OCR Gateway Physics B - P4 P5 P6 - Unofficial Mark Scheme

Resultant velocity was 6 for X not Y I think.

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I thought it was an OR gate.

Thank you so much for making these!
For section D I got 4 people
1200J/s
240m^2

Is this right?

Also I got 0.45 s for the P5 6 marker?

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yep i got the voltage was 2.5 V for C and 200 V for D

) Explain the role of the relay [2]• a logic gate is a low power device that would be damaged if exposed directly to mains power (1)• the relay isolates the low voltage in the sensing circuit from the high voltage mains (1)

You know for this question. It asked about the logic gate and the bell. So I thought it was talking about how a small current is needed to switch on the circuit where a larger current flows to switch on the bell. As it wasn't talking about the mains electricity

Does anyone remember the Section D Questions?

How did you all get 1200, 2152 or whatever these dodgy answers are.
I got them all but I just made up my own formula.

I don't even understand how: 2J were lost in the first part - what is the formula, Power / (Area * Temperature)?

For the last question (area), I used the formula:

Uvalue = power / (area * temperature)

and rearranged it for area

Once I've finished C6, I will do section D

Thanks can u also tell me the questions. I fked up badly. I didn't realise that formula :/ I think I did in the exam but I thought it was wrong .
Especially for some questions lol.. I got (area + temperature) * power lol and all sorts of stuff.

I agree - it was so confusing!!

Just about to start section D after doing the p6 six marker so the questions and answers will be there

Thank you .

Hey, doesn't the graph get less steeper?
I know you mean if the resistance increases, since its the gradient.
But, the graph was already steep and if you increase the resistance by 3 times, the current will be smaller for a given voltage. So, the line will actually be less steep? Or, did I just interpret it incorrectly again lol.

EDIT: I just read it wrong, should've gone with my mathematical brain. ****, another question gone.

Sorry about that it's so hard under the pressure of exams but you still will have done really well - you seem really clever

OCR Gateway Physics B
P4 P5 P6 + Section D
Unofficial Mark Scheme
Wednesday 22 June 2016

Module P4 - 25 marks
1) Radiation treatment
a) Explain why an alpha source cannot be used as a tracer [1]
(too ionising and so) will not penetrate out of the skin (1)

b)i) Explain why a radioactive source should not remain in the body for a long time [1]
to not cause damage to healthy living cells (1)

b)ii) What is the name given to how long a source stays radioactive? [1]
half-life (1)

c) Radiation may be used to treat brain cancer - explain why the head should be clamped [2]
so that the gamma rays are focused on the tumour (1)
to avoid damage to non-cancerous / healthy tissue / cells (1)

2) Fuses and wiring [QWC 6]
Marking points
why only two wires are needed: it is double insulated and so the earth wire is not needed - even if the live wire becomes loose, the plastic cannot become live: maybe include purpose of live and neutral wires (to carry the voltage and complete the circuit respectively)

why a fuse is needed: too large a current causes the fuse to melt, preventing flow of current, which prevents flex overheating and causing fire - and prevents further damage to appliance

why a 13A fuse is used instead of 3A: operating current must be between 3A and 13A so that the fuse does not break under normal operation (this would happen for a 3A fuse), but also breaks if the current gets too high

3) Static electricity
a) Complete the sentence [1]
he gains a positive charge because he loses electrons (1)

b) Explain how anti-static sprays work [1]
make surface of object conductive (1)

c) Explain why the small strip attached to his car may be unreliable [1]
not touching the ground / not made of a conductor / easy to break off (1)

d) Describe and risk and benefit of the petrol filler [2]
risk: spark due to static charges which could cause an explosion (1)

benefit: quick to use as flows out quickly / does not build up as much charge as it flows out quickly / reduces the amount of time during which the car and pump are in contact, reducing explosion risk (1)

4) Nuclear radiation
a) Write the letters in order [2]
B, E, F, A

four correct (2)
two or three correct (1)
otherwise (1)

b) Explain the purpose of boron rods but explain why they need to be removed some times [2]
absorb excess neutrons to stop reaction going out of control (1)

(need to be removed so that) there are enough neutrons for the reaction to continue (1)

5) Power, current, resistance and voltage
a) Calculate the output voltage of the adapter [2]
94V (2)
incorrect answer with workings (1)

b) In which country will the iron have the highest electrical power? They all use the same current. Explain your answer [1]
Kenya, because it has the highest input voltage (1)

c) In Japan, the iron is bad at ironing out creases. She attaches a variable resistor and then it become better at ironing out creases. Explain why [2]
before, it had a low power as they all used the same current and it had the lowest input voltage (1)
variable resistor can be used to decrease resistance and increase current, making the power greater (1)

Module P5 - 25 marks
6) Boat/speeds
a) Difference between speed and velocity [1]
speed only has a magnitude while velocity has a magnitude and direction (1)

b) Which boat has the greatest resultant velocity? Why? [2]
there is a debate over this question, so I have put on both answers

boat X (1)
explanation involving resultant velocity (1)

or

boat Y (1)
explanation involving resultant velocity (1)

c) Calculate the speed of the horse [2]
example working (there may be other ways of doing it)
s = ((u + v) / 2) × t

t = 2s/(u + v) = 56 / 8 = 7 seconds

7 seconds (2)
incorrect answer with working (1)

