X Rays, CT Scans and Ultrasound

a) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also refer to the information in the Marking guidance, and apply a ‘best-fit’ approach to the marking.

0 marks No relevant / correct content.

Level 1 (1-2 marks) There is a basic description of either wave OR What happens to either wave when they enter the body. However there is little other detail.

Level 2 (3-4 marks) There is either: A clear description of BOTH waves OR A clear description as to what happens to BOTH waves inside the body OR A clear description of ONE of the waves with clear detail as to what happens to either wave inside the body.

Level 3 (5-6 marks) There is a detailed description of BOTH of the waves AND

A detailed description as to what happens to EITHER wave inside the body.

Examples of the points made in the response:

Description of an X-ray

• X-rays are electromagnetic waves / part of the electromagnetic spectrum

do not allow a description of a property – eg X-rays travel

• X-rays are (very) high frequency (waves)

through a vacuum / at the speed of light

• X-rays are (very) high energy (waves)

• X-rays have a (very) short wavelength

• Wavelength (of X-rays) is of a similar size to (the diameter of) an atom

• X-rays are a transverse wave

correct description acceptable – oscillations / vibrations are perpendicular (at 90°) to direction of energy transfer

• X-rays are ionising radiation

Description of ultrasound

• ultrasound has a frequency above 20 000 (hertz)

or

ultra sound is above 20 000 hertz

• ultrasound is above / beyond the human (upper) limit (of hearing)

accept ultrasound cannot be heard by humans

• ultrasound is a longitudinal wave

correct description acceptable – oscillations / vibrations (of particles) are parallel (in same direction) to direction of energy transfer

Statement(s) as to what happens to X-rays inside the human body:

• X-rays are absorbed by bone

• X-rays travel through / are transmitted by tissue / skin

Statement as to what happens to ultrasound inside body:

• ultrasound is (partially) reflected at / when it meets a boundary between two different media

• travel at different speeds through different media

6

(b) (because the X-rays) are ionising

accept a description of what ionising is

1

(they will) damage cells

instead of cell, any of these words can be used:

DNA / genes / chromosomes / nucleus

or

mutate cells / cause mutations / increase chances of mutations

or

turn cells cancerous / produce abnormal growths / produce rapidly growing cells

do not accept they can be dangerous (to human health)

do not accept damage to soft tissue

or

kill cells

1

idea that X-rays cause mutations

gains 1 mark

but X-rays can cause/increase chance of mutations

gains 2 marks

mutations usually harmful/produce abnormal growth serious effect on growing foetus/rapidly growing cells

each for 1 mark [4]

a) X-rays are ionising or X-rays kill / damage cells

accept cause cancer 1

any stray X-rays are absorbed by screen 1

which reduces the radiation dose to the radiographer 1

(a) any two from:

• (sound with frequency) above 20 000 hertz / 20 kHz

• frequencies above (human) audible range

• (sound) cannot be heard by humans 2

(c) any one from:

• removal / destruction of kidney / gall stones

• repair of damaged tissue / muscle

accept examples of repair, eg alleviating bruising, repair scar damage, ligament / tendon damage, joint inflammation

accept physiotherapy

accept curing prostate cancer or killing prostate cancer cells

• removing plaque from teeth

cleaning teeth is insufficient

1

(b) 640

an answer of 1280 gains 2 marks

allow 2 marks for the correct substitution

ie 1600 × 0.40 provided no subsequent step

allow 2 marks for the substitution

provided no subsequent step

allow 1 mark for the substitution 1600 × 0.80 provided no subsequent step

allow 1 mark for the identification that time (boat to bed) is 0.4 3

(a) (i) J and L

both required, either order 1

(ii) K 1

(iii) L 1

highest frequency

reason does not score if L not chosen

accept most waves (on screen)

do not accept frequency above 20 000(Hz)

do not accept cannot hear it 1

(d) advantage

any one from: • (images are) high quality or detailed or high resolution

clearer / better image is sufficient

• (scan) produces a slice through the body • image can be viewed from any direction

allow images are (always) 3D / 360°

• an image can be made of any part (inside the body)

allow whole body can be scanned • easier to diagnose or see a problem (on the image)

1

disadvantage

any one from: • (the X-rays used or scans) are ionising

allow a description of what ionising is • mutate cells or cause mutations or increase chances of mutations

allow for cells:

