Download Material overview for the Exam #1

500nm
0.5µm
650nm
0.65µm
0.4µm
400nm
nano, written n, means 10-9. So the wavelength of yellow light is 500 nanometers = 500 nm
mega, written M, means 106. So a 100 MHz FM station is generating waves at 108 Hz
micro, written µ, means 10-6. So the wavelength of light is 0.5 micrometers = 0.5µm
milli, written m, means 10-3. So 1/1000 of a meter is a millimeter, or 1mm
Scientific Notation
Waves - the Electromagnetic Spectrum
!
!
Waves can be either Periodic or Aperiodic
Aperiodic wave
Periodic wave
space
Periodic wave
!
!
Periodic wave
space
Periodic wave
For periodic waves, we can identify a wave length, !, by measuring the
distance between unique points
Wavelength
and is the number of times per second that an
oscillation occurs at any fixed point in space
! = 1/"
The frequency,!, is the inverse of the period i.e.
the time taken for a wavelength ! to pass a given point -
For periodic waves, we can identify a period, T, by measuring
Period and Frequency
v = #!
speed = Wavelength x frequency
speed = Wavelength/Period
speed = distance/time
For periodic waves, we can identify a speed, v, by
Wavelength, Frequency, and Velocity
Or knowing the wavelength, we can calculate the frequency
So knowing the frequency, we can calculate the wavelength
So => c = #! or #=c/! or !=c/#
v = #!
Speed = Wavelength x frequency
Speed = Wavelength/Period
For periodic waves, we can identify a speed, v, by
Speed = distance/time
Wavelength, Frequency, and Velocity
In vacuum
dis tan ce !
speed = c =
= = !f
time
T
NOTE: The umbra is usually about 200km wide
Solar eclipse as viewed from space
Lunar eclipses
Diffuse reflections
Specular reflections
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/reflection/specular/index.html
Picture from text
How we see an image
• What do you notice about these reflections?
EXAMPLES OF REFLECTION - REFLECTIONS
n=
So n = c/v or v = c/n
speed of light in vacuum
speed of light in substance
NOTE: We define the index of refraction (n) of a
substance as -
Answer: The speed of light is slower in denser materials
Question: What determines if one material is more or less
dense than another from the point of view of light?
Density (optical) of selected materials
APPLET
http://micro.magnet.fsu.edu/primer/java/speedoflight/index.html
Speed of light in different materials
http://acept.la.asu.edu/PiN/rdg/refraction/refraction.shtml
• This is like when a marching band needs to make a turn
• Light waves incident on glass change direction and wavelength
when transmitted into the glass because the part of the wave in the
medium begins to slow down, causing the light beam to bend.
Light slows down in denser materials
http://csep10.phys.utk.edu/astr162/lect/light/ref-diff.html
The apparent and actual positions of the fish differ because
the direction of light propagation has been changed as light
passes (refracts) from the more dense water into the less dense air.
Refraction - Real Depth and Apparent Depth
refracted ray
glass or water
reflected
ray
incident
rays
• For incident angles in glass/water greater than the critical angle, ALL the light is
reflected back into the dense substance
• As the angle on the water side increases, the angle on the air side eventually goes past
90 degrees, which means that the light stays in the water! This happens at the critical
angle
• Examples - light going from glass-to-air or water-to-air
• Total internal reflection happens when light is incident from a more dense medium to a
less dense medium at a large angle of incidence
TOTAL INTERNAL REFLECTION
http://acept.la.asu.edu/PiN/rdg/refraction/refraction2.shtml
The internal reflectance at an air/glass interface for light rays from a point source in
glass. Light rays incident at angles to normal at greater than the critical angle (here, 41°
for glass to air) do not leave the material and are reflected at the glass/air interface.
TOTAL INTERNAL REFLECTION
Images in concave mirrors
• RULE #3: Incident rays headed for F are reflected so that they are parallel to the axis.
• RULE #2: Incident rays coming towards the center of curvature are reflected back on
themselves
• RULE #1: All rays parallel to the axis are reflected such that they appear to come from the
focal point F
How do we make images using spherical mirrors?
Images in concave mirrors
C. Using a different rule
B. Using the law of reflection
A. By drawing them close to the existing rays
How would you draw in other rays e.g. purple rays?
Images in concave mirrors
• RULE #3: Incident rays headed for F are reflected so that they are parallel to the axis.
• RULE #2: Incident rays coming towards the center of curvature are reflected back on
themselves
• RULE #1: All rays parallel to the axis are reflected such that they appear to come from the
focal point F
How do we make images using spherical mirrors?
Images in convex mirrors
• RULE #3: Incident rays headed for F are reflected so that they are parallel to the axis.
• RULE #2: Incident rays coming towards the center of curvature are reflected back on
themselves
• RULE #1: All rays parallel to the axis are reflected such that they appear to come from the
focal point F
How do we make images using spherical mirrors?
http://micro.magnet.fsu.edu/primer/java/lenses/converginglenses/i
ndex.html
Imaging with lenses
Magnification = Size of image = Image distance
Size of object Object distance
Magnification
More Ray Tracing in Lenses