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Light and ReflectionLight and Reflection
Chapter 14
Characteristics of LightCharacteristics of Light
Section 14.1
Electromagnetic WavesElectromagnetic Waves
Light is made of electromagnetic waves.Take a prism and break up white light into a rainbow
like band of colors. These are all in the visible spectrum.
Red, orange, yellow, green, blue, indigo and violet.ROY G BIV
Electromagnetic WavesElectromagnetic Waves
The spectrum also includes non-visible electromagnetic waves, such as x-rays, microwaves, radio waves, and radiation.
Because they all are electromagnetic waves they all have similar properties.
Electromagnetic WavesElectromagnetic Waves
Electromagnetic waves are transverse waves consisting of oscillating electric and magnetic fields at right angles to each other.
Oscillate: to have a periodic vibration
Electromagnetic WavesElectromagnetic Waves
Electromagnetic waves vary depending on frequency and wavelength
All electromagnetic waves move at the speed of light
Electromagnetic WavesElectromagnetic Waves
We will use 3.00 X 108 m/s as the speed of light, c.
The wave speed equation is:
c = f Speed of light = frequency X wavelength
Sample ProblemSample Problem
The AM radio band extends from 5.4 X 105 Hz to 1.7 X 106 Hz. What are the longest and shortest wavelengths in this frequency range?
f 1 = 5.4 x 105 Hz f 2 = 1.7 x 106 Hzc = 3.0 x 108 m/sc = f= c/ f
1 = 5.6 x 102 m
2 = 1.8 x 102m
Light travels in straight lines.Light travels in straight lines.
Light travels in straight lines.• Show the laser on the wall. Put an index card in
the beam. This shows that the light is traveling in a straight line, but you can only see it when it hits something.
• Put some chalk dust in the beam to show it is continuous.
Brightness decreases by the square of the distance form the source
• Show how the size of the dot the laser makes gets bigger as it gets further from the source.
Laser
The brightness of light is inversely proportional to the square of the distance from the light source.Ex. If you move twice as far away from the light source, ¼ as much light falls on the book.
Flat mirrorsFlat mirrors
Section 14.2
Reflection of LightReflection of Light
Reflection – the turning back of an electromagnetic wave at the surface of a substance
Clear vs. Diffuse ReflectionClear vs. Diffuse Reflection
Specular reflection: light reflected from smooth shiny surfaces
In specular reflection the incoming and reflected angles are equal (=’)
Diffuse reflection: light is reflected from a rough textured surface
Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
Reflection of LightReflection of Light
Angle of incidence – the angle between a ray that strikes a surface and the normal to that surface at the point of contact.
Angle of reflection – the angle formed by the line normal to a surface and the direction in which a reflected ray moves
Normal is a line perpendicular to the reflection surface.
The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection
In other words, light gets reflected from a surface at THE SAME ANGLE it hits it.
The same !
!!
Drawing a Reflected Drawing a Reflected ImageImage
Use ray diagrams to show image location
We will find the virtual image (the image formed by light rays that only appear to intersect)
Drawing a Reflected Drawing a Reflected ImageImage
Draw the object in front of the mirrorDraw a ray perpendicular to the mirror’s surface. Because this
is 0 from normal, the angle is the same from the mirror to the virtual object
Draw a second ray that is not perpendicular to the mirror’s surface from the same point to the surface of the mirror.
Next, trace both reflected rays back to the point from which they appear to have originated, that is, behind the mirror. Use dotted lines when drawing lines that that appear to emerge from behind the mirror. The point at which the dotted lines meet is the image point.
Flat MirrorsFlat Mirrors
Image is VIRTUAL, UPRIGHT, UNMAGNIFIED
Chapter 14Chapter 14
14.3 Concave Mirrors
Concave Spherical Concave Spherical MirrorsMirrors
A spherical mirror has the shape of part of a sphere’s surface. The images formed are different than those of flat mirrors.
Concave Spherical Mirror – an inwardly curved, mirrored surface that is a portion of a sphere and that converges incoming light rays.
Concave Spherical Concave Spherical MirrorsMirrors
The light bulb is distance p away from the center of the curvature, C. Light rays leave the light bulb, reflect from the mirror and converge at distance q in front of the mirror. Because the reflected light rays pass through the image point, the image forms in front of the mirror.
Concave Spherical MirrorConcave Spherical Mirror
When an object changes its location in relation to the mirror, its image changes in location, and form.
Spherical Mirrors - Spherical Mirrors - ConvexConvex
Convex spherical mirror:An outwardly curved, mirrored surface that is a portion of a sphere and that diverges incoming light rays
The focal point and center of curvature are situated behind the mirror.
Spherical Mirrors - Spherical Mirrors - ConvexConvex
Convex mirrors take the objects in a large field of view and produce a small image, but give a the observer a complete view of a large area.
Examples:In stores, the passenger’s side of a car
ColorColor
White light is not a single color; it is made up of a mixture of the seven colors of the rainbow.
We can demonstrate this by splitting white light with a prism:
This is how rainbows are formed: sunlight is “split up” by raindrops.
Wavelengths of LightWavelengths of Light
Red Light – nm
Green Light - nm
Blue Light - nm
Adding coloursAdding coloursWhite light can be split up to make separate
colors. These colors can be added together again.
The primary colors of light are red, blue and green:Adding blue and
red makes magenta (purple)
Adding blue and green makes cyan
(light blue)
Adding all three makes white again
Adding red and green makes yellow
Seeing colorSeeing colorThe color an object appears depends on the
colors of light it reflects.
For example, a red book only reflects red light:
White
light
Only red light is
reflected
A white hat would reflect all seven colors:
A pair of purple pants, in addition to being ugly, would reflect purple light
(or red and blue, as purple is made up of red and blue):
Purple light
White
light
Using colored lightUsing colored light
If we look at a colored object in colored light we see something different. For example, consider the outfit below – I mean, from a physics standpoint, not as a fashion choice:
White
light
Shorts look blue
Shirt looks red
In different colours of light this kit would look different:
Red
lightShirt looks red
Shorts look black
Blue
light
Shirt looks black
Shorts look blue
Using filtersUsing filtersFilters can be used to “block” out different colours of
light:
Red Filte
r
Magenta
Filter