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PHTY2240 MSE > L15: Physics of Electromagnetism (Physics Module Lecture 5) > Flashcards

L15: Physics of Electromagnetism (Physics Module Lecture 5) Flashcards

1
Q

What is the important thing to understand about magnetism?

A

Comes in a pair (north and south)

It is impossible to find a monopole

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2
Q

How does MRI imaging look like in terms of the magnetic field?

A

1.5 telsa = huge magnetic fields

Can pass through body with minor interactions

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3
Q

How does magnetic therapy work?

A

Locate permanent magnets near painful area

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4
Q

There are no adverse effects for magnetic field strengths for ______ T

A

<2

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5
Q

What are the 2 significant effects with strong fields?

A
  1. Induced electric potential across blood vessels
    • As charged material gets through –> it bends
  2. Induced electric field in head -> sensory perceptions Transcranial magnetic stimulation = induce electric field in head = sensory perceptions
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6
Q

Strong magnetic fields can interfere with _____ equipment eg: pacemaker

A

electrical

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7
Q

What are the 3 interactions of magnetism and electricity?

A
  1. Every electric current creates a magnetic field
  2. An electric charge moving through a magnetic field experiences a force
  3. A changing magnetic field can create an electric
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8
Q

Every electric current creates a ____ field

A

magnetic

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9
Q

An electric charge moving through a magnetic field experiences a _____.

A

force

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10
Q

A changing magnetic field can create an ______

A

electric current

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11
Q

Changing electric and _____ fields support each other

A

magnetic

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12
Q

What are 2 characteristics of the electromagnetic wave?

A
  1. Transverse wave of oscillating electric & magnetic fields eg: “light”
  2. Transports energy
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13
Q

What do permanent magnets do?

A

Create a field

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14
Q

What is an oscillating field?

A

Oscillating field = along a line a photon (electric magnetic wave) will travel in a certain direction

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15
Q

What is the difference between electromagnetic wave and a photon? Give 2 examples?

A

Same thing = used interchangeable (only depending on how it is measured)

  • Electromagnetic wave: Light from projection (point source)
  • Photon: Light hit the hand (in front of projector)
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16
Q

What does velocity and energy look like in terms of electromagnetic waves and photons?

A
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17
Q

What is the relationship between energy and wavelength (what is the electromagnetic spectrum look like)?

A
18
Q

Higher frequency has _____ (longer/shorter) wavelengths

A

Low

19
Q

Lower frequency has _____ (longer/shorter) wavelengths

A

High

20
Q

What happens during ionisation?

A

Each photon does have enough energy to eject electron = proton gets absorbed = creates an ion

21
Q

A photon of ionising radiation has sufficient energy to remove______ from material if it is absorbed –> can affect biochemical reactions.

A

electron(s)

22
Q

How can microwave be used for therapeutic and biomedical imaging?

A

Deep heating of tissue (shortwave diathermy) (similar to ultrasound)

23
Q

How can infrared radiation be used for therapeutic and biomedical imaging?

A

superficial heating of tissue

24
Q

How can visible radiation be used for therapeutic and biomedical imaging?

A

visual inspection, photodynamic therapy (You can affect by the visible lights = biophysical effects= eg. laser)

25
Q

How can ultraviolet radiation be used for therapeutic and biomedical imaging?

A

sterilisation

26
Q

How can x-ray be used for therapeutic and biomedical imaging?

A

diagnostics

27
Q

How can gamma be used for therapeutic and biomedical imaging?

A

cancer treatment (PET scans)

28
Q

Which of the following factors can affect the impact of exposure to laser EM radiation? Why?

  1. Distance from source
  2. Duration of exposure
  3. Type of EM radiation (photon)
  4. Both 2 and 3
  5. All 1 and 2 and 3
A
  1. Both 2 and 3

Doesn’t matter how far –> Can propagate through air well

Only placed directly on skin due to safety

29
Q

Laser is the _____form of electromagnetic radiation (as out picks out a specific part of ____) ****

A

purest

30
Q

Why is angle of the laser light source very important? How does it makes a difference if the laser is at an angle?

A

Larger area = less intensity

31
Q

Consider a laser beam incident on a curved body part. Compare the intensities at the locations indicated.

Why?

  1. They all experience the same intensity
  2. A experiences the highest intensity
  3. C experiences the highest intensity
A
  1. A experiences the highest intensity

Not coming in on an angle

Eg. Brisbane in winter is at C = getting less sun (intensity) Eg. Brisbane in summer is at A = getting more sun (intensity)

32
Q

What is the total energy of laser beam?

A

photons x energy of each

33
Q

What is surface intensity?

A

amount of energy delivered per unit time per unit area

34
Q

What can happen when EM radiation interacts with matter?

A

Through a region of uniform matter, each light ray travels in

  • a straight line
  • at a constant speed
35
Q

When light strikes a different substance/interface, what are 4 things it can be?

A
  1. Reflected
  2. Refracted
  3. Scattered
  4. Absorbed
36
Q

Absorption causes intensity to decrease ______ with distance travelled through medium. Energy is progressively absorbed

A

exponentially

37
Q

Scattering depends on _____. High-frequency EM radiation scatters ____ (more/less). Therefore, you use _____ (high/low)-frequency EM radiation to penetrate deeper

A

frequency; more; low

38
Q

How thick is the epidermis?

A

Couple mms

39
Q

How thick is the dermis?

A

• Thicker than epidermis Has more capillaries, arteries

40
Q

What is the sweet spot for laser? What does it look like?

A

(3mm) Where the laser gets through very easily

PHTY2240 MSE (17 decks)

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