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1

Refractive index

n =sini/sinr

2

Critical angle

1/sin(C)

sin x = n2/n1
n2 being lower number

3

State the difference between polarised and non-polarised light.

Single wavelength/frequency (1)
Waves in antiphase superimpose giving complete or partial cancellation (1)

4

What quantity is represented by the horizontal axis of the trace? (ultrasound)

1. Time (1)

5

Explain briefly how the two peaks of the trace are formed. (ultrasound\)

Reflections occur at boundary between head and surrounding fluid
(1)
1st reflection entering head, 2nd reflection on leaving (1)

6

Explain briefly how the trace could be used to obtain a measurement of the size of the baby’s head.

Time between peaks found from trace (1)
Knowing speed of ultra sound, ν in head, distance can be calculated l = ut (1)
Width of head = l/2 (1)

7

Explain what is meant by the term Doppler shift.

A change in frequency (1)
caused by relative movement between transducer and object

8

Calculation of time between emission and detection of radar pulse:

2s /c (1)
=2×6.0×107 m÷3.0×108 ms–1 =0.4s(1)

9

Speed of ultrasound Use of υ

Speed of ultrasound Use of υ = s/t (1)

10

State one way in which the oscilloscope trace will change when the ultrasound probe is above the obstruction.
..................

Change of trace Extra pulse(s) OR
Reflected pulse moves closer

11

After the obstruction has been cleared, a “Doppler” ultrasound probe is used to measure the speed of the soup in the pipe. Describe the principle of this method.

What must be measured to determine the speed of the soup? ............................................................................................................................................... ...............................................................................................................................................
(1)
Someone says that this would be easier if the soup contained lumps like vegetables. Comment on this suggestion.

3 points from:
• Arrange probe so that soup is approaching
• Soup reflects ultrasound
• with changed frequency/wavelength
• change in frequency/wavelength depends on speed
• Probe detects frequency of reflected ultrasound Use of diagrams showing waves
Determination of speed
1 point from:
• Frequency/wavelength change
Angle between ultrasound direction and direction of flow of soup Comment
Lumps give larger reflections
Lumps travel slower

12

What quantity is represented by the horizontal axis of the trace? (ultrasound)

1. Time (1)

13

Explain briefly how the two peaks of the trace are formed.

Reflections occur at boundary between head and surrounding fluid
(1)
1st reflection entering head, 2nd reflection on leaving (1)

14

There are concerns among fishermen that dwindling fish stocks in the world’s oceans are result a of modern fishing, techniques. Fishing trawlers can detect shoals of fish using ultrasound.
Describe the movement of water molecules when an ultrasound wave passes.

Movement of water molecules Molecules oscillate/vibrate (1) Movement parallel to energy flow (1)

15

Ultrasound pulses can be transmitted into the sea and the reflected waves can be detected and used to find the position of a shoal of fish.
Explain why pulses of ultrasound are used.

To prevent interference between transmitted and reflected signals (1) OR allow time for reflection before next pulse transmitted

16

A shoal of fish is at a depth of 300 m. Calculate the time interval between transmitting the pulse and receiving its echo.
(The speed of ultrasound in water = 1500 m s–1.)

Time for pulse to travel to fish and back again = distance ÷ speed
∆t = ∆x υ
= 2×300m (1) 1500ms−1
= 0.4 s (1)
[0.2 s = 1 mark]

17

A continuous ultrasound signal can be used to determine the speed of the shoal of fish. Name the effect used in this method.

Doppler effect (1)

18

Briefly explain the physics principles of this effect.(D}OPPLER)

a change in frequency of the signal
• caused by relative movement between the source and the observer
• size and sign of change relate to the relative speed and direction of the
movement between shoal and transmitter
• frequency increase - moving towards
• frequency decrease - moving away (1) (1)

19

How can you tell that the left peak represents the emitted pulse?

Emitted pulse
Greater amplitude/pulse is larger/taller (1)

20

Calculate the depth of the rail using a measurement from the oscilloscope trace.

Depth of rail
2d=vt=5100ms–1 ×4.8×10–5 s
= 0.24 m
Hence d = 0.12 m
Reading from graph [4.8 or 48 only] (1)
Calculation of 2d [their reading × timebase × 5 100] (1) Halving their distance (1)

21

The probe is now moved to another position on the rail where there is a crack one third of the way down from the top.
Rail Crack
Describe how the oscilloscope trace will change.

A reflected peak closer to emitted/now 3 pulses (1) Exact position e.g. 1.6 cm from emitted (1)

22

5.
Full-body CT scans produce detailed 3-D information about a patient and can identify cancers at an early stage in their development.
(a) Describe how a CT scan image is produced, referring to the physics principles involved.


