# AQA GCSE Physics Unit 3 (P3) Unofficial Markscheme

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#1
I know there are a few semi-started threads but none of them seem to have got anywhere, so here's a slightly more complete one. Feel free to reply with corrections / anything I missed.

Q1. Using the motor effect to create a loudspeaker
1a) State two variables the student should control (q states that the student is investigating how changing the size of the current affects the distance moved)

- Strength of the magnet
- Number of coils of the magnet

(Possibly also things like the thickness of the wire?)
1bi) How much does the distance change?
2.7cm - 1.4cm = 1.3cm

1bii) State two conclusions you can make from the graph

- Increasing the current increases the distance moved
- A current greater than 1.0A has no further effect (distance does not increase)

Q2 - Vision defects and correction

It would allow people to focus on objects that are different distances away

b) Explain how the human eye forms an image

- Light enters the eye via the pupil, the size of which is controlled by the iris.
- Most light is focussed by the cornea, which is a convex lens
- The light focusses due to refraction (spotted on the FA paper somebody had said diffraction)
- Light is then focussed further by the lens
- The thickness of the lens is adjusted by the ciliary muscles and suspensory ligaments
- Possible credit for explaining how this takes place
- Light is focussed onto the retina, which then transfers this information to the brain via the optic nerve.
- When a person is short-sighted their focus light "short of the retina"
- This is because their eyeball is too long or the eye lens is too strong
- Possible credit for saying that this can be corrected with a diverging lens or laser eye surgery.
-Short sight is caused by eyeballs being too long and eye lens being too strong. - Possible credit for saying this can he corrected with a converging lens or laser eye surgery.

Really hard to say for these QWC questions what the breakdown of marks will be like. I'd imagine 2 for a simple description (lens / cornea focus light), 2 more for talking about SL/CM and how they change the shape of the lens and the final 2 for long sight and short sight.

Q3. CT scans are used to create 3D images

3ai) How does a CT scan increase the risk of cancer? (2 marks)

- CT scans use X-rays
- To get a 3D image you need to use multiple X-rays so it's a higher exposure
- X-rays are highly ionising and may damage DNA

3aii) Why still carried out? (1 mark)

- Because the risk of cancern is smaller than the risk of the illness that the patient already has / because the information is too valuable.

3b) Precautions taken by mother (1 mark)

- Stand behind a protective screen

3c) State one advantage of using CT scans rather than ultrasound

- Higher resolution image due to shorter wavelength of X-ray vs sound wave

Q4 - Digital cameras

a) Name of light detector

- CCD / Charge coupled device

b) Types of images formed using converging and diverging lenses

Converging: Both real (if >F) and Virtual (If <F)
Diverging: Virtual only

c) Describe three differences between the refractive index of the glass used in C and D lenses

1. RI of converging lens is always higher than diverging lense
2. Maximum RI occurs at different frequencies (760 x blah for converging and 790 ish for diverging)
3. Difference in RI is bigger for converging than diverging

4d) Calculate the angle of refraction when the angle of incidence is 20 and the RI is 1.6

RI = sin i / sin r
1.6 = sin 20 / sin r
sin r = sin 20 / 1.6 = 0.342 / 1.6
sin r = 0.214
r = sin-1 (0.214) = 12.34 degrees

4e) Focal length is 40cm. Calculate the power. Give the unit (3 marks)

Convert focal length to metres --> 0.4
Power = 1 / f = 1 / 0.4 = 2.5
Power of a diverging lens is always negative so answer = -2.5 Dioptres

4f) Two factors that affect the power of the lens

- Material
- Curvature of the glass

Q5 - Jaws of life

5a) State the property of liquids...

Virtually incompressible

5b) Pressure = 5.2 x 10^8 Pa
Cross-sectional area = 4.1 x 10^-4m^2
Calculate the force at the load Piston to 2 SF

P = F / a
5.2 x 10^8 = F / 4.1 x 10^-4

5.2 x 10^8 * 4.1 x 10^-4 = F
F = 213200 N
To 2 s.f. this is 210000N

5c) ??

