SPH 3UO LESSON PLANS

Text: Physics 11 (Addison-Wesley)

Characteristics of Light:
Light ...is the form of radiant energy that our eyes are sensitive to
Luminous Objects produce light (ex. sun)
Non-luminous Objects: reflect light but produce none of their own.

Characteristics of Light:
1) Straight-Lines (shadows and eclipses)
2) very fast
3)as a wave?

Transparent: transmit light easily (window)
Opaque: do not permit light to pass (wood)
Translucent: some light is transmitted (frosted glass)

The Plane Mirror...The two laws of relfection
1) The angle of reflection is equal to the angle of incidence
2) The incident ray, normal and relected ray all lie on the same plane
The angle of incidence and reflection are measured from the normal
A ray that is aimed straight towards the mirror has an incident angle of 0^o and is reflected back with the same ange of reflection.
Therefore it is reflected back into itself.
What is the shortest mirror you can use to see your entire body in the mirror?
-If the mirror is hung properly it only needs to be half of your height
-the mirror must be hung so that the top of the mirror is halfway between your head and your eyes
-the bottom of the mirror is halfway between your eyes and your feet
If hung at this height you will be able to see your entire reflection at any distance from the mirror.

Image Characteristics (in general)
1. Magnification: How does the size of the image compare to the size of the object?
M = h_i / h_o ...
2. Attitude: Is the image upright or inverted?

3. Type: Is the image virtual or real? If the image can be projected onto a screen
(if the light rays are actually there then the image is real...Otherwise the image is virtual)

4. Location: Is the image in front or behind the optical device?

Image Characteristics (plane mirror)
1. Magnification is 1. The object and the image are the same size.
2. Upright. Your image is not upside down.
3. Virtual. The image is behind the mirror although no light is actually back there.
4. Behind. The image forms behind the mirror.

Curved Mirrors...Types of Curved Mirrors
1) Spherical Mirror is part of a sphere, with a convex surface (outside of sphere) and a concave surface (inside of sphere)
2) Cylindrical Mirror is part of a cylinder (convex = outside, concave = inside)
3) Parabolic Mirrors also exist

Curved mirror jargon...
converging mirror: parallel rays come to a focus
diverging mirror: parallel rays spread apart
center of curvature "C": center of the sphere or cylinder
radius of curvature "r": distance from the center of curvature to the mirror
vertex "V": the geometric center of the mirror
principal axis "PA": a line through V and normal to the surface
focal point "F": the point where all the rays parallel to PA meet
focal length "f": the distance from F to the mirror

Rays Diagram for Curved Mirrors...
Three special rays:
1) a ray that travels parallel to PA is reflected through F
2) a ray that passes throught F is reflected parallel to PA
3) a ray that passes through C is reflected back onto itself

Drawing Ray Diagrams
Ray diagrams are used to find the image of an object in front of a curved mirror
1) draw a scale diagram of the object and mirror
2) from the top of the object draw the three special rays reflecting off of the mirror
3) these reflected rays (all three) should converge onto a point. This is where the top of the image is.
4) Describe the four characteristics of the image.

Speed of Light
Initially attempts to measure the speed of light concluded that it was either infinite or so fast that human reaction time would not allow for measurement.
First accurate measurement was by Albert Michelson, and found to be 2.99798 x 10⁸ m/s
The speed of light is different in different materials
Material              c
vacuum               3 x 10⁸ m/s
air                       3 x 10⁸ m/s
water                  2.3 x 10⁸ m/s
glass                   2 x 10⁸ m/s

Index of Refraction
Is the ratio of how fast light travels in the medium compared to light traveling in a vacuum...n=c/v

Material               c
vacuum                1
air                       1
water                   1.33
glass                   1.5

-all light travels at the same speed in a vacuum but in materials different colours travel at different speeds
-red light travels 1% faster than blue light in glass
-the tables are for yellow light so the other colours are slightly different

Critical Angle and total Internal Reflection...
A ray travelling from a more refractive to a less refractive medium at some incidence angle where i<Oc
i=r and R>i
As i gets bigger so does R until at some critical angle the refracted ray is at 90^o.
call this angle of incidence Oc when R = 90^o.
If i is greater that Oc then there is no refracted ray and all the light is reflected back
This is called total internal reflection and the conditions for it to occur are:
1) light must be travelling in the more refractive index
2) the angle of incidence must be greater than the critical angle
To calculate the critical angle Snell's Law turns into sinOc = n₂/n₁ ...
Most optical instruments use TIR to reflect light instead of mirrors because...
1) mirrors corrode
2) mirrors break
3) mirrors do not reflect light as efficiently as TIR

Colour Theory... Newton found that white light passes through a prism splits up into the spectrum of colours
He showed that white light is composed of all of these colours
He split up the spectrum into seven colours (ROYGBIV)
Violet light refracts (bends) more than red light does
Newton also showed that dispersed light can be recombined

You don't need all colours to make white light. You only need three (primary colours)
Primary colours...red, green, blue (ex. T.V. monitors)
Secondary colours...yellow, cyan (aqua), magenta (purple)
Complementary Light Colours: one primary and one secondary = white light
Additive Colour mixing...means that red, green and blue stage lights can produce white light as well as any other colour.

Why does a rose look red?
1) white light hits the rose
2) rose absorbs all but he red
3) red light is reflected off the rose
4) you see the red reflected light and the rose appears red
Filters work in the same way. For example a blue filter would absorb all light except blue, and allow the blue to pass through.

Ray Diagrams for Lenses
Converging lenses are thickest in the middle
-These focus light to a common point called the real principal focus
Diverging lenses are thinnest in th middle
-These diverge fays from a point behind the mirror called the virtual principal focus

Principal axis (PA) runs through the center of the lens and perpendicular to both surfaces
The focal length is the distance along the PA where both focuses appear
For a converging lens the primary focus PF) is behind the lens and for a diverging lens the primary focus is in front of the lens.

Rules for a ray diagram...
-Represent the lens by a straight line with a symbol in the middle showing what type of lens it is
-Measure and label the primary focus and secondary focus
-ray #1 - a ray parallel to PA passes through the PF
-ray #2 - a ray passing through the center of the lens goes straight throught
-ray #3 - a ray that passes through the SF emerges parallel to the PA

Thin Lens Equations
1/d_o +  1/d_i = 1/f ...
d_o = distnace of the object from the lens
d_i = distance of the image from the lens
f = focal length of the lens
m= - d_i /d_o ... wher m = magnification
recall m=h_i /h_o ...
sign conventions - f is positive for convergin g lenses and negative for diverging lenses
- the object distance d_o  is always positive
-the image distance d_i  is positive for real images and negative for virtual images
-the image height h_i  and object height h_o are positive when pointing up and negative when pointing down
-the magnification m is positive when the image is upright and negative when the image is inverted

example: A 3:00 cm tall figurine is placed 7.10 cm to the left of a diverging lens of focal length 5.08 cm. Describe the image.