This physics course for medical students covers basic physics concepts with medical applications. It presents physics simply and covers the most important applications to help students understand and apply physics concepts. Topics include measurements, units, light, lasers, electromagnetic waves, sound, fluid mechanics, temperature, electricity, nuclear physics, and nanotechnology. Light exhibits both wave and particle properties, behaving as a wave in some situations and particles called photons in others. Reflection and refraction follow the laws of reflection and refraction at boundaries between mediums. Total internal reflection inside optical fibers allows them to transmit light along their lengths.

1. AlMughtaribeen University
College of Medicine
Physics
Course Descriptions & Course Outlines :
This Course cover a range of basic physics concepts and are useful
as a supplement to an introductory physics course with medical
applications. The course present the concepts of physics simply
and covers the most important applications of physics to help
medical students to understand and apply these concepts.
Physics course include :  Measurements , Measurements Errors
Units ,  Units conversation ,  Significant digits (2 Lectures ) .
Light ,Laser and its applications (4 Lectures) , Sound
,Electromagnetic waves ( 2 lectures ) ,Fluid Mechanics in medicine
(2 lectures ), Temperature &heat ( 1Lecture ) , Electric charge &
current (1 Lecture) , Nuclear physics & radio activity (2 Lectures) ,
concept of Nanotechnology (1 Lectures ) .
Mr.Gazy Khatmi Email _ gazy@mu.edu.sd
AlMughtaribeen University - College of Medicine
1January 19, 2016

2. Light
2January 19, 2016

3. Introduction :
Why Light ??!
 These days light is frequently used for all sorts of therapies
and medical applications, from cancer diagnosis and treatment
to monitoring of oxygen in the blood.
 Biophotonics is a relatively new scientific discipline which is
developing applications for light and lasers in the life sciences -
for clinical diagnostics and therapy, and even semi-automated
diagnostic systems for doctors and nurses.
 Biophotonics also deals with the prevention of diseases; light
can be used for precision monitoring of our environment as
well as assessing the quality of food.
3January 19, 2016

4. The Nature of Light
Before the beginning of the nineteenth century, light was considered to be a stream of
particles.
The particles were either emitted by the object being viewed or emanated.
Newton was the chief architect of the particle theory of light.
Huygens argued that light might be some sort of a wave motion.
Thomas Young (in 1801) provided the first clear demonstration of the wave nature of
light.
 He showed that light rays interfere with each other.
 Such behavior could not be explained by particles
4January 19, 2016

5. Confirmation of Wave Nature
During the nineteenth century, other developments led to the general acceptance of
the wave theory of light.
Thomas Young provided evidence that light rays interfere with one another
according to the principle of superposition.
 This behavior could not be explained by a particle theory.
Maxwell asserted that light was a form of high-frequency electromagnetic wave.
Hertz confirmed Maxwell’s predictions.
5January 19, 2016

6. Particle Nature
Some experiments could not be explained by the wave model of light.
The photoelectric effect was a major phenomenon not explained by waves.
 When light strikes a metal surface, electrons are sometimes ejected from
the surface.
 The kinetic energy of the ejected electron is independent of the frequency of
the light.
Einstein (in 1905) proposed an explanation of the photoelectric effect that used the
idea of quantization.
 The quantization model assumes that the energy of a light wave is present
in particles called photons.
E = hƒ
 h is Planck’s Constant and = 6.63 x 10-34
J.
s
6January 19, 2016

7. dual nature:
wave vs.particle
Wave: continuously
changing force fields
 energy travels as sine
WAVE
 macroscopic level
Particle: photon or quanta
 small packet of energy
acting as a PARTICLE
 microscopic level
7
Dual Nature of EM Radiation
January 19, 2016

8. Dual Nature of Light
In view of these developments, light must be regarded as having a dual
nature.
Light exhibits the characteristics of a wave in some situations and the
characteristics of a particle in other situations.
This chapter investigates the wave nature of light
8January 19, 2016

9. Ray Approximation
The rays are straight
lines perpendicular to
the wave fronts.
With the ray
approximation, we
assume that a wave
moving through a
medium travels in a
straight line in the
direction of its rays.
Section 35.3
9January 19, 2016

10. Ray Approximation, cont.
If a wave meets a barrier, with
λ<<d, the wave emerging from the
opening continues to move in a
straight line.
 d is the diameter of the
opening.
 There may be some small
edge effects.
This approximation is good for the
study of mirrors, lenses, prisms, etc.
Other effects occur for openings of
other sizes.
 See fig. 35.4 b and c
Section 35.3
10January 19, 2016

11. 11January 19, 2016

12. Reflection of Light
A ray of light, the incident ray, travels in a medium.
When it encounters a boundary with a second medium,
part of the incident ray is reflected back into the first
medium.
 This means it is directed backward into the first
medium.
For light waves traveling in three-dimensional space, the
reflected light can be in directions different from the
direction of the incident rays.
Section 35.4
12January 19, 2016

13. Specular Reflection
Specular reflection is reflection
from a smooth surface.
The reflected rays are parallel
to each other.
All reflection in this text is
assumed to be specular.
Section 35.4
13January 19, 2016

14. Diffuse Reflection
Diffuse reflection is
reflection from a rough
surface.
The reflected rays travel in
a variety of directions.
A surface behaves as a
smooth surface as long as the
surface variations are much
smaller than the wavelength
of the light.
Section 35.4
14January 19, 2016

