Notes-for-CAIE
Table of contents
- Telecommunication
- What is meant by
frequency modulation/amplitude modulation[2] - Why FM costs more than AM [2]
- What is meant by
noise[2] - What is meant by
attenuationof a signal [1] - What is meany by
bandwidthof signal [1] - Why regenerator amplifiers do not amplify the noise [2]
- Why use optic fibres than wire pair [3]
- Why use infra-red than visible light in optic fibres [2]
- Frequency range of waves [5]
- What is meant by
cross-talk/crosslinking[2] - Functions of the copper braid [2]
- Draw a diagram for coaxial cable [2]
- State three advantages of a coaxial cable compared with a wire pair [2]
- The principles of the geostationary satellite [4]
- The features of the geostationary orbit [2]
- Compare ionospheric reflection of radio than satellite communication [4]
- Why use frequencies of gigahertz for satellite communication [1]
- Why the uplink and downlink frequencies must be different [2]
- What is meant by an
analogue signal[1] - What is meant by a
digital signal[2] - Explain two advantages of the transmission of information in digital than analogue [4]
- Why base stations for mobile phone use high frequency [2]
- How to improve the quality of the received analogue signal (ADC-DAC) [4]
- Why neighbouring cells use different carrier frequencies (mobile phone) [1]
- Why each cell has a limited area (mobile phone) [1]
- Why cellular exchange always operates for the phone [3]
- Explain the purpose of the switch in the mobile phone circuitry [1]
- Explain the purpose of the parallel-to-serial converter [2]
- What is meant by
- Medical Physics
- What is meant by
specific acoustic impedanceof a medium [2] - What is meant by
attenuationof an ultrasound wave [1] - Describe the principles of CT scanning [5]
- Why an aluminium filter may be placed in the X-ray beam [3]
- Explain difference between X-ray images of bone and of muscle, referring to lightness of images [2]
- Two causes of lack of sharpness of an X-ray image [2]
- Describe the functions of the two B-fields in MRI [4]
- The function of the large uniform magnetic field in MRI [3]
- Explain the function of the small non-uniform magnetic field in MRI [3]
- Explain the principles of the generation of
ultrasound waves[4] - Explain the principles of the detection of
ultrasound waves[4] - Explain the principles of the use of
ultrasound waves[6] - Why ultrasound use high frequency [1]
- Why ultrasound used in medical diagnosis is emitted in pulses [2]
- Why little transmission of ultrasound waves from air into skin (specific acoustic impedance) [3]
- What is meant by
Telecommunication
What is meant by frequency modulation/amplitude modulation [2]
- frequency/amplitude of carrier wave varies
- … in synchrony with displacement of information signal.
Why FM costs more than AM [2]
- More complex circuitry
- More stations required (smaller ranges)
What is meant by noise [2]
- random signal
- that added to transmitted signal.
What is meant by attenuation of a signal [1]
- reduction in power of the signal.
What is meany by bandwidth of signal [1]
s18 42 Q5
- Range of frequencies of signal
Why regenerator amplifiers do not amplify the noise [2]
- For signal only the high and low are necessary.
- Variation between highs and lows caused by noise not required.
Why use optic fibres than wire pair [3]
s20 42 Q6 [3]
- Less attenuation
- Less noise
- Grater bandwidth
- Less cross-linking (greater security)
Why use infra-red than visible light in optic fibres [2]
- Less attenuation
- Fewer amplifiers
Frequency range of waves [5]
| Type | Wavelength | Range |
|---|---|---|
| space wave | less than 10 m | line of sight |
| sky wave | 10 m ~ 100 m | global |
| ground wave | more than 100 m | 1000 km |
What is meant by cross-talk / crosslinking [2]
s20 43 Q6 [2]
- Power is radiated.
- Signal picked up by adjacent wire.
Functions of the copper braid [2]
w19 43 Q5 [2]
- acts as ‘return’ for the signal.
- shields inner core from noise.
Draw a diagram for coaxial cable [2]
State three advantages of a coaxial cable compared with a wire pair [2]
- Less interference
- Less noise
- Greater bandwidth
- Less attenuation (sometimes this is not in the MS)
The principles of the geostationary satellite [4]
- Carrier wave transmitted from Earth to satellite.
- Satellite receives greatly attenuated signal.
- Signal amplified and transmitted back to Earth.
- Different frequencies prevent swamping of uplink signal.
The features of the geostationary orbit [2]
w18 42 Q5 [2]
m19 42 Q4 [2]
w19 43 Q1 [2]
- above the Equator.
- from west to east.
- circular.
- period is 24 hours.
Compare ionospheric reflection of radio than satellite communication [4]
- Ion layer varies in height so unreliable.
- Bandwidth too low so cannot carry all information needed.
Why use frequencies of gigahertz for satellite communication [1]
w18 42 Q5
- Minimal reflection by atmosphere
Why the uplink and downlink frequencies must be different [2]
w18 42 Q5
- Signal must be amplified before transmission back to Earth.
- Uplink signal would be swamped by downlink signal.
