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Further Additional Physics > Topic 2 - X-rays and ECGs > Flashcards

Topic 2 - X-rays and ECGs Flashcards

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1
Q

Explain the process of thermionic emission and how this can lead to the production of X-rays.

A
  • Filament (cathode, -vely charged electrode); heated so electrons have more energy
  • With enough energy, ‘boil off’ (escape). Thermionic emission.
  • Electrons accelerated towards anode (+ve electrode) by potential difference (voltage) between cathode and anode
  • When electrons collide with metal target (anode), some kinetic energy converted to X-rays
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2
Q

In thermionic emission, why is the filament heated?

A

Gives more energy to its electrons

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3
Q

Why is thermionic emission done in a vacuum?

A

Prevent electrons colliding with air particles (knock them off target + decrease energy)

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4
Q

Why is a lead casing put around the tube in which thermionic emission takes place?

A

Absorb some of the X-rays so only aimed at one small area, e.g. in hospitals aimed at something specific like an arm

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5
Q

What is energy measured in?

A

joules, J

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6
Q

What is charge measured in?

A

coulombs, C

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7
Q

What is potential difference measured in?

A

Volts, V

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8
Q

What is the formula for the kinetic energy gained by each electron as it accelerates in thermionic emission?

A

kinetic energy = electronic charge (e) x accelerating potential difference (V)

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9
Q

What is current measured in?

A

amperes, A

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10
Q

What is the formula for current of the beam of electrons in thermionic emission?

A

Current (I) = number of particles per second (N) x charge on each particle (q)

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11
Q

What does the symbol e represent?

A

electrical charge, 1.6x10^-19

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12
Q

Why are X-rays potentially dangerous to our body?

A
  • Very high frequency so high energy

- Enough energy to ionise molecules in living cells (removing electrons from atoms so they’re +ve charged ions)

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13
Q

What effect can the ionisation from X-rays have on cells?

A

Damaged or destroyed, leading to tissue damage or cancer

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14
Q

What is the relationship between intensity and distance from the source?

A
  • Inverse square relationship

- e.g. if you move twice as far from source, radiation spread over 4x the area (1/2^2 = 1/4)

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15
Q

What kind of materials are used in hospitals to reduce people’s exposure to X-rays?

A

Lead and concrete

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16
Q

What factors affect how much X-ray radiation a material absorbs?

A
  • Density, more dense = more radiation absorbed

- Thickness of material, thicker = more absorbed

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17
Q

What type of electromagnetic wave is used in a fluoroscope?

A

X-rays

18
Q

How does fluoroscopy work?

A
  • Patient placed between X-ray source + fluorescent screen
  • Different amount of X-rays absorbed as pass through body
  • Intensity of rays vary on what they pass through
  • X-rays hit a fluorescent screen which absorbs them + fluoresces (gives off light) showing live image on screen by rays’ intensity (bright = more intense)
  • Modern fluoroscopy: generally involves image intensifier, increaser brightness of image so lower dose can be given
  • Attached to PC so image can be recorded
19
Q

What is fluoroscopy used for?

A
  • Diagnose problems in the way organs are functioning (e.g. movement through gastrointestinal tract or blood flow)
  • Can easily pass through soft tissue, patient given ‘contrast medium’ (injection/ingestion). Improves contrast of image seen by enhancing soft tissue so more visible
20
Q

What does CAT scan stand for?

A

computerised axial tomography scan

21
Q

What do CAT scans produce?

A

2D slices through the body

22
Q

How does CAT scanning work?

A
  • X-ray rotates around body + picked up by thousands of detectors
  • Computer works out how many X-rays absorbed + produce high quality image (especially useful to diagnose less obvious problems)
  • Can make 3D image by stacking individual slices
  • Often look for tumours/cancer
23
Q

What are the advantages of using X-rays for imaging and treatment?

