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# Edexcel Physics IGCSE 1P Unofficial Mark Scheme 25th May 2016

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1. Tell me the questions which I'm missing out - I'll add them in. Please try your best to remember the rough question number. Thanks for all the contributions, including Advait10.

Do any of you remember which question they gave you a figure of 250000km or something like that. I'm trying to think of it but I can't remember. Tag me if you can remember it.

Do the poll!

1.a)
Constant velocity with horizontal line. (1)

1.b)
Distance travelled is area under line. (1)

1.c)
Average velocity is distance moved / time taken. (1)

2.a)
Coolant to reduce energy.Shielding to absorb radiation.Fuel rods for Uranium fuel. (2)

2.b)
Kinetic energy. (1)

2.c)
The purpose of the moderator is to slow down fast moving neutrons to become slow moving thermal neutrons. This makes it easier for neighbouring uranium nuclei to absorb the neutrons and hence go under fission. (2)

2.d)
A controlled chain reaction where only 1 out of 3 (on average) of the neutrons emitted through fission are absorbed by neighbouring uranium nuclei. This is helped by using boron control rods to absorb these remaining neutrons. This prevents an uncontrolled chain reaction. The neutron which is absorbed by a uranium nucleus becomes unstable hence splits into 2 daughter nuclei and 2-3 fast moving neutrons. This process keeps repeating. (3)

2.e)
Draw week 6 position of complete. (1)

2.f)
X between comet and Earth. (1)

2.g)
The distance from 1-3 is is roughly the same. 3-4 is increase in displacement. 4-5 distance decreases. Time is the same so change in displacement = change in speed as s = d/t.

2.h)
Orbits are closet to each other at 9. (1)

2.g)
Orbital speed = 150,000,000 * 2 * pi = 94247796.
1km365 * 24 = 8760so divide the first by the second to get 107588.7895km/hroughly equal to 108000km/h. (3)

3.a)
Pressure is P1V1 = P2V2 so: (101*1700)/12 = 14308.3kPa. (3)

3.b)
Pressure with depth = height x density x g. (1)

3.c)
113.08kPa. (3)

3.d)
113.08 + 101 = 214.08kPa. (1)

3.e)
Bubbles get larger as they rise due to the decrease in pressure with the decrease in depth as pressure = hpg, so air expands into larger volume. Also, smaller bubbles join together to form larger bubbles. (2)

4.a)
Gamma for tracing.X-rays for internal objects.Microwaves for food. (3)

4.b)
Particles carrying the energy (vibrations) travel perpendicular to the direction of the wave in motion. (1)

4.c)
You have to half the time because the time measured was for the wave travelling to the point of reflection and back as the sound wave travelled double the distance (to what you are measuring) so to get the depth from the point of emission to reflection, the time is divided by 2. (2)

4.d)
As v = frequency x wavelength, upon entering a denser medium the speed of sound increases as the wavelength increases. (2)

5.a)
Draw voltmeter parallel to LDR. (1)

6.a)
DC current is current that flows in one direction. (1)

6.b)
You can measure resistance by taking voltmeter reading (ensure it is constant) and ammeter reading and then do R = V/I (Ohms). (2)

6.c)
Graph. (4)

6.b)
The purpose for the split ring commutator and carbon brushes is so that once the coil goes past the half turn, when the coil retouches the commutator the direction of the current reverses hence magnetic field hence the effect of the force on the coil, ensuring it travels unidirectionally. (3)

6.c)
The coil continues to rotate clockwise. (1)

7.a)
Refractive index in glass is higher than air. YES
If i = 0, the ray doesn't deviate. YES
All rays that enter are totally internally reflected. NO (4)

7.b)
Draw point on graph. (1)

7.c)
It fits with correlation and gradient of graph as point is plotted above point following. (1)

7.d)
Refractive index can't be 0, only <1. (1)
Critical angle can't be 0. (1)

7.e)
Critical angle was 41.82 so rounds to 42. (3)

7.f)
Refractive index is the simplest ratio between speed of light in air: speed of light in material medium. (2)

7.g)
Draw rays and arrows. (4)

8.a)
Ruler. (1)

8.b)
Hooke's law: Measure length of spring using ruler. Add 1N mass, measure new length, subtract original length from this to get extension. Repeat this process for a range of masses. Repeat whole experiment x3 and average for increased reliability. Plot graph of extension vs load, if follows Hooke's law, the gradient line between points will be contrast as F = ke (extension is proportional to the load). (5)

9.a)
5.3 cm. (2)

9.b)
5.12cm (1)