• X-ray source + detectors round patient ...
• ... rotated around patient .../ the signal / X-ray passes through the same section of the body from different directions.
• ... producing a (thin) slice / cross-section.
• Idea of absorption / less gets through / more is absorbed ...
• by dense material / bone / material of high Z / High Z related to materials such as bone / Low Z to materials such as soft tissue
• attenuation is by the photo-electric effect
• the possibility of using a contrast medium.
• better than a simple X-ray at differentiating other organs.
• patient is moved a small distance and the process is repeated / process continues in a spiral.
• a computer (analyses the data) / identifies the position of organ/bone ...
• ... and forms a 3-D image.
6. (i)
• 5.4 cm +/– 0.1 cm read from the graph (1)
–1 3–1
• =5.4×20μscm ×1.5×10 ms (1)
• = 0.162 m (1)
• 0.162/2=0.081mor8.1cm(1)

23

7. Discuss briefly the advantages and disadvantages of scanning using MRI techniques.

7. Any six from:
method does not use ionising radiation
hence no radiation hazard to patient or staff
gives better soft tissue contrast than CT scans
generates data from a 3D volume simultaneously
information can be displayed on a screen as a section in any direction
there are no moving mechanisms involved in MRI
There is no sensation, after effects at the field strengths used for routine diagnosis Strong magnetic field could draw steel objects into the magnet
Metallic objects may become heated
Cardiac pacemakers may be affected by the magnetic fields
CT scanners better for viewing bony structures

24

8. Explain how ultrasound is produced using a piezoelectric crystal such as quartz.

alternating voltage or alternating E-field across crystal (1)
at resonant frequency (1) allow reference to resonance of crystal

25


9. Describe the use of a contrast medium, such as barium, in the imaging of internal body structures. Your answer should include
• how an image of an internal body structure is produced from an X-ray beam
• an explanation of the use of a contrast medium
• examples of the types of structure that can be imaged by this process.


9. Formation of image to a max 3 e.g.
X-rays are detected by a film / scintillation counter etc., (1)
High ‘Z’ means high attenuation / low transmission
[Allow atomic mass / nucleon number] (1)
shadow on the film / reference to exposure after attenuation (1) Reference to photoelectric effect / energy range around 1–100keV /
absorption ∞ Z3 (1)
Explanation of the use of a contrast medium to a max.4 e.g.
X-rays do not differentiate / show up soft tissues well ...(1)
... as similar absorption / ‘Z’ is similar / ‘Z’ is low for these tissues. (1) Contrast medium has high ‘Z’ / absorbs X-rays strongly.(1)
It is usually taken orally / as an enema / can be injected.(1)
Example of type of structure that can be imaged to a max.1 e.g.
digestive tract / throat / stomach.(1)
B1 × 6
2
[6]
[2]
to a max. 8

26

Name and state the function of the parts labelled A, B, C and D.- part of the ear

ear drum [or tympanic membrane] (1) transfers sound waves from the outer ear to the ossicles of the middle ear (1)
2. (a)
coherent bundle:
fibres maintained in fixed positions relative to each other (1) non-coherent bundle:
fibres have no fixed relative positions (1)
PhysicsAndMathsTutor.com
1
B ossicles [or bones of the middle ear] (1)
system of levers with a mechanical advantage (of 1.5) [or amplification] [or which links two membranes (ear drum and oval window)
or transmits sound vibrations from outer to inner ear] (1)
C windows: oval and round (1)
allow sound vibrations to enter the fluid of the inner ear
[or allows sound vibrations to be transmitted around the cochlea
or contain the inner ear's fluid while allowing the fluid to move] (1)
D cochlea (1)
convert (pressure) waves [or vibrations] in the fluid into electrical signals [or stimulates (auditory) nerves to send signals to the brain] (1)

27

Bundles of optical fibres are described as either coherent or non-coherent.
(a) Describe how the fibres are arranged in each type of bundle and explain how the different
designs determine their optical characteristics.

coherent bundle:
fibres maintained in fixed positions relative to each other (1) non-coherent bundle:
fibres have no fixed relative positions (1)

28

State an application for each type of bundle.
application of coherent bundle ................................................................................... ................................................................................. .................................................... application of non-coherent bundle ........................................................................... .....................................................................................................................................

coherent bundles of fibres transmit images (of internal organs of the body) (1)
non-coherent bundles transmit (or conduct) light (to inside the human body for illumination) (1)
2
2

29

Label and describe parts of x ray tube

glass tube (1)
(sealed), evacuated, allows electrons to travel unimpeded (1)
B rotating anode [or target] (1)
rotation of anode [or target] to spread heated area (1)
target which emits X-rays when hit by (energetic) electrons (1)
C filament [or cathode] (1)
heat source to release electrons from surface of cathode by thermionic emission (1)
D lead housing (1)
prevent X-rays from escaping in unwanted directions (1)

30

The threshold of hearing is quoted as 1.0 × 10–l2W m–2. Explain what is meant by the threshold of hearing and state the frequency at which the threshold has this value.

lowest level of sound (intensity) which the ear can detect (1)
1 kHz (1)