L15: Physics of Electromagnetism (Physics Module Lecture 5)

Question 1

What is the important thing to understand about magnetism?

Answer 1

Comes in a pair (north and south)

It is impossible to find a monopole

Question 2

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

Answer 2

1.5 telsa = huge magnetic fields

Can pass through body with minor interactions

Question 3

How does magnetic therapy work?

Answer 3

Locate permanent magnets near painful area

Question 4

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

Answer 4

<2

Question 5

What are the 2 significant effects with strong fields?

Answer 5

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

Question 6

Strong magnetic fields can interfere with _____ equipment eg: pacemaker

Answer 6

electrical

Question 7

What are the 3 interactions of magnetism and electricity?

Answer 7

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

Question 8

Every electric current creates a ____ field

Answer 8

magnetic

Question 9

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

Answer 9

force

Question 10

A changing magnetic field can create an ______

Answer 10

electric current

Question 11

Changing electric and _____ fields support each other

Answer 11

magnetic

Question 12

What are 2 characteristics of the electromagnetic wave?

Answer 12

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

Question 13

What do permanent magnets do?

Answer 13

Create a field

Question 14

What is an oscillating field?

Answer 14

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

Question 15

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

Answer 15

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)

Question 16

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

Answer 16

Question 17

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

Answer 17

Question 18

Higher frequency has _____ (longer/shorter) wavelengths

Answer 18

Low

Question 19

Lower frequency has _____ (longer/shorter) wavelengths

Answer 19

High

Question 20

What happens during ionisation?

Answer 20

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

Question 21

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

Answer 21

electron(s)

Question 22

How can microwave be used for therapeutic and biomedical imaging?

Answer 22

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

Question 23

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

Answer 23

superficial heating of tissue

Question 24

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

Answer 24

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

Question 25

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

Answer 25

sterilisation

Question 26

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

Answer 26

diagnostics

Question 27

How can gamma be used for therapeutic and biomedical imaging?

Answer 27

cancer treatment (PET scans)

Question 28

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

Answer 28

4. Both 2 and 3 Doesn’t matter how far --\> Can propagate through air well Only placed directly on skin due to safety

Question 29

Laser is the \_\_\_\_\_form of electromagnetic radiation (as out picks out a specific part of \_\_\_\_) \*\*\*\*

Answer 29

purest

Question 30

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

Answer 30

Larger area = less intensity

Question 31

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

Answer 31

2. 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)

Question 32

What is the total energy of laser beam?

Answer 32

photons x energy of each

Question 33

What is surface intensity?

Answer 33

amount of energy delivered per unit time per unit area

Question 34

What can happen when EM radiation interacts with matter?

Answer 34

Through a region of uniform matter, each light ray travels in * a straight line * at a constant speed

Question 35

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

Answer 35

1. Reflected 2. Refracted 3. Scattered 4. Absorbed

Question 36

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

Answer 36

exponentially

Question 37

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

Answer 37

frequency; more; low

Question 38

How thick is the epidermis?

Answer 38

Couple mms

Question 39

How thick is the dermis?

Answer 39

• Thicker than epidermis Has more capillaries, arteries

Question 40

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

Answer 40

(3mm) Where the laser gets through very easily