Physics G491 Jan 13, Advancing physics/physics B exam thread

Am I the only 'girl' here? Now I understand why this test was hard for me. They should give extra 2 marks to any girls sitting this crazy paper. Haha. #


I kid ^_^

I think that our paper was harder than Jan 10. Anyone else think the same?

What was the question about the distance of lens ?

Which resistance did you put circle around?

250 ohms for resistance I put. Does anyone have an unoffical markscheme that someone coul post?

Which resistance did you put circle around?

I also put that, but it was kind of a guess. How sure are you?

The very first question? The waves were coming in with 0 curvature. Curvature =1/u. Since 1/u = 0, u = ∞ (object is really far away). I think if you just said the waves had zero curvature, that'd be enough for the mark.

I also put that, but it was kind of a guess. How sure are you?

1. As, JC-1 , AV-1 (3)
2i) Wave-fronts are parallel before the lens (1)
ii) Focusing waves at focus (1) wave-fronts equally spaced by eye (1)
3i.) 250 ohms (1)
ii) 0.048A (2) ecf from i)
4a) 77Hz (1)/ find highest frequency and divide by 5 as uncertainty divided by 5 too (1)
5a) 225 MPa (1)
ii) 2.25 x1011 Pa (2)
b) Amplitude decreased (1), same frequency (1)/ by same scale factor (1)
6a) 3000 bits-1 (3)
b) Analogue signal rounded to nearest voltage level (1)
c) Increase amount of bits/ sample (1) so there are more voltage levels to round to (1)
7. 0.06m (2)
Another part to this question???
8a) 0.0348A (2)
ii) 5,000,000 Hz (1)
ii) 4 (1)
b) 53.3s (2)
ii) Bits/s decreases due to (other file downloading) (1) means takes longer to download desired amount of bits (1)
c) Amount of noise increases with distance (1)/ after 60m noise too much (1) / reference to low Vtotal/Vnoise ratio (1)/ digitising just copies noise (1)/ less waves hit the laptop directly from a distance (1) / interference from other waves (1) Max (4)
9a) Ductile- can be drawn into wires/ can be stretched with plastic deformation (1) carbon atoms pin dislocations into place in steel (1)/ dislocations allow a few planes of atoms to slip in pure iron causing ductility (1)
b)i) Difficult to scratch/dent (1) tip would become blunt (1)
ii) Negative sea of electrons glues positive metal ions together by electrostatic forces (1) covalent bond is sharing of electrons (doubtful mark, certainly wouldn’t need the full covalent bond saga), bonding non-directional in steel/ directional in diamond (1) covalent bonds are (very) strong (1), reference to no slip/ plastic flow/ dislocation in diamond (1) Max (4)
10a) So that conductive layer can bend and complete the circuit (1)
ii) So circuit is not automatically completed (1)
b) i) More conductive than an insulator but less conductive that a conductor (at room temperature) (1)
ii) Reference to doping (1) more free electrons (1) Max (1) for heat up with explanation
c) As X moves to the right, resistance of left resistor increases (1), so Vout increases (1)
d)i) Show 12/60 x 1000 = 20mVmm-1 (1)
ii) 0.25mm (1)
iii) 60/0.25 = 240 (1) , 27 < 240 < 28 (1), so 8 bits needed (1)

I said the waves were parallel to each other, would this get the mark?

1. As, JC-1 , AV-1 (3)
2i) Wave-fronts are parallel before the lens (1)
ii) Focusing waves at focus (1) wave-fronts equally spaced by eye (1)
3i.) 250 ohms (1)
ii) 0.048A (2) ecf from i)
4a) 77Hz (1)/ find highest frequency and divide by 5 as uncertainty divided by 5 too (1)
5a) 225 MPa (1)
ii) 2.25 x1011 Pa (2)
b) Amplitude decreased (1), same frequency (1)/ by same scale factor (1)
6a) 3000 bits-1 (3)
b) Analogue signal rounded to nearest voltage level (1)
c) Increase amount of bits/ sample (1) so there are more voltage levels to round to (1)
7. 0.06m (2)
Another part to this question???
8a) 0.0348A (2)
ii) 5,000,000 Hz (1)
ii) 4 (1)
b) 53.3s (2)
ii) Bits/s decreases due to (other file downloading) (1) means takes longer to download desired amount of bits (1)
c) Amount of noise increases with distance (1)/ after 60m noise too much (1) / reference to low Vtotal/Vnoise ratio (1)/ digitising just copies noise (1)/ less waves hit the laptop directly from a distance (1) / interference from other waves (1) Max (4)
9a) Ductile- can be drawn into wires/ can be stretched with plastic deformation (1) carbon atoms pin dislocations into place in steel (1)/ dislocations allow a few planes of atoms to slip in pure iron causing ductility (1)
b)i) Difficult to scratch/dent (1) tip would become blunt (1)
ii) Negative sea of electrons glues positive metal ions together by electrostatic forces (1) covalent bond is sharing of electrons (doubtful mark, certainly wouldn’t need the full covalent bond saga), bonding non-directional in steel/ directional in diamond (1) covalent bonds are (very) strong (1), reference to no slip/ plastic flow/ dislocation in diamond (1) Max (4)
10a) So that conductive layer can bend and complete the circuit (1)
ii) So circuit is not automatically completed (1)
b) i) More conductive than an insulator but less conductive that a conductor (at room temperature) (1)
ii) Reference to doping (1) more free electrons (1) Max (1) for heat up with explanation
c) As X moves to the right, resistance of left resistor increases (1), so Vout increases (1)
d)i) Show 12/60 x 1000 = 20mVmm-1 (1)
ii) 0.25mm (1)
iii) 60/0.25 = 240 (1) , 27 < 240 < 28 (1), so 8 bits needed (1)