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OCR Physics B G492 Unofficial MARK SCHEME watch

1. Italics are question descriptions, not answers

Section A

1) Nm, Js^-1, kgms^-2 (3)
2) A, C, D (3)
3) Increase wavelength and distance from screen (2)
4) Photon energy
5) Double the wavelength, halve b (1)

6) Forces on a car
a) Magnitude = force forward - force backward. Direction = forwards (to the right) (2)
b) Power = Fv
c) a=F/m

Section B

7) Footballer
a) v=u+at
b) s=ut + 0.5at^2
c) drawing the velocity/time graph (4)

8) Standing waves
a) coherent waves reflect, superpose to form nodes of destructive interference, antinodes of constructive interference (3)
b) v=f x lamda
c) proving an equation (2)
d) describe another form of standing wave e.g. pipe with longitudinal waves

9) Light
a) both red and green light have maxima at 0th order so mix to create yellow colour
b)i) diffraction grating: 0.001/820 = 1.2x10^ -6
ii) using d=lamda sin(theta) to get same as above
c) show that sin(theta) > 1 (2)
d) Use E=hf to show that green light doesn't have enough energy at 2.1V to leave LED (4)

10)

Section C

11) a) sensitivity between 10-20 degrees (3)
5.6 for sensor A
2.4 for sensor B
Unit mV/0C

b) Sensor A: higher sensitivity over this range (1)
c) Sensor B: constant sensitivity over whole range (1)
d)

12)
a)i) Completing table
b) substituting gsin(theta) into v^2=u^2+2as
c)i) working out g: 27/2.8 = 9.6
ii) experimental factors affecting g (4)
Friction -> reduces g value
Air resistance -> reduces g
Average velocity recorded when card went through the light gate despite it accelerating
Underestimate of ramp length -> increases g value
Overestimate of ramp length -> decreases g value

13) a)i) 0.5s (or anything similar, it was an estimate of reaction time) (1)
ii) speed of light calculation (2)
iii) speed of light is very small fraction of reaction time so is unmeasurable. Can only say that light travels faster than 6.4km/s (using my values). (2)

b)i)
ii) small % uncertainty so small
iii)
iv) underestimated the uncertainty because the difference in values =118 which is much larger than 50 (2)

c)i) 1cm uncertainty from the drawing... (1)
ii) 2.94x10^8 with uncertainty of 0.49x10^8 (3)

Feel free to add/change, I can't remember much more!
2. I think 13ci was 1 mark, and 13 cii 2 marks.Question 1 was a total of 3 marks (1 for each correct answers), the same with question 2
3. (Original post by m00c0w)
.
Can you remember any of section a or b?
4. (Original post by Mabes)
Can you remember any of section a or b?
There was the question about the footballer in Section B. First question you had to use a suvat equation, then there was the question where you had to find the maximum acceleration, then there was a 4 mark question where you had to draw the velocity time graph of the ball
5. (Original post by Mabes)
Can you remember any of section a or b?
Red and green light both have maxima at the 0th order, so they mix to form a yellow colour.
Diffraction grating 0.001/819
Show sintheta > 1.
Showing, that energy provided by each electron is in between energies of the two colour waves.
6. There was another question in section c where you had to show that the acceleration =gsin(theta), then you had to show that the gradient of the line =2.8g
7. (Original post by Mabes)
Can you remember any of section a or b?
question 6 was about the forces acting on the car
part a) finding resultant force and direction - I said the direction was forwards and I can't remember the magnitude of force it was forward - backwards though
part b) can't remember
part c) finding acceleration with the force worked out in part a.
8. I don't think I remember getting A, C, D for Q2?
9. (Original post by gary96)
question 6 was about the forces acting on the car
part a) finding resultant force and direction - I said the direction was forwards and I can't remember the magnitude of force it was forward - backwards though
part b) can't remember
part c) finding acceleration with the force worked out in part a.
It was either 1500N or 1300N, can't remember which though.
B was the one where you had to find the power dissipated by the car at like 26m/s
In Section A there was a question where you had to find the number of photos emitted per second,
10. (Original post by m00c0w)
There was another question in section c where you had to show that the acceleration =gsin(theta), then you had to show that the gradient of the line =2.8g
for the second part:

v^2 = u^2 + 2as --> v^2/2s = a

a = gsin(theta)

v^2/2s = gsin(theta) ---> V^2/sin(theta) = 2sg

s= 1.4 so gradient, V^2/sin(theta) = 2.8g
11. (Original post by OldSchoolTech)
I don't think I remember getting A, C, D for Q2?
I think I got A, C and B.
12. (Original post by m00c0w)
It was either 1500N or 1300N, can't remember which though.
B was the one where you had to find the power dissipated by the car at like 26m/s
In Section A there was a question where you had to find the number of photos emitted per second,
I couldn't answer that one I had no idea what to do
13. (Original post by metaltron)
I think I got A, C and B.
the 3rd one was the one with energy and frequency right? I chose the one that looked like a recipricol graph
14. (Original post by gary96)
I couldn't answer that one I had no idea what to do
Which one? The power dissipated is just force*velocity
15. (Original post by gary96)
the 3rd one was the one with energy and frequency right? I chose the one that looked like a recipricol graph
I think I got A, C, D
16. (Original post by m00c0w)
Which one? The power dissipated is just force*velocity
photon one
17. (Original post by m00c0w)
I think I got A, C, D
From memory first one was linear, then quadratic, then reciprical.
18. (Original post by metaltron)
I think I got A, C and B.
A and C were straightforward enough.
I got D because the factor they changed by was constant.
19. (Original post by metaltron)
I think I got A, C and B.
i got C A B lol

**** that ****
20. For the power of the car one, it said power dissipated against resistive force: Does that mean you use the value of the force acting in the opposite direction to resultant? I think it was 5800N to the left?

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