15. Law of Reflection
The normal is a line
perpendicular to the surface.
 It is at the point where
the incident ray strikes
the surface.
The incident ray makes an
angle of θ1 with the normal.
The reflected ray makes an
angle of θ1’with the normal.
Section 35.4
15January 19, 2016

16. Law of Reflection, cont.
The angle of reflection is equal to
the angle of incidence.
θ1’= θ1
This relationship is called the Law of Reflection.
The incident ray, the reflected ray and the normal are all in
the same plane.
Section 35.4
16January 19, 2016

17. Refraction of Light
When a ray of light traveling through a transparent medium
encounters a boundary leading into another transparent medium,
part of the energy is reflected and part enters the second medium.
The ray that enters the second medium changes its direction of
propagation at the boundary.
 This bending of the ray is called refraction.
Section 35.5
17January 19, 2016

18. Refraction, cont.
The incident ray, the reflected ray, the refracted ray, and the
normal all lie on the same plane.
The angle of refraction depends upon the material and the angle
of incidence.
 v1 is the speed of the light in the first medium and v2 is its
speed in the second.
2 2
1 1
sin
sin
θ v
θ v
=
Section 35.5
18January 19, 2016

19. Refraction of Light, final
The path of the light
through the refracting surface
is reversible.
 For example, a ray
travels from A to B.
 If the ray originated at
B, it would follow the
line AB to reach point
A.
Section 35.5
19January 19, 2016

20. Refraction Details, 1
Light may refract into a
material where its speed is
lower.
The angle of refraction is
less than the angle of
incidence.
 The ray bends toward
the normal.
Section 35.5
20January 19, 2016

21. Refraction Details, 2
Light may refract into a
material where its speed is
higher.
The angle of refraction is
greater than the angle of
incidence.
 The ray bends away from
the normal.
Section 35.5
21January 19, 2016

22. Light in a Medium
The light enters from the left.
The light may encounter an
electron.
The electron may absorb the light,
oscillate, and reradiate the light.
The absorption and radiation cause
the average speed of the light
moving through the material to
decrease.
Section 35.5
22January 19, 2016

23. The Index of Refraction
The speed of light in any material is
less than its speed in vacuum.
The index of refraction, n, of a
medium can be defined as
speed of light in a vacuum c
n
speed of light in a medium v
≡ ≡
Section 35.5
January 19, 2016 23

24. Frequency Between Media
As light travels from one
medium to another, its frequency
does not change.
Both the wave speed and the
wavelength do change.
The wavefronts do not pile up,
nor are they created or
destroyed at the boundary, so ƒ
must stay the same.
Section 35.5
January 19, 2016 24

25. Index of Refraction Extended
The frequency stays the same as the wave travels from one
medium to the other.
v = ƒλ
ƒ1 = ƒ2 but v1 ≠ v2 so λ1 ≠ λ2
The ratio of the indices of refraction of the two media can be expressed as
various ratios.
The index of refraction is inversely proportional to the wave speed.
As the wave speed decreases, the index of refraction increases.
The higher the index of refraction, the more it slows downs the light
wave speed.
Section 35.5
January 19, 2016 25

26. Fiber Optics
26January 19, 2016

27. Total Internal Reflection
A phenomenon called total internal
reflection can occur when light is
directed from a medium having a given
index of refraction toward one having a
lower index of refraction.
Section 35.8
January 19, 2016 27

28. Critical Angle
There is a particular angle of
incidence that will result in an angle
of refraction of 90°.
This angle of incidence is called
the critical angle, θC.
For angles of incidence greater than
the critical angle, the beam is
entirely reflected at the boundary.
This ray obeys the law of
reflection at the boundary.
Total internal reflection occurs only
when light is directed from a medium
of a given index of refraction toward
a medium of lower index of
refraction.
2
1 2
1
sin (for )C
n
θ n n
n
= >
Section 35.8
January 19, 2016 28

29. Acceptance angle
 Having considered the propagation of light in an optical
fiber through total internal reflection at the core–
cladding interface, it is useful to enlarge upon the
geometric optics approach with reference to light rays
entering the fiber. Since only rays with a sufficiently
shallow grazing angle (i.e. with an angle to the normal
greater thanφc) at the core–cladding interface are
transmitted by total internal reflection, it is clear that not
all rays entering the fiber core will continue to be
propagated down its length
29January 19, 2016

30. 30January 19, 2016

31. Numerical aperture
31January 19, 2016

32. Cont,
32
Equation above, apart from relating the acceptance angle to the refractive
indices, serves as the basis for the definition of the important optical fiber
parameter, the numerical aperture (NA). Hence the NA is defined as
January 19, 2016

33. Example 1

A silica optical fiber with a core diameter large enough to be
considered by ray theory analysis has a core refractive index of
1.50 and a cladding refractive index of 1.47.
Determine: (a) the critical angle at the core–cladding interface;
(b) the NA for the fiber; (c) the acceptance angle in air for the
fiber.
33January 19, 2016

34. 34January 19, 2016

35. Attenuation
 Attenuation is defined as the ratio of optical output power to the
input power in the fiber of length L.
α= 10log10 Pi/Po [in db/km]
where, Pi= Input Power
Po= Output Power, α is attenuation constant
The various losses in the cable are due to
 Absorption
 Scattering
 Dispersion
 Bending
January 19, 2016 35