What is meant by an analogue signal [1]
- Signal has same variation as the data
What is meant by a digital signal [2]
- Can be regenerated
- Extra data can be added to check
Explain two advantages of the transmission of information in digital than analogue [4]
- Signal can be regenerated so that minimal noise.
- Extra data can be added so that signal can be checked for errors
Why base stations for mobile phone use high frequency [2]
- Short wavelength
- … so convenient length aerial.
How to improve the quality of the received analogue signal (ADC-DAC) [4]
s17 42 Q5 [2] (effects only)
- Increase the number of bits used for each sample, to make
step heightsmaller, and reproduced sound more accurate. - Increase frequency of sampling, to make
step width(step depth) smaller
Why neighbouring cells use different carrier frequencies (mobile phone) [1]
- No interference near boundaries.
Why each cell has a limited area (mobile phone) [1]
- For large area, signal strength would be too large and very damage health.
Why cellular exchange always operates for the phone [3]
- Mobile phone is sending out a signal.
- Computer continuously selects cell station
- … with strongest signal.
- Computer allocates frequency.
Explain the purpose of the switch in the mobile phone circuitry [1]
- Enables one aerial to be used for transmission and receipt of signals
Explain the purpose of the parallel-to-serial converter [2]
- All bits for one number arrive at one time.
- Bits are sent out one after another.
Medical Physics
What is meant by specific acoustic impedance of a medium [2]
w19 42 Q5
- Product of density and speed
- … of sound in the medium.
What is meant by attenuation of an ultrasound wave [1]
w19 42 Q5
- reduction in amplitude
- … as the wave pass through medium.
Describe the principles of CT scanning [5]
s18 42 Q11 [5] w19 42 Q7 [5]
- X-ray image taken of one slice.
- Many images taken from different angles.
- Computer produces 2D image of slice.
- This is repeated for many slices
- … to build up a 3D image.
Why an aluminium filter may be placed in the X-ray beam [3]
m20 42 Q11
- X-ray beam contains many wavelengths.
- Low energy X-rays absorbed by Aluminium filter
- … so not absorbed in the body.
- Low energy X-rays can cause harm but do not contribute to the image.
Explain difference between X-ray images of bone and of muscle, referring to lightness of images [2]
m20 42 Q11
Whiter regions mean greater absorption.
- Bone has higher
μso absorbs more. - Bone is lighter.
Two causes of lack of sharpness of an X-ray image [2]
m18 42 Q12 [2]
- Scattering of X-ray beam.
- Lack of collimation of beam.
- Anode area large.
- Photon energy low.
Describe the functions of the two B-fields in MRI [4]
- Strong uniform field
- … aligns nuclei.
- Non-uniform field
- … enables nuclei to be located.
The function of the large uniform magnetic field in MRI [3]
s19 42 Q9 [3]
w19 43 Q9 [2]
- Nuclei precess.
- Precession is about direction of magnetic field.
- frequency of precession depends on field strength.
Explain the function of the small non-uniform magnetic field in MRI [3]
w18 42 Q10 [3]
s19 42 Q9 [2]
w19 43 Q9 [2]
Always write them all.
- Enables nuclei to be located.
- Frequency of precession depends on magnetic field strength at the point.
- Unique field strength at each point.
- Non-uniform field may be varied to enable detection in different positions.
Explain the principles of the generation of ultrasound waves [4]
m17 42 Q4 [4]
w17 42 Q4 [5]
w20 43 Q4 [4]
- Alternating p.d. applied across quartz crystal, ([2])
- … causing it to vibrate.
- Resonance occurs when frequency of p.d. matches natural frequency of crystal.
- Natural frequency of crystal is in ultrasound range.
Explain the principles of the detection of ultrasound waves [4]
s20 42 Q5
- Pulses of ultrasound
- … incident on quartz crystal.
- Waves make quartz oscillate.
- Oscillations of crystal generates e.m.f.
Explain the principles of the use of ultrasound waves [6]
s17 42 Q4 [6]
m18 42 Q5 [6]
Bold - required, [4].
Italic - details, max [2].
- Pulses of ultrasound
- … produced by quartz crystal.
- Gel medium used to reduce reflection at skin.
- Ultrasound reflected from boundaries.
- Reflected wave detected by transmitter.
- Reflected wave processed and displayed.
- Intensity of reflected wave gives information about boundary.
- Time delay gives information about depth of boundary.
Why ultrasound use high frequency [1]
w17 42 Q4 [1]
- Smaller structures can be resolved.
Why ultrasound used in medical diagnosis is emitted in pulses [2]
m20 42 Q4
- Allows reflected signal to be distinguished from the emitted signal.
- Detection occurs in the time between emitted pulses.
- Reflected sound detected by same crystal.
- Cannot emit and detect at the same time.
Why little transmission of ultrasound waves from air into skin (specific acoustic impedance) [3]
s20 42 Q5
- Specific acoustic impedances of air and skin are very different.
- Intensity reflection coefficient depends on difference between acoustic impedance.
- Most ultrasound reflected so little transmission.