# Chapter 13 The Characteristics of light - PowerPoint PPT Presentation

PPT – Chapter 13 The Characteristics of light PowerPoint presentation | free to download - id: 698726-M2MzM

The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
Title:

## Chapter 13 The Characteristics of light

Description:

### Chapter 13 The Characteristics of light * * * * * * * * * * * Objectives Identify the components of the electromagnetic spectrum. Calculate the frequency or ... – PowerPoint PPT presentation

Number of Views:4
Avg rating:3.0/5.0
Slides: 26
Provided by: Marlenea5
Category:
Tags:
Transcript and Presenter's Notes

Title: Chapter 13 The Characteristics of light

1
Chapter 13 The Characteristics of light
2
Objectives
• Identify the components of the electromagnetic
spectrum.
• Calculate the frequency or wavelength of
• Recognize that light has a finite speed .
• Describe how the brightness of a light source is
affected by distance.

3
Chapter 13 Vocabulary
• Electromagnetic waves a wave that consists of
oscillating electric and magnetic fields, which
radiate outward from the source at the speed of
light.
• Reflection the change in direction of an
electromagnetic wave at a surface that causes it
to move away from the surface.
• Angle of incidence the angle between a ray that
strikes a surface and the line perpendicular to
that surface at the point of contact.
• Angle of reflection the angle formed by the
line perpendicular to a surface and the direction
in which a reflected ray moves.
• Virtual image an image that forms at a point
from which light rays appear to come but do not
actually come.
• Concave spherical mirror a mirror whose
reflecting surface is a segment of the inside of
a sphere.
• Real image an image formed when rays of light
actually pass through a point on the image.
• Convex spherical mirror a mirror whose
reflecting surface is an outward-curved segment
of a sphere.
• Linear polarization the alignment of EM waves
in such a way that the vibrations of electric
fields in each of the waves are parallel to each
other.

4
Electromagnetic Waves
• Some light cannot be seen by the human eye.
• This is because light is measured in a variety of
• These forms are examples of electromagnetic
waves.
• They vary depending on frequency and wavelength.
• These frequencies are represented on the
electromagnetic spectrum.

5
The electromagnetic spectrum
6
All electromagnetic waves move at the speed of
light
• All forms of electromagnetic light travels at
light speed in a vacuum.
• The current accepted value for light speed is
2.99792458 X 108 m/s (or 3.0 x 108 m/s)
• The equation to determine wave speed is
• Cfl
• Which translates
• speed of lightfrequency X wavelength

7
Illuminance decreases as the square of the
distance from the source
• The rate at which light is emitted from a source
is called the luminous flux and is measured in
lumens (lm)
• The luminous flux decreases as you move away from
the light source.

8
To recap
9
Mirrors (Sections 2-3)
• Reflection the change in direction of an
electromagnetic wave at a surface that causes it
to move away from the surface
• Angle of incidence the angle between a ray that
strikes a surface and the line perpendicular to
that surface at the point of contact
• Angle of reflection the angle formed by the
line perpendicular to a surface and the direction
in which a reflected ray moves
• Virtual image an image that forms at a point
from which light rays appear to come but do not
actually come
• Concave spherical mirror a mirror whose
reflecting surface is a segment of the inside of
a sphere
• Real image an image formed when rays of light
actually pass through a point on the image
• Convex spherical mirror a mirror whose
reflecting surface is an outward-curved segment
of a sphere

10
Mirrors
• Most of us already have a good understanding of
plane mirrors aka flat mirrors and reflection
with plane mirrors. Remember that the angle of
incidence and reflection equate to be the same
degree.

11
Convex Mirrors
• Although the angle of incidence and reflection
equate to be the same value in a flat mirror, the
angles change in a convex mirror due to the
outward sphere. This makes the light rays go out
into different directions in an organized manner,
thus giving a smaller image, but a wide angle
view. This is why optical engineers use convex
mirrors when a situation calls for a better view
of an area, such as in your passenger side

12
Concave Mirrors
• A concave mirror is a little harder to
understand. Imagine how when you look at the
inside of a spoon, how your image is upside down.
That is because when the light ray hits the
inward sphere, the rays are reflected to a focus
line, a line parallel to the initial light ray.
Once you move past the focal point, the area
where the light rays come together, the image
flips due to the fact that you are picking up a
flipped ray, where the top ray is now on bottom
and the bottom ray is now on top.

