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physics a2 > Medical - Ear, eye and heart > Flashcards

Medical - Ear, eye and heart Flashcards

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1
Q

Explain what the pinna does

3 points

A

The pinna channels longitudinal waves into the auditory canal.
Conc in small A = increase in intensity.
Variations in air pressure causes eardrum to vibrate

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2
Q

What is the function of the:

Eardrum
Ossicle lever system
Oval window
Cochlea

A

Vibrates mechanically and transfers energy to the inner ear

Transmits vibrations from the eardrum to the oval window

Transmits vibrations into the fluid in the inner ear

Converts pressure waves in the fluid into electrical signals which are sent to the brain

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3
Q

Explain how components of the ear act to amplify pressure changes

(3 marks)

A

Ossicles lever system produce an increase in force
Area of the oval window is much smaller than the area of the eardrum
P = F/A so pressure greatly increases

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4
Q

How are vibrations of a sound wave transmitted to the inner ear from the outer ear?

(3 marks) - 4 possible marks

A

Longitudinal/pressure waves in the auditory canal
Forces eardrum into mechanical vibrations
Vibrations passed through the middle ear by lever system to the oval window
Sets up pressure waves in cochlea

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5
Q

Define intensity

What is the formula for intensity?

Unit?

A

The energy per second per unit area incident normally on a surface

I = P/A

Wm-2

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6
Q

What is the relation between intensity and amplitude?

A

Intensity is proportional to amplitude squared

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7
Q

Define threshold of hearing

A

The minimum intensity level that can be heard by a normal ear at a frequency of 1kHz

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8
Q

How can you obtain an equal loudness curve?

4 steps

A
  1. Using signal generator, generate a control frequency of 1000Hz at a particular intensity
  2. Using a second signal generator, set a different frequency and adjust the intensity level until the signal generators produce the same loudness. Make note of this f and I
  3. Repeat this step for several frequencies and plot curve
  4. Adjust the intensity of the control signal generator and repeat experiment
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9
Q

What causes hearing loss? What are the effects of these causes?

(2 marks)

A

Aging - hearing loss increases as frequency increases

Excessive noise - hearing loss increases up to 4kHz, then decreases after this frequency

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10
Q

Describe an electrocardiogram trace whilst staring each relevant time interval

A
  1. 2s - aorta contract
  2. 4s - ventricles contract and aorta relax
  3. 6 to 0.8s - ventricles relax
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11
Q

How is an ECG trace obtained

A

Electrode are placed on a patients chest or limbs and a change in potential difference is measured

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12
Q

What precautions are taken when taking an ECG trace?

A

Sandpaper skin - remove dead skin and hair cells to increase conductivity and decrease contact resistance
Securely attach electrodes - prevents voltage spikes by the electrostatic effect of motion
Conductive gel between skin and electrode - reduce contact resistance

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13
Q

What are the design features of the electrodes of an ECG

A

Large input impedance amplifier - reduces current between patient and machine and causes signal gain
High gain amplifier - amplifies signal, required because voltage is very small
Low noise amplifier - doesn’t pick up unwanted signals

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14
Q

What are the characteristics of the:

Cornea
Lens
Retina
Optic nerve

A

High refractive index and convex shape, focuses on objects

Muscles contract - lens fattens. Muscles relax - lens thins. These change the focal length

Contains light sensitive rods and cones and a very sensitive yellow spot

Carries signals from the rods to the brain

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15
Q

What are rods and cones?

How does it carry out its function?

A

Photoreceptors that detect light and convert to it an electrical signal

They bleach when light hits them due to a chemical pigment
This stimulates the cell, causing them to send signals to the brain via optic nerve

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16
Q

What do cones detect?

A

Colour

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17
Q

What is required for two objects to be distinguished between each other?

Where is spatial resolution the greatest? Why?

A

The light from the object must be hitting rods or cones that are attached to separate optic nerves

At the yellow spot. It contains the most densely packed cones and rods

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18
Q

Define principal focus

A

The point on the principal axis through which rays which were parallel to the principal axis pass after refraction by the lens

19
Q

Define Focal length

What is it’s unit?

