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Chapter 13 The Characteristics of light

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

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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
    electromagnetic radiation.
  • 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
    forms of radiation.
  • 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
    mirrors on your car.

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.
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