Physics Flashcards

(61 cards)

1
Q

Refractive index

A

n =sini/sinr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Critical angle

A

1/sin(C)

sin x = n2/n1
n2 being lower number

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

State the difference between polarised and non-polarised light.

A

Single wavelength/frequency (1)

Waves in antiphase superimpose giving complete or partial cancellation (1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

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

A
  1. Time (1)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

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

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain what is meant by the term Doppler shift.

A

A change in frequency (1)

caused by relative movement between transducer and object

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Calculation of time between emission and detection of radar pulse:

A

2s /c (1)

=2×6.0×107 m÷3.0×108 ms–1 =0.4s(1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Speed of ultrasound Use of υ

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

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

A

Change of trace Extra pulse(s) OR

Reflected pulse moves closer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

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.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

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

A
  1. Time (1)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

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.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

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.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

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.)

A
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]
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

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

A

Doppler effect (1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

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

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

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

A

Emitted pulse

Greater amplitude/pulse is larger/taller (1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

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

A
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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

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

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

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.

A

• 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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q
  1. Discuss briefly the advantages and disadvantages of scanning using MRI techniques.
A
  1. 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q
  1. Explain how ultrasound is produced using a piezoelectric crystal such as quartz.
A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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) ```
31
Sound intensity levels are usually measured in decibels. Give two reasons why this logarithmic scale is used.
ear has a logarithmic response [or log scale chosen to match (perceived) response of the ear] (*) to accommodate very wide range of sound intensities to which ear can respond (*) perceived change in loudness is proportional to fractional change in intensity (*) 10- fold increases in intensity are perceived as steps of equal increase in loudness (*) log scale means that numerical values on the scale represent ratios of two sounds, expressed as the log of that ratio (*) (*) any two (1) (1)
32
Why was it necessary to introduce an adapted scale referred to as the dBA scale, which is used on some sound level matters?
the dBA scale takes account of the frequency dependence of the sensitivity of the ear [or to match the ear’s frequency response or meters calibrated on a dBA scale give frequency-weighted readings] (1)
33
Modern hi-fi equipment and televisions often have volume controls which allow the sound volume to be increased in steps. If each of these steps produces an increase in the sound intensity level of 2.0 dB, calculate (i) the ratio by which the sound intensity is increased for each step up in volume, ...................................................................................................................
2.0 = 10log  I  (1) 1 I2 = 1.58 (1) I1
34
State and explain whether the following changes in the optical fibre would increase or decrease the probability of light escaping from the fibre. (i) increasing the refractive index of the cladding bending the fibre into a tighter curve
smaller difference between the core index and cladding index makes critical angle larger (1) therefore increases the chance of light escaping (1) makes internal angle of incidence at core-cladding interface more likely to be less than the critical angle (1) therefore increases the chance of light escaping (1)
35
Explain how a piezoelectric crystal is caused to generate waves of ultrasound.
two faces of a thin slice of crystal (coated with a thin layer of silver) act as electrodes (1) electrodes connected to high frequency (several MHz) source of e.m.f. (1) as applied e.m.f. alternates it applies alternating (rapidly reversing direction) electric field across the slice of crystal between the electrodes (1) crystal expands and contracts at the same frequency as the applied e.m.f. (1) the vibrations of the faces of the crystal slice produce ultrasound pressure waves (1) [8]
36