13
Chapter 14 - Refraction
• Refraction the bending of a wave front as the
wave front passes between two substances in which
the speed of the wave differs.
• Index of refraction the ratio of the speed of
light in a vacuum to the speed of light in a
given transparent medium.
• Lens a transparent object that refracts light
rays such that they converge or diverge to create
an image.
• Total internal reflection the complete
reflection that occurs within a substance when
the angle of incidence of light striking the
surface boundary is greater than the critical
angle.
• Critical angle the angle of incidence at which
the refracted light makes an angle of 90 with
the normal (where refraction stops and reflection
begins).
• Dispersion the process of separating
polychromatic light into its component
wavelengths
• Chromatic aberration the focusing of different
colors of light at different distances behind a
lens.

14
Refraction
• Refraction is the bending of a wave as it enters
a new medium at an angle.
• When a wave enters a medium at an angle,
refraction occurs because one side of the wave
moves more slowly than the other side.
• Refraction only occurs when the two sides of a
wave travel at different speeds.

15
If light travels from one transparent medium to
another at any angle other than straight on, the
light ray changes direction when it meets the
boundary. In case of reflection, the angles of
incoming and refracted rays are measured with
respect to the normal. When studying refraction,
the normal line is extended into the refracting
medium. When light moves from one medium to
another, part of it is reflected and part is
refracted.
16
Index of Refraction
• An important property of transparent substances
is the index of refraction. Index of refraction
is the ratio of the speed of light in a vacuum to
the speed of light in a given transparent medium.
• Index of refraction Speed of Light (in vacuum)
• Speed of Light (in medium)

17
Snells Law
• Snells law determines the angle of refraction
• The index of refraction of a material can be used
to figure out how much a ray of light will be
refracted as it passes from one medium to
another. The greater the index of refraction, the
more refraction occurs.
• The angle of refraction was first found in 1621
by Willebrord Snell, who experimented with light
passing through different media. He then
developed a relationship called Snells law,
which can be used to find the angle of refraction
for light travelling between any two media

18
Snells Law
• Snells Law nisin?i nrsin?r
• (Index of refraction of incident material) times
the sin(incident angle in degrees) is equal to
(index of refraction of refractive material)
times the sin(refracted angle in degrees)

19
Sample Problem
• A light ray of wavelength 589 nm (produced by a
sodium lamp) traveling through air strikes a
smooth, flat slab of crown glass at an angle of
30.0 to the normal. Find the angle of
refraction, Tr.
• Given Ti 30.0 ni 1.00 nr 1.52
• Unknown Tr
• Solve nisin?i nrsin?r nisin?i / nr sin?r
?r sin-1(nisin?i / nr) ?r
sin-1(1.00)(sin30.0)/1.52 ?r 19.2

20
Lenses
• Lenses, in a sense, are the complete opposite
of mirrors, they use refraction, which is the
bending of light as it goes from one medium to
the next, to make a focal point, or spread out a
view.

21
Convex Lenses
• Convex Lenses are the complete opposite, in
theory, of convex mirrors. They too have an
outward sphere appearance, but instead use
refraction to create a focal point, compared to a
convex mirror which spreads out the light rays to
make a larger image. A good example of this would
be positive lens glasses, or close up glasses.
They center the light into a common focal point
and make things easier to distinguish close up.

22
Concave Lenses
• Concave Lenses are the complete opposite, in
theory, of concave mirrors. They too have an
inward sphere appearance, but instead use
refraction, again the bending of light as it goes
from one medium to the next, to spread out the
light rays and create a larger image. A good
example of this would be a tube television, the
screen is concave, which makes the image spread
out throughout the whole room, making things
easier to see.

23
Ch. 15 Interference Diffraction
• Coherence the correlation between the phases of
two or more waves
• Path difference the difference in the distance
traveled by two beams when they are scattered in
the same direction from different points
• Order number the number assigned to
interference fringes with respect to the central
bright fringe
• Diffraction a change in the direction of a wave
when the wave encounters an obstacle, an opening,
or an edge
• Resolving power the ability of an optical
instruments to form separate images of two
objects that are close together
• Laser a device that produces coherent light at
a single wavelength

24
Interference
• There are two types of wave interference
constructive and destructive
• In constructive interference, waves combine to
form a resultant wave with the same wavelength
but a greater amplitude than either of the
original waves.
• In destructive interference, waves combine to
form a resultant wave whose resulting amplitude
is smaller than the original and whose wavelength
is not the same as it was
• There are formulas for calculating constructive
and destructive interference d sin T m?
(constructive) and d sin T (m½)?
(destructive).

25
Diffraction
• Diffraction is a change in the direction of a
wave when the wave encounters an obstacle, an
opening, or an edge.
• A wave diffracts more if its wavelength is large
compared to the size of an opening or obstacle.