When the magnetic field is parallel to the coil area MIN flux linkage (Zero)
The RATE of change of flux linkage is max when the coils are parallel with the field lines
Are you sure it's not when they are perpendicular to the field? Induced emf is directly proportional to rate of change of mag flux linkage
20. I'm guessing a 6 marker on SHM is due... Probably something to do with damping / resonance or a calculation based one

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