(b) In medical applications of ultrasound a short pulse of duration about 1 s is often used. (i) Explain why the pulse of ultrasound must be short.
pulse short compared with the transit time (1) pulses are used for timing echoes which give measurements of depth in the body (1) pulse must be short enough to ensure the leading edge returns after the trailing edge departs (1)
37
(ii) Short voltage pulses applied to the piezoelectric crystal make it vibrate and emit short pulses only if the crystal assembly is modified. Explain the modification which is necessary.
behind the crystal a vibration-absorbing backing material is attached (1) this stops the vibrations quickly after the electrical signal is stopped, ensuring that the pulse is short (1)
38
Under what conditions is ultrasound reflected strongly at boundaries between two types of material? ........................................................................................................................... ...............................
when there is a large difference in acoustic impedance [or significant change in density or significant change in elasticity or texture of tissue] (1)
39
State two physical properties of the materials which determine the proportion of ultrasound which is reflected at a boundary. ........................................................................................................................... ...........................................................................................................................
) tissue density (1) | tissue elasticity/texture (1)
40
Explain what a coupling medium or gel is and why, and where, it is used. ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................
ultrasound is reflected back at boundaries with air [or replacement of air prevents reflection] (*) gel between transducer and skin (prevents loss of signal due to boundary reflection) (*) acoustically well -matched gel gives good transmission (with minimum reflection at skin boundary) (*) (*) any two (1) (1)
41
(a) Describe the practical process, including details of the use of the transducer and the adjustment of the oscilloscope, required to produce this A-scan.
surface of body covered with an oil to improve transmission from ultrasound transducer to body (1) short ultrasound pulses sent into the body and echoes received from surfaces detected by the transducer (1) 5 [12] oscilloscope sweep time synchronised with the ultrasound pulse frequency (1)
42
(a) Explain why the spectrum has | (i) a maximum photon energy and state the circumstances in which a photon of this energy is produced,
maximum photon energy determined by accelerating voltage (1) corresponds to all electron kinetic energy (1) converted to single photon (1) only one electron can contribute to production of X-ray photon (1)
43
State what is meant by the threshold of hearing and state the frequency at which the reference threshold is quoted.
threshold of hearing – lowest intensity of sound detected by human ear (1) reference intensity (1.0 × 10–12 W m–2) is taken at 1 kHz (1)
44
Astigmatism is caused by
astigmatism usually caused by an irregularity in the curvature of the cornea (
45
The image seen by a person with astigmatism is .............................................. ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................
a person with astigmatism would see an image which was less well-focussed in one particular plane [direction] (1)
46
(iii) Astigmatism is corrected using ........................................................................
defect is corrected using a (correctly orientated) cylindrical lens (1)
47
refractive index using speed
ci/cr
48
refractive index
sini/sinr
49
lens formula
p 1/f = 1/u + 1/v when working out u is ideal , v is what it is, negative to left of lens to get lens strength 1/ f in metres
50
intensity level
db = 10 log (I)/(Io)
51
calculate activity
``` a = lander N a = Aoe ^ -lander t ```
52
Calculate number of undecayed uncle
N= Noe^ - ladner t
53
Activity
lander times number of undecided nuclei
54
calculate decay constant
0.693/ half life
55
intensity of collimated x ray
I = Ioe ^ xu x is thickness u is coefficient
56
Reflected intensity
(Z2 - Z1 )/( Z2+Z1) squared (entire equation )
57
Ads and Dis of MRi
``` does not use ionising radiation no risk of damage for patient / staff gives better soft tissue contrast than CT scan 3D image disadvantages strong magnetic field could draw steel objects metallic objects may be heated pacemakers affected CT better for bone ```
58
Experiment for radiation types Alpha beta gamma xray
Alpha- use paper screen to block source - measure shcnage Beta- use source of aluminium
59
Differences between Alpha and Beta
penetration low- alpha opposite for beta | ionisation high - alpha opposite for beta
60
Differences between gamma X-ray
gamma energy high | x ray energy low
61
MRI
hydrogen atoms in body hav prescession beucase unequal number of protons and neutrons this will be either parallel or antiparallel thhey are all mini magnets mri creates large magneti field around patient protons line up radiowaves passed through patient if the radio frequency matches the larmor frequency the protons will flip relaxation time is how long it takes for protons to return to original precession relaxation time varies for different tissue types paramagnetic substances can be used as contrast materials they will generate a small magnetic field that causes relaxation time to shorten therefore, a greater contrast image is produced mri can create 3d image allows preceise location of injury to be found good for brain scans and finding soft tissue tumours however, there is no ionising radiation with mri so no risk of cance