A
  • Non invasive as no incisions or surgery
  • Generally quite quick
  • Usually higher quality images
  • Hospitals try to limit exposure to minimise risk
24
Q

What are the risks of using X-rays for imaging and treatment?

A
  • Other safer methods e.g. ultrasound (although usually lower quality image produces)
  • Ionising; cell mutation + cancer
25
Q

What type of cells in the body produce a potential difference (voltage) and how?

A
  • Muscle cells
  • Between inside of muscle cell and outside
  • Potential difference across cell membrane of muscle cell at rest is called resting potential
26
Q

What happens to the potential difference of a muscle cell when stimulated by an electrical signal?

A
  • The potential difference changes from -70mV to about +40mV.
  • This increased potential called action potential.
  • Action potential passes down length of the cell, making the muscle cell contract
27
Q

What do electrocardiographs measure?

A

The action potentials of the heart

28
Q

What is the heart made up of?

A
  • Muscle

- Split into 4 chambers (atria at top + ventricles at bottom)

29
Q

How does a heart beat occur (using action potential)?

A
  • Action potential passes through atria making them contract
  • Fraction of second later: another action potential passes through ventricles making them contract
  • Once action potential passed, muscles relax
  • Action potentials produce weak electrical signals on skin
30
Q

How does an electrocardiograph work?

A
  • Records action potentials of heart using electrodes stuck on chest, arms + legs
  • Results displayed on screen/printed as graph called electrocardiogram (ECG)
  • Used to look at action of the heart
31
Q

How would you work out heart rate from an ECG?

A

frequency (hertz) = 1 / time period (seconds)

Multiplying by 60 turns this to heart rate in beats per minute

32
Q

What is a pacemaker?

A

A device used to regulate heart beat

33
Q

What is an example of a natural pacemaker and how does it work?

A

In the heart - groups of cells in wall of right atrium that produce electrical signals that pule about 70 times a minute. Signals spread over the atria + make them contract by action potential. Signals pass to ventricles which contract too.

34
Q

What does the heart’s natural pacemaker control and what happens when this doesn’t work as well?

A
  • Heart rate
  • May not be fast enough
  • Irregular pulses
  • Other problems with electrical signals being sent
35
Q

What happens when the heart’s natural pacemaker when it cannot do its job properly and how does this help?

A
  • Artificial pacemaker fitted
  • Keeps heart beating steadily using small electric impulses to stimulate heart to beat
  • Small electric impulses sent via electrodes (thin wires attached to heart)
36
Q

How is a pacemaker fitted?

A
  • Minor surgery + only small incision to insdert it

- Powered by batteries so need replacing when battery loses power

37
Q

What are some features of modern pacemakers?

A
  • Can be programmed externally (settings can be changed without surgery again)
  • Monitor breathing/temperature, use this to match heart rate to activity being done
38
Q

What is the role of haemoglobin in the body?

A
  • Carries oxygen from lungs to cells around body
  • Pigment which makes blood red
  • Changes colour depending on oxygen content: lots of oxygen = bright red (oxyhaemoglobin), without oxygen = purply (reduced haemoglobin)
39
Q

How does a pulse oximeter work?

A
  • Has a transmitter, emitting 2 beams of red light. Has photo detector to measure it
  • Placed on either side of thing part of body e.g. finger/ear lobe
  • Beams of light pass through tissue. Some absorbed by blood, reducing light detected by detector
  • Amount of light absorption depends on blood colour, which depends on oxyhaemoglobin content
  • Arteries of healthy people: at least 95% oxyhaemoglobin + no more than 5% reduced haemoglobin
  • Reflection pulse oximetry uses similar technique; reflects light off red blood cells instead of shining light through part of body
40
Q

What is meant by the term ‘bradycardia’?

A

An abnormally slow heart rate

41
Q

What is meant by the term ‘tachycardia’?

A

An abnormally rapid heart rate

Further Additional Physics (5 decks)

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