AQA Physics A-Level 7408/2 Paper 2 Unofficial Markscheme threadWatch
1.31 grams for the mass of the rock before.
4.88x10 to the something for activity.
1.0) Question displays a hot tub containing 4.5 m^3 of water, which has a pump and heater in a loop adjacent to the tub.
The heater has a power output of 2.7kW.
1.1) Calculate the maximum temperature rise over 1hr caused by the heater.
Here I related Q=mc(dT) with the total power output of the heater in 1 hour.
(2700J * 60s * 60m), 9.72x10^6J
Relate this to Q=mc(dT) for a density of 1000kg per cubic metre giving 4500kg.
dT = Q / mc = 0.51K for me!
This seems unreasonable but I could not find another explanation so I kept it.
At a higher pumping speed, the temperature rise is greater over a time. Explain this assuming no loss of heat to surroundings.
I spoke about efficiency of the heater perhaps and the volume of water passing is greater.
2.0) This displays two charges, one of charge Q and one of +46 nC, 120mm apart from each other.
2.1) Definition of electric field strength.
2.2) At a point P that is 66mm right of charge Q, the electric field strength is 0, find the value of Q.
2.3) Must a net amount of work be done by bringing a charge to point P in the field from infinity?
I said no here as the overall electric field strength and thus potential is 0 at this point, so there is no NET change.
2.4) Displays a ball on a thread swinging and about to collide with a wall. Circular motion question.
Describe the motion of the ball if the string breaks.
Talk about how the velocity is always at a tangent to the circular path so it will go straight.
3.2) A charging circuit charging a capacitor has an emf of 9.8v at the power source and a resistor R in-line. The time constant of the capacitor is found to be 1.0s
Find the value of R in the circuit.
T = RC, 1 = R * 370uF,
So R must be 1/370x10^-6 = 2700 Ohms.
3.3) This had a graph so I cannot do much here, it displayed terminal p.d against time and asked for the voltage after 2.0s (I think???)
3.4) Calculate the time for the charging current to drop by half.
3.5) For charging, calculate the time for the capacitor to reach 3.0mC
Hi all I have quite a few questions and answers for the physics AQA paper 2 this morning, so I will post all of them here and we can begin to collaborate and form a full mark scheme hopefully! Kind Regards
4.2) A coil with the two ends routing into an ammeter to tell the current induced.
Left side of the coil was wire E and right of the ammeter is wire F.
A magnet with orientation (N------S) was put into the coil from the RIGHT side suddenly and then stopped. Describe the change on the ammeter.
4.3) How does the ammeter reading display the concept of Lenz's law?
4.4) A coil of 1 turn (length 32mm x 32mm even sides) in a uniform magnetic field (0.38T), was moved from inside the field to a point outside the field.
The maximum reading of emf induced was 2.9x10^-4, calculate the time taken in moving the coil outside the field.
Here I used magnitude of emf = N * (dFlux / dTime). To find flux use Flux = BA (flux density * area), and solve for time to find about 1.34s (perhaps?).
4.5) The coil is now rotated in the field and the maximum reading of voltage was 5.1mV, find the angular speed of the coil.
Again just finding area and using E = BANω to find the angular speed.
I got 13.1 rads-1 for my answer
5.1) What is the most likely source of radiation used to sterilize medical equipment to be used.
I said alpha as it is highly ionizing and harmful to tissue so will kill any organisms on it, probably wrong <_>
5.2) Why should we not be worried about the components becoming irradiated after this process?
I think I mentioned the short half life here and how exposure is reduced to minimum because of it
5.3) With aid of a calculation, explain why the results of detected activity of a source do not follow the inverse square law of radiation.
Distances: 0.2, 0.5, 1.0 and Activities: 9013, 1395 and 242 respectively
The constant of proportionality K was not constant in this so does not follow invrse sq. law.
5.4) Give two reasons why these results do not follow the inverse square law.
6.1) It had a graph again so I cannot be much help, you could find and use the half life to find the amount after 57s which for me was 2cm^3
Although there are probably a few routes of finding this
6.2) How could you model a decay of a substance with a greater number of nuclei?
Use greater vol of water
6.3) How could you model a decay with a smaller decay constant?
Use a smaller gap in the thin tube or tap to reduce flow
6.4) Calculate the half life of Rb in a sample. With a decay constant of 1.42x10^-11 years^-1
Sorry for missing information on the question here.
I got around 4.88x10^10 for this.
6.5) A sample of Rb has 1.23mg present now, how many grams were present 4.47x10^9 years ago?
I got around 1.07g for this but I will not post my method unless I find the answer to be right as it may be misleading (and foolish x-( )
6.6) Find the activity of the sample of 1.23mg of Rb
7.0) Nuclear decay
7.1) Draw a decay chain of two elements following an alpha, two beta minus(es), and an alpha decay.
Again a graphical question so not much help here x-(
7.2) There is an imbalance in the number of protons and neutrons in the nucleus of atoms.
Explain this imbalance using the fundamental forces experienced in the nucleus, and give ranges for which they are felt.
7.3) Show the decay of 205 - 82 Pb (Lead) by electron capture to 205 - 81 Tl (Thallium)
7.4) Tl is left in an excited state. Electromagnetic radiation is released from this decay process, state two sources of this radiation.
I said from the de-excitation of electrons releasing gamma photons, and not sure about the other but possibly infra-red from heat? (Perhaps this is also related to the excitation of electrons).
AND FINALLY! (No multiple choice here! Sorry x), I dont have that kind of patience on top of the time I had to complete this exam)
7.5) Why is 99 - 43 Tc (Technetium) safe to use in medical procedures.
I just wrote about how it is not an alpha emitter so does not cause a large number of ionisations, and that it has a short half life of around 6 Hours,
which reduces the exposure of the patient to a minimum.
Many thanks to all If I can't do well in physics, I'm dragging AQA down with me!
Good luck to all with your results.
Water moving faster in hot tub means more kinetic energy, so more internal energy and therefore heat, thermal energy transferred to water remained unchanged, that's all I could think of.