DNA / genes / chromosomes / nucleus / tissue • turn cells cancerous or produce abnormal growths or produce rapidly growing cells • kill cells

damage cells is insufficient • shielding is needed

can be dangerous (to human health) unqualified, is insufficient 1

(c) a CT scan gives a 3D image 1

therefore the image can be observed from different directions 1

The Eye

(i)

award 1 mark for each correct label 4

b) iris or pupil 1

to change the shape / curvature (of the surface) of the lens

accept to make the lens thinner / fatter

to contract and relax is insufficient 1

to focus the light (from the object, onto the retina)

accept to refract / change direction of light

accept rays for light

accept to form / focus an image (on the retina)

to focus is insufficient

1

(c) (i) short sight

or

myopia

accept near sight 1

(ii)

any 2 correct construction lines:

construction lines may be dotted or solid

construction lines must pass correctly through the lens

treat more than 2 construction lines as a list for marking 2

upright image drawn at correct location

image must be to the left of the lens

upright orientation of image must be clear

the image line can be dotted or solid ignore any arrows on construction rays

1

(d) to focus light from objects at different distances

accept can see objects (clearly) at different distances.

to focus light on the retina is insufficient 1

Lenses

(b) any two correct construction lines:

if more than 2 construction lines treat as a list 2

• line passing straight through centre of lens (& out other side)

• line travelling parallel to principal axis & then being refracted through principal focus (on RHS)

• line travelling through principal focus (on LHS) & then being refracted to be parallel to principal axis (on RHS)

inverted image drawn (with arrow) in correct location 1

one arrowhead from object to image on any construction ray

conflicting arrowheads negate this mark

1

(c) any two from:

• inverted

accept upside down

• real

• diminished / smaller

allow ecf if ray diagram wrongly drawn but descriptions must relate to their image

a converse negates mark, eg real and virtual scores zero 2

(a) (i) two correct rays drawn

1 mark for each correct ray

• ray parallel to axis from top of object and refracted through focus and traced back beyond object

• ray through centre of lens and traced back beyond object

• ray joining top of object to focus on left of lens taken to the lens refracted parallel to axis and traced back parallel to axis beyond object

2

an arrow showing the position and correct orientation of the image for their rays

to gain this mark, the arrow must go from the intersection of the traced-back rays to the axis and the image must be on the same side of the lens as the object and above the axis

1

(ii) (x) 3.0

accept 3.0 to 3.5 inclusive or

correctly calculated

allow 1 mark for correct substitution into equation using their figures

ignore any units 2

(b) any two from:

in a camera the image is:

• real not virtual

• inverted and not upright

accept upside down for inverted

• diminished and not magnified

accept smaller and bigger accept converse answers but it must be clear the direction of the comparison

both parts of each marking point are required 2

(b) 2 lines correctly drawn from the top of the pin through the lens

allow 1 mark for each 2

position of image correct

image must be upright 1

(b) (the image) needs to fall on film / sensors / LDRs / CCDs

accept just ‘charged couples’ do not credit ‘… solar cells’ do not accept virtual image cannot be stored

1

either to cause a (chemical) reaction or to be digitalised

for credit response must be appropriate to camera type 1

object (should be) on the far side of F / the focus (from the lens)

or … more than the focal length (away from the lens) allow ‘beyond the focus’

or object should be more than twice the distance / 2F (from the lens) (2 marks)

or … more than twice the focal length (away from the lens) (2 marks)

1

Refraction

a) (i) line drawn at 90 degrees to the normal:

ignore (partial) reflection of the ray 1

(ii) 1.5

award both marks for an answer that rounds to 1.5

award 1 mark for correct substitution ie 1 / sin 41 or 1 / 0.656(059)

2

(b) 26

award 3 marks for an answer that rounds to 26

award 2 marks for

1.3 =

or

r = sin -1(0.57(3576) / 1.3)

award 1 mark for correct substitution.ie 1.3 =

or

sin 35° shown correctly, ie 0.57(3576), or used correctly in the calculation

an answer of 0.44 scores 2 marks

an answer of 26.9 scores 0 3

(a) because the angle of incidence is greater than critical angle

accept the light is totally internally reflected 1

(b) 41.8

allow 1 mark for correct substitution, eg 1.5 =

or

sin c =

or

c = sin-1 2

Centre of Mass and Moments

(a) (i) turning

accept turning ringed in the box 1

(ii) point at which mass (or weight) may be thought to be concentrated

accept the point from which the weight appears to act

allow focused for concentrated

do not accept most / some of the mass

do not accept region / area for point 1

(b) 600 (Nm)