5d) The moments of the forces on the jaws are in equilibrium. Explain what is meant by this.

- Clockwise moment = Anticlockwise moment
- Therefore there is no resultant moment

Q6 - Balancing potato

ai) Cross in the centre of the potato

aii) State the meaning of CoM

Point where the mass appears to be concentrated

6b) Time for half an oscillation is 0.4s. Calculate f

Whole oscillation = 0.8s
F = 1/0.8s = 1.25 Hertz

Q7 - Ultrasound

a) What is the minimum frequency of ultrasound? (1 mark)
20,001 Hertz

bi) What measurement do you need to find the distance of the crack? (1 mark)
- The time between the transmitter and the crack

bii) What other information is needed to calculate the answer? (1 mark)
- Speed of sound

biii)What happens when the ultrasound reaches the crack? (2 marks)

- The ultrasound is partially reflected at the interface between the two media

(I guess one mark for reflected and one for partial?)

7c) An aircraft can fly for 2000 hours after a crack develops. The wing is tested every 500 hours. If a crack is found it is replaced. If there is a crack the ultrasound test works 99% of the time.

Suggest why the interval between tests is less than the safe flying time after a crack develops

- Multiple opportunities to find the crack (i.e. should be tested 3 times between crack developing and being unsafe)

Q8 - Train

a) Explain how the train can be accelerating while moving at a constant speed?

- Acceleration is change in velocity
- Velocity is a vector: it includes speed and direction
- The direction of the train is constantly changing as it accelerates towards the centre of the circle

b) The tilting train is designed so the line of action is always between the two rails. Suggest why the train does not topple

- The train base is always smaller than the rails, so the line of action does not come outside of the base and there is no resultant moment.

c) Explain why the engineer is correct that the relationship is inversely proportional

- As Angle of tilt increases, minimum safe radius decreases
- As angle doubles (e.g. 2-->4) minimum radius halves (e.g. 3000 --> 1500)
0
3 years ago
#2
(Original post by Cirsium)
I know there are a few semi-started threads but none of them seem to have got anywhere, so here's a slightly more complete one. Feel free to reply with corrections / anything I missed.

Q1. Using the motor effect to create a loudspeaker
1a) State two variables the student should control (q states that the student is investigating how changing the size of the current affects the distance moved)

- Strength of the magnet
- Number of coils of the magnet

(Possibly also things like the thickness of the wire?)
1bi) How much does the distance change?
2.7cm - 1.4cm = 1.3cm

1bii) State two conclusions you can make from the graph

- Increasing the current increases the distance moved
- A current greater than 1.0A has no further effect (distance does not increase)

Q2 - Vision defects and correction

It would allow people to focus on objects that are different distances away

b) Explain how the human eye forms an image

- Light enters the eye via the pupil, the size of which is controlled by the iris.
- Most light is focussed by the cornea, which is a convex lens
- The light focusses due to refraction (spotted on the FA paper somebody had said diffraction)
- Light is then focussed further by the lens
- The thickness of the lens is adjusted by the ciliary muscles and suspensory ligaments
- Possible credit for explaining how this takes place
- Light is focussed onto the retina, which then transfers this information to the brain via the optic nerve.
- When a person is short-sighted their focus light "short of the retina"
- This is because their eyeball is too long or the eye lens is too strong
- Possible credit for saying that this can be corrected with a diverging lens or laser eye surgery.
-Short sight is caused by eyeballs being too long and eye lens being too strong. - Possible credit for saying this can he corrected with a converging lens or laser eye surgery.

Really hard to say for these QWC questions what the breakdown of marks will be like. I'd imagine 2 for a simple description (lens / cornea focus light), 2 more for talking about SL/CM and how they change the shape of the lens and the final 2 for long sight and short sight.

Q3. CT scans are used to create 3D images

3ai) How does a CT scan increase the risk of cancer? (2 marks)

- CT scans use X-rays
- To get a 3D image you need to use multiple X-rays so it's a higher exposure
- X-rays are highly ionising and may damage DNA

3aii) Why still carried out? (1 mark)

- Because the risk of cancern is smaller than the risk of the illness that the patient already has / because the information is too valuable.

