L15: Physics of Electromagnetism (Physics Module Lecture 5) Flashcards
What is the important thing to understand about magnetism?
Comes in a pair (north and south)
It is impossible to find a monopole
How does MRI imaging look like in terms of the magnetic field?
1.5 telsa = huge magnetic fields
Can pass through body with minor interactions
How does magnetic therapy work?
Locate permanent magnets near painful area
There are no adverse effects for magnetic field strengths for ______ T
<2
What are the 2 significant effects with strong fields?
- Induced electric potential across blood vessels
- As charged material gets through –> it bends
- Induced electric field in head -> sensory perceptions Transcranial magnetic stimulation = induce electric field in head = sensory perceptions
Strong magnetic fields can interfere with _____ equipment eg: pacemaker
electrical
What are the 3 interactions of magnetism and electricity?
- Every electric current creates a magnetic field
- An electric charge moving through a magnetic field experiences a force
- A changing magnetic field can create an electric
Every electric current creates a ____ field
magnetic
An electric charge moving through a magnetic field experiences a _____.
force
A changing magnetic field can create an ______
electric current
Changing electric and _____ fields support each other
magnetic
What are 2 characteristics of the electromagnetic wave?
- Transverse wave of oscillating electric & magnetic fields eg: “light”
- Transports energy
What do permanent magnets do?
Create a field
What is an oscillating field?
Oscillating field = along a line a photon (electric magnetic wave) will travel in a certain direction
What is the difference between electromagnetic wave and a photon? Give 2 examples?
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)
What does velocity and energy look like in terms of electromagnetic waves and photons?
What is the relationship between energy and wavelength (what is the electromagnetic spectrum look like)?
Higher frequency has _____ (longer/shorter) wavelengths
Low
Lower frequency has _____ (longer/shorter) wavelengths
High
What happens during ionisation?
Each photon does have enough energy to eject electron = proton gets absorbed = creates an ion
A photon of ionising radiation has sufficient energy to remove______ from material if it is absorbed –> can affect biochemical reactions.
electron(s)
How can microwave be used for therapeutic and biomedical imaging?
Deep heating of tissue (shortwave diathermy) (similar to ultrasound)
How can infrared radiation be used for therapeutic and biomedical imaging?
superficial heating of tissue
How can visible radiation be used for therapeutic and biomedical imaging?
visual inspection, photodynamic therapy (You can affect by the visible lights = biophysical effects= eg. laser)
How can ultraviolet radiation be used for therapeutic and biomedical imaging?
sterilisation
How can x-ray be used for therapeutic and biomedical imaging?
diagnostics
How can gamma be used for therapeutic and biomedical imaging?
cancer treatment (PET scans)
Which of the following factors can affect the impact of exposure to laser EM radiation? Why?
- Distance from source
- Duration of exposure
- Type of EM radiation (photon)
- Both 2 and 3
- All 1 and 2 and 3
- Both 2 and 3
Doesn’t matter how far –> Can propagate through air well
Only placed directly on skin due to safety
Laser is the _____form of electromagnetic radiation (as out picks out a specific part of ____) ****
purest
Why is angle of the laser light source very important? How does it makes a difference if the laser is at an angle?
Larger area = less intensity
Consider a laser beam incident on a curved body part. Compare the intensities at the locations indicated.
Why?
- They all experience the same intensity
- A experiences the highest intensity
- C experiences the highest intensity
- 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)
What is the total energy of laser beam?
photons x energy of each
What is surface intensity?
amount of energy delivered per unit time per unit area
What can happen when EM radiation interacts with matter?
Through a region of uniform matter, each light ray travels in
- a straight line
- at a constant speed
When light strikes a different substance/interface, what are 4 things it can be?
- Reflected
- Refracted
- Scattered
- Absorbed
Absorption causes intensity to decrease ______ with distance travelled through medium. Energy is progressively absorbed
exponentially
Scattering depends on _____. High-frequency EM radiation scatters ____ (more/less). Therefore, you use _____ (high/low)-frequency EM radiation to penetrate deeper
frequency; more; low
How thick is the epidermis?
Couple mms
How thick is the dermis?
• Thicker than epidermis Has more capillaries, arteries
What is the sweet spot for laser? What does it look like?
(3mm) Where the laser gets through very easily