A

The distance between the lens and the focal plane

Diopters, D

20
Q

Define power

A

The reciprocal of the focal length measured in meters

21
Q

What does u and v stand for in the equation for in the lens equation?

A

u - the distance between the object and the lens

v - the distance between the lens and the image

22
Q

What are the properties of the image produced from a diverging lens?

A

Virtual
Upright
Smaller than object

23
Q

When does short sightedness occur?

3 points

A

When the:
Cornea and lens are too powerful
Eyeball too long
Image focus is in front of retina

24
Q

How do you correct short sightedness?

A

Use a diverging lens with negative power with principal focus at the faulty far point and negative focal length to the far point

25
Q

When does long sightedness occur?

3 points

A

When the:
Cornea and lens are too weak
Eyeball too short
Image focus behind retina

26
Q

How do you correct long sightedness?

A

Use a converging lens with positive power with the virtual image produced at uncorrected near point of object in front of near point

27
Q

What is the format of subscription of astigmatism?

A

Power and axis of cylindrical lens

28
Q

Outline how the piezoelectric effect produces waves in an ultrasound transducer

(5 points)

A
  1. Two faces of a thin slice of crystal is used as electrodes
  2. Electrodes are connected to a high frequency emf source
  3. Alternating emf induces an alternating electric field across the piezoelectric crystals between the electrodes
  4. The crystals expand and contract at the same frequency as applied emf
  5. Vibrations of the crystals produce ultrasound pressure waves
29
Q

How is a signal received by the transducer?

A

Waves are reflected at a boundary and are received by transducer, causing crystals to vibrate
Vibration of crystals induce an emf

30
Q

Define acoustic impedance

A

The amount of reflection ultrasound waves experience at a boundary

31
Q

What is attenuation?

What is done to reduce it? Why? What is the disadvantage of this method?

A

The scattering and absorption of ultra sound waves as they travel through a material

Low frequency impulses are used for deeper tissue. Intensity of reflected waves decrease as depth increases due to attenuation and low freq waves are less attenuated
Poorer resolution

32
Q

How and why is a coupling media used in ultrasound?

A

It is used to displace air between the probe and tissue. Air and tissue have a very large difference in impedance which would cause all of the waves to be reflected before entering the tissue
Gell impedance = tissue impedance

33
Q

How is an A scan produced?

A

Short pulses are transmitted and received by probe and signal sent to oscilloscope

34
Q

What do the spacing of the pulses in an A scan show you? Wat can be found using this knowledge?

A

Echoes that are reflected back to transducer appear as voltage peaks on the graph
The spacing gives time delay between transmitted pulse and echo
Distance = 1/2 speed x time

35
Q

How is a B scan produced?

A

Amplitude of pulses displayed as bright spots, forming an image

36
Q

Advantages of ultrasound

3 points

A

Produces high quality imaging of soft tissue
Cheap, portable and quick
No ionizing radiation so no known side effects

37
Q

Disadvantages of ultrasound

4 points

A

Doesn’t penetrate bone
Doesn’t give information on large masses
Cannot pass through air spaces in body
Poor resolution

38
Q

Describe a coherent optical fiber bundle

A

The relative positions of the fibers remain the same at the start and end of the fiber bundle.
They transmit image and light
Image can be magnified by gradually increasing the diameter of the fibers

39
Q

Describe a non-coherent optical fiber

A

The positions of the fibers change.

Cheaper to make but can only transmit light

40
Q

What is an endoscope

What causes a loss of light and image? Why?

A

Bundles of coherent and incoherent optical fibers used for body examination

Large curvature of the fiber because the angle of incidence decreases and may decrease below the critical angle, resulting in no total internal reflection

41
Q

What channels may an endoscope contain?

A

Water channel - used to clean objective lens

CO2 channel - used to make room in body

42
Q

Why is keyhole surgery advantageous?

A

Reduces risk of infection

Reduces recovery time and hence price

43
Q

Describe how the frequency and amplitude of the vibrations change as a wave is transmitted through the ear to the fluid in the inner ear

A

Frequency is the same

Amplitude is reduced

physics a2 (11 decks)

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