400 × 1.5 gains 1 mark provided no subsequent steps shown 2

(c) (i) plank rotates clockwise

accept girl moves downwards

do not accept rotates to the right 1

(total) CM > (total) ACM

accept moment is larger on the girl’s side 1

weight of see-saw provides CM

answer must be in terms of moment

maximum of 2 marks if there is no reference to the weight of the see-saw

1

(ii) W = 445 (N)

W × 1.5 = (270 × 0.25) + (300 × 2.0) gains 2 marks

allow for 1 mark:

total CM = total ACM either stated or implied

or

(270 × 0.25) + (300 × 2.0)

if no other marks given 3

[10]

(a) 60

allow 1 mark for correct substitution (with d in metres), ie 36 = F × 0.6

an answer of 0.6 or 6 gains 1 mark 2

(b) the line of action of the weight lies outside the base / bottom (of the bag)

accept line of action of the weight acts through the side

accept the weight (of the bag) acts outside the base / bottom (of the bag)

1

a resultant / overall / unbalanced moment acts (on the bag)

accept the bag is not in equilibrium

do not accept the bag is unbalanced 1

(b) any two from:

• make (the area of) wheels bigger

• make wheels wider apart

• make suitcase shorter but wider

Shorter handle 2

(c) 0.0625

allow 1 mark for correct substitution, ie 16 =

an answer of 0.00625 gains 1 mark 2

hertz / Hz

do not accept HZ or hz 1

[7]

Hydraulics

(a) hydraulic (system) 1

(b) 15.40 ×102 or 1540

allow 1 mark for correct substitution, ie

8.75 × 104 =

or

87 500 =

or

F = 8.75 × 104 × 1.76 ×10-2

or

F = 87 500 × 0.0176 2

(c) (i) downward force produces pressure in liquid

reference to compression of liquid negates this mark 1

this pressure is the same at all points in a liquid or this pressure is transmitted equally through the liquid

and P = F / A or F = P × A 1

area (at load) bigger (so force bigger) 1

Circular Motion

(a) the direction of the riders is constantly changing 1

therefore the velocity of the riders is changing 1

and because acceleration is the rate of change of velocity the acceleration is changing

1

(b) to(wards) the centre (of the cylinder / rotor) 1

(b) centripetal 1

(b) it is reduced 1

d)

an increase in the speed of rotation an increase in the total mass of the wheel, the capsules and the passengers.

the greater the radius / diameter / circumference (of the wheel)

the smaller the (resultant) force (required)

accept ‘the size’

both parts required for the mark

accept converse 1

v) speed constant (1) mass constant (1)

for 1 mark each 2

Transformers

a) (i)

1

1

1

1

(a) an alternating input / current to primary (coil) 1

which produces an alternating magnetic field

accept changing magnetic field for alternating magnetic field

if first mark point scores then ‘alternating’ not required here 1

in the (iron) core

this magnetic field links with the secondary coil 1

which induces an (alternating) voltage / p.d. across the secondary (coil)

(ii) 16 000

allow 1 mark for correct substitution

ie 400 ÷ 25 = n ÷ 1000 2

(c) (i) need a.c. 1

battery is d.c. 1

i) any one from:

do not accept any response in terms of heat insulation, safety or electric shock

• (so that there is) no short circuit

• (so that the) current goes around the coil

do not accept electricity for current

• (so that the) current does not enter the core 1

(ii) (easily) magnetised (and demagnetised)

accept ‘(it’s) magnetic’ do not accept ‘because it’s a conductor’

1

(iii) p.d. increased (by transformer at power station)

do not accept energy increased 1

so current decreases 1

this reduces energy / power loss (in cables)

allow heat for energy

allow increases the efficiency

do not accept no energy losses 1

The Motor Effect

(a) motor 1

(b) (i) wire kicks further (forward)

accept moves for kicks

accept moves more

accept ‘force (on the wire) increased’ 1

(ii) wire kicks back(wards) / into (the space in) the (horseshoe) magnet

accept moves for kicks

accept ‘direction of force reversed’ 1

(b) smaller / lighter 1

uses little power / energy 1

when left switched on with no load applied

dependent on second marking point 1