7) Cars
a) Explain airbag release in terms of momentum [2]
change in momentum when the gas particles collide with the airbag walls and change velocity (1)
creating a force, creating a pressure (1)

allow use of equations

b) Calculate the speed of the car and if it was breaking the speed limit [3]
6.5m/s (2)
No (1) only if in relation to the answer for speed (no mark for 'No' without any other workings)

otherwise

working (1)

8) Waves and interference
a) Explain why the long wave radio waves have a long range [1]
not sure about this

any one of
diffraction around large objects (1)
and so can reach houses behind hills, for example (1)
reflection from ionosphere (1)

b) What are the properties of a wave needed for interference to occur [2]
(coherent wave source)

any two of
same wavelength (1)
same phase difference (1)
same amplitude (1)

c) Partial destructive interference can occur. Suggest why this happens and the result it may have [2]
not sure about this

any one of
waves partly in / out of phase (1)
phase difference of (n + 1/4)λ, for example (1)

and

the wave may have a partial loss in quality (e.g. sound loss in some areas) (1)

9) Dispersion/refraction
a) Explain why the red light refracts away from the normal [2]
passes over boundary between two media (glass and air) (1)
wave speeds up (so bends away from the normal) (1)

b) Explain why violet light refracts more [2]
higher refractive index (1)
wave speeds up more and so bends more (1)

10) Projectile motion [QWC 6]
Marking points
path: the horizontal velocity is unaffected by gravity - therefore the horizontal velocity is constant; gravity causes the vertical velocity to increase (constant vertical acceleration) - but not increasing vertical acceleration

calculation
s = ut + 1/2at^2

as the inital speed is 0, s = 1/2at^2

therefore, t^2 = 2s/a

therefore, t = √(2s/a) = √(2/10) = 0.447213595 = 0.4s, or 0.45s

Module P6 - 25 marks
11) Truth table / logic gates / relay
a) Complete the truth table [3]
D column correct (1)
E column correct (1)
Output column correct (1)

b) Explain the role of the relay [2]
• a logic gate is a low power device that would be damaged if exposed directly to mains power / high voltages (1)
• the relay isolates the low voltage in the sensing circuit from the high voltage (mains) (1)

12) Power transmission
a) Calculate the power loss in MW [2]
100^2 * 20 = 2000000W = 2MW

2MW (2)
2000000W (1)

b) Explain a risk and benefit of power transmission at high voltages [2]
risk: electrocution / any other suitable risk (1)
benefit: less power loss through heating of the cables (as lower current is needed) (1)

13) Transformers - which two columns were wrong and why? [2]
C, as wrong way round / use of calculation (1)

D, as wrong ratio / use of calculation (1)

14) Motors and magnetic fields
a) Draw the magnetic field around a solenoid [2]
field lines at top and bottom (1)
field lines at left and right sides (1)



b) What does reversing the current do to the magnetic field? [1]
(the magnetic field) reverses (1)

c) How can a motor be made to spin faster? [1]
any one of
• increasing the size of the electric current (1)
• increasing the number of turns on the coil (1)
• increasing the strength of the magnetic field (1)

15) Resistance graph
a) Calculate the resistance [2]
20Ω (2)
incorrect answer with workings (substitution of x and y values into R=V/I) (1)

b) What would happen to the gradient if the resistance value trebled? [2]
gradient would increase (get steeper) (1)
idea of gradient being (change in) y divided by (change in) x and comparison with R = V / I (1)

16) Potential divider with LDR [QWC 6]
Marking points
- when it gets dark, LDR resistance increases, increasing its share of the input voltage (and so increases the output voltage)

- when it gets very dark, LDR resistance increases so much that its share of the input voltage is nearly the entire input voltage, and so the output voltage can be said to be the input voltage (5V) - which is a logical 1 and so turns on the light

- contrast of above point with lighter conditions in terms of: logical 1 and 0, and resistance

Section D - 25 marks
17) Smith family in the UK (500kWh per person per day) use 730000kWH per year
a) Calculate the number of people in the Smith family [2]
730000 / 365 = 2000kWh per day

2000 / 500 = 4 people in the family

4 people (2)
incorrect answer with working (1)

b) Belgium uses more per person per day than the UK. Suggest why Belgium may have a lower electrical consumption than the UK overall [1]
lower population (1)

18) U-values
a) Calculate the energy lost per second with units [3]
2 × 12 × 50 = 1200J/s

either

1200 (2) incorrect answer with workings (1)

J/s (1) allow W

or

1.2 (2) incorrect answer with workings (1)

kJ/s (1) allow kW

b) Describe what would happen to energy transfer if the temperature difference increased [1]
(it would) increase (1)

c) Calculate the area of wall whose U-value was 0.5W/m²°C and the temperature difference along which was 12°C; 240J/s lost from the wall [3]
Uvalue = power / (temperature * area)

area = power / (temperature * Uvalue)

area = 240 / (12 * 0.5) = 40m²

40m² (3)
incorrect answer with all workings listed (2)
incorrect answer with some workings listed (1)

Final science exam done! (I break up on Friday though )

It was better than the P1 P2 P3 in my opinion but it was still difficult.

How did you all find it?