3b) Precautions taken by mother (1 mark)

- Stand behind a protective screen

3c) State one advantage of using CT scans rather than ultrasound

- Higher resolution image due to shorter wavelength of X-ray vs sound wave

Q4 - Digital cameras

a) Name of light detector

- CCD / Charge coupled device

b) Types of images formed using converging and diverging lenses

Converging: Both real (if >F) and Virtual (If <F)
Diverging: Virtual only

c) Describe three differences between the refractive index of the glass used in C and D lenses

1. RI of converging lens is always higher than diverging lense
2. Maximum RI occurs at different frequencies (760 x blah for converging and 790 ish for diverging)
3. Difference in RI is bigger for converging than diverging

4d) Calculate the angle of refraction when the angle of incidence is 20 and the RI is 1.6

RI = sin i / sin r
1.6 = sin 20 / sin r
sin r = sin 20 / 1.6 = 0.342 / 1.6
sin r = 0.214
r = sin-1 (0.214) = 12.34 degrees

4e) Focal length is 40cm. Calculate the power. Give the unit (3 marks)

Convert focal length to metres --> 0.4
Power = 1 / f = 1 / 0.4 = 2.5
Power of a diverging lens is always negative so answer = -2.5 Dioptres

4f) Two factors that affect the power of the lens

- Material
- Curvature of the glass

Q5 - Jaws of life

5a) State the property of liquids...

Virtually incompressible

5b) Pressure = 5.2 x 10^8 Pa
Cross-sectional area = 4.1 x 10^-4m^2
Calculate the force at the load Piston to 2 SF

P = F / a
5.2 x 10^8 = F / 4.1 x 10^-4

5.2 x 10^8 * 4.1 x 10^-4 = F
F = 213200 N
To 2 s.f. this is 210000N

5c) ??

5d) The moments of the forces on the jaws are in equilibrium. Explain what is meant by this.

- Clockwise moment = Anticlockwise moment
- Therefore there is no resultant moment

Q6 - Balancing potato

ai) Cross in the centre of the potato

aii) State the meaning of CoM

Point where the mass appears to be concentrated

6b) Time for half an oscillation is 0.4s. Calculate f

Whole oscillation = 0.8s
F = 1/0.8s = 1.25 Hertz

Q7 - Ultrasound

a) What is the minimum frequency of ultrasound? (1 mark)
20,001 Hertz

bi) What measurement do you need to find the distance of the crack? (1 mark)
- The time between the transmitter and the crack

bii) What other information is needed to calculate the answer? (1 mark)
- Speed of sound

biii)What happens when the ultrasound reaches the crack? (2 marks)

- The ultrasound is partially reflected at the interface between the two media

(I guess one mark for reflected and one for partial?)

7c) An aircraft can fly for 2000 hours after a crack develops. The wing is tested every 500 hours. If a crack is found it is replaced. If there is a crack the ultrasound test works 99% of the time.

Suggest why the interval between tests is less than the safe flying time after a crack develops

- Multiple opportunities to find the crack (i.e. should be tested 3 times between crack developing and being unsafe)

Q8 - Train

a) Explain how the train can be accelerating while moving at a constant speed?

- Acceleration is change in velocity
- Velocity is a vector: it includes speed and direction
- The direction of the train is constantly changing as it accelerates towards the centre of the circle

b) The tilting train is designed so the line of action is always between the two rails. Suggest why the train does not topple

- The train base is always smaller than the rails, so the line of action does not come outside of the base and there is no resultant moment.

c) Explain why the engineer is correct that the relationship is inversely proportional

- As Angle of tilt increases, minimum safe radius decreases
- As angle doubles (e.g. 2-->4) minimum radius halves (e.g. 3000 --> 1500)
You my friends are a genius
0
#3
(Original post by mn9011)
You my friends are a genius
You misspelled teacher :-D
0
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