Unofficial AQA Physics Unit 3 GCSE NEW SPEC Mark Scheme

1.

.
[2]

2.

Iris [1] May allow Pupil
Ciliary muscles changes shape (width) of eye lens [1]
Eye lens focuses light onto the retina [1]

3.

As age increases, near point increases (near point is further away from eye): at 10 years near point was 10cm while at 40 years it was 25cm. [2]

4.

A larger sample size could be used (more than 4 people) and mean near points could be worked out. [1]

5.

Power= 1/Focal Length= 1/(40cm/100)= 1/0.4m= 2.5 Diopters [2]

1.

Design A is more stable as it has a wider base and lower centre of mass. [2]

2.

Ray diagram of 3 rays with arrows showing direction [4]

3.

The camera image can be described as real and inverted. [2] Allow diminished

1.

Ultrasound is above the human hearing range which is 20Hz to 20000Hz. Therefore, ultrasound is beyond 20000 Hz. They are non-ionising but are partially reflected at the boundary of tissues of two different densities. The reflected waves are detected by the transmitter and a computer builds an image. They can be used to detect different tissues but are not useful in producing an image of bone. Meanwhile, X-rays waves are high frequency and have a short wavelength. They are also ionising, having no safe limit. This can cause cell mutation and lead to cancer. They are absorbed by dense materials, such as bone, but pass through tissues. X-rays expose a film or CCD to produce an image. Bones are white as these areas are not exposed. This allows fractures to be seen clearly. [6]

2.

X-rays are ionising and could harm the unborn child by causing cell mutation leading to cancerous growths. [2]

3.

One medical use of ultrasound is to destroy kidney stones. [1]

1.

The property that all liquids are virtually incompressible. [1]

OR

The property of all liquids are that pressure acts equally in all directions. [1]
.

2.

Force exerted by master piston is 84N. Must show working out and correct use of following formula: Pressure (N/m²)= Force (N) x Area (m) [2]

3.

Force F of the master piston is smaller than the force exerted by the slave pistons since hydraulic systems are force multipliers. [2] Allow use of data

1.

Centripetal force [1]
The force is towards the centre of the G-machine. [1] Allow towards the centre of the circle of motion

2.

As speed increases, size of the force on the astronaut increases. [1]
As radius of the G-machine decreases, size of the force on the astronaut increases. [1]
Deceasing the radius of the G-machine has more effect on the force than increasing the speed [1]

3.

The change of force between 20m/s to 40m/s is: 40m/s-20m/s= 16000N-4000N= 12000N [1]

4.

The current through the wire creates a magnetic field which interacts or repels the magnetic field of the permanent magnets. Therefore, a force is applied on the wire.

5.

Side A: Force is ↓
Side C: Force is ↑ [1]

6.

Side B experiences no force as the wire is parallel to the magnetic field lines of the permanent magnets. [1]

7.

The operators change increase the strength of the permanent magnets. [1] Allow increase number of turns in coil or increase current in wire

8.

Yes, space exploration produces many technological advancements that can be used elsewhere. [1]

OR

No, space exploration is a waste of money that could be used in areas that directly benefit humans such as healthcare and medicine. [1]

Allow acceptable reasons to justify choice

1.

Moment= Force x Distance → Force= (Moment/Distance)= (36Nm/0.6m)= 60N [2]

2.

The bag topples as there is a resultant clockwise moment- the resultant moment is not zero. This is due to the line of action of the weight being outside the base of the bag. [2]

3.

Frequency= 1/Time Period = 1/(160 secs/10 swings)= 1/16= 0.0625Hz [3]

1.

The alternating current in the first coil produces an alternating or changing magnetic field. This magnetic field is increased by the iron core. The second coil cuts magnetic field lines as the magnetic field changes. This induces an alternating potential difference. If the circuit is complete, an alternating current will flow through the second coil. [3]

2.

Potential difference the charger supplies to the laptop is 20 V. Must show working out and correct use of following formula: (Primary Potential Difference/Secondary Potential Difference) = (Primary Turns in Coil/Secondary Turns in Coil) [2]

3.

Current in the primary coil is 0.3 A Must show working out and correct use of following formula: Primary Current (Amps) x Primary Potential Difference (Volts) = Secondary Current (Amps) x Secondary Potential Difference (Volts0 [2]

4.

Another advantage of a switch-mode transformer is that it can be used with high frequencies (50000Hz to 200000Hz). [1]

OR

Another advantage of a switch-mode transformer is that it wastes little energy when not in use. [1]
.

5.

An advantage of these batteries is that they would have a longer life and, so, would not need to be replaced as often which would be useful in areas where replacement batteries are not readily available. [1]