9.c)
Differing results.
String measurements are to 0.1 cm.
Digital measurements are to 2 decimal places.
String measurements are averaged.
Digital only takes 1 measurement.
String measurement subject to parallax error due to human judgement.
Calliper more accurate.
Calliper measures diameter.
String measures circumference. (4)

10.a)
P = IV (1)

10.b)
Max power = (4000*600)/1000000 = 2.4 MJ. (2)

10.c)
Work done = Force x distance

10.d)
76000000J of energy. (3)

10.d)
35.02 seconds. (2)

10.e)
Decreasing power increases time taken for the same amount of work done. (1)

11.a)
KE = 1/2 x m x v(squared). (1)

11.b)
Velocity = 12m/s. (3)

11.c)
GPE = mxgxh. (1)

11.d)
GPE is gained as the lift moves up from platform to surface hence increase in height hence increase in GPE. (2)

11.e)
Slope up causes transfer of KE to GPE hence decrease in velocity hence deceleration hence less work required by brakes. Slope down converts GPE into KE hence increase in speed hence acceleration hence less work required by motor. Energy is conserved. (4)

12.a)
Sky has lowest temperature and snow and bear have same temperature which is warmer. (2)

12.b)
Hair acts as an insulator by trapping in a pocket of air, hence preventing heat loss via convection as convection requires for the movement of gas particles. (2)

12.c)
Snow was best at reflecting, worst at absorbing. Sky and polar bear good at absorbing, bad at reflecting. (2)

12.d)
UV is not reflected by the sky, it is absorbed. (1)

12.e)
Hence with white fur on top, it increases the surface area of the fur exposed to the air, minimising loss of thermal energy via radiation. By having the black skin underneath, it limits heat loss via radiation and any heat that is radiated is reflected back by fur hence retaining heat. (4)

12.f)
UV waves don't reach skin as they are good absorbers, bad reflectors hence do not undergo total internal reflection hence doesn't reach skin. (3)
2. the exam was brutal, my god
3. 2b.) kinetic energy
2c.) asked what a moderator does
2d.) asled to explain in terms on neutrons what a controlled nuclear fission is (something like that)
4. I think moderators slow down neutrons so that they can be absorbed by Uranium 235.
5. 3- the question matching up the uses of electromagnetic waves in hospitals

x-rays-imaging broken bones
microwaves- heat up patients food
gamma?
6. (Original post by niv1234)
I think moderators slow down neutrons so that they can be absorbed by Uranium 235.
No, I think its so they don't get absorbed by Uranium isotopes. Moderators slow down neutrons so they are at the right speed to perform nuclear fission

Posted from TSR Mobile
7. What did people get for the polar bear one? The bear was dark so it had lots of UV in/on it, does that mean it reflected it or absorbed it? Loads of people got different answers for this so I wasn't sure
8. (Original post by niv1234)
3- the question matching up the uses of electromagnetic waves in hospitals

x-rays-imaging broken bones
microwaves- heat up patients food
gamma?
Thanks, yeah its right, I'm just talking about that with my friend.
9. [QUOTE=pk789;65164835]No, I think its so they don't get absorbed by Uranium isotopes. Moderators slow down neutrons so they are at the right speed to perform nuclear fission

Yes, thats what I meant sorry I didn't explain clearly enough. I meant as in if the neutrons were made to go slower by the moderators, it would be easier for them to be absorbed by Uranium-235 so nuclear fission can happen.
10. (Original post by escg)
the exam was brutal, my god
Really? Quite a few found it to be in my school but I found it quite usual.
11. Question on why refractive index doesnt have a unit, why there is not 0 value for it on the graph,
12. Also someone else has made one
http://www.thestudentroom.co.uk/show....php?t=4118285
13. (Original post by amarjoshi99)
There was a question on what is the pressure after diving 10m and then next q was "what is this value with the atmospheric pressure (105) which I got answer 14308+105= 14413
I believe you needed to convert it to KPa
14. (Original post by amarjoshi99)
Question on why refractive index doesnt have a unit, why there is not 0 value for it on the graph,
i said because the critical angle can't be zero and neither can the refractive index but I'm not sure if thats right
15. Test was hard, more so than any other past paper that i did
16. That exam was the worst i mean who puts a question about polar bears???
Really? Quite a few found it to be in my school but I found it quite usual.
smartest girl in my year, scored 100% on every past paper came out of the exam in near tears. all the boys were complaining lol. may the grade boundaries be really low for this.
19. ugh that diver q with the pressure equation...please tell me other people didn't get the right equation
20. Was the LDR at the top of the circuit or at the bottom? I put it at the bottom at first but changed it..

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