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Chapter 34: Geometric Optics (Plane Mirrors (General (How light works…
Chapter 34: Geometric Optics
Plane Mirrors
General
How light works
Light comes in from outdoors or is scattered from an object hits the mirror and comes back to our eye
The reason it looks like the object is behind the mirror is the way our eyes work
We're really looking at the reflected light and if we trace back those rays it forms a point behind the mirror
This is the
image
Our eyes extrapolate that the object is there.
Properties
An image can act as an object for a second surface
Point vs Extended
Misc.
Terms
Object: something that radiates light
Point vs Extended
Point object: Has no physical extent
Types of Reflection
Smooth
Image
2 more items...
Diffuse
Extended Object: Real life objects, they have dimensions (height,length,width)
Reflection
An object diverges light
It reflects off the (smooth) mirror with the law of reflection
It reaches our eyes. Since it reaches our eyes at different angles we perceive a distance from us and the object
The rays that reach us are the reflected rays and the distance we perceive depends on where those reflected rays end up as we follow them back
This is how depth perception works
Refraction
This occurs only when there's a difference in material
The light bends as it enters the interface
If we're on the opposite side of the object then wherever the refracted rays are traced back is where the object appears to be(the image)
Expectations
If we looked at yourself in a typical mirror we'd expect to see our self with the same height we are
In other words we are not magnified \(m=\frac{y^{\prime}}{y}\)
We are reversed but not from left to right.
We call the directions left-right, up-down, back-front
Looking at it from where our hand is it looks like our index and middle finger point in the same direction, but the thumb does not
Our thumb points away from us while in the mirror it points towards us
Therefore mirrors reflect from front to back not left to right
In physics terms we need describe it with 3 qualities: upright,same size, virtual
virtual
again just means that no real light rays pass through the image
There isn't actually an object behind the mirror
Concepts
Lens and Mirrors make you see things that arent really there
With a mirror it looks like you see something behind the mirror
All use the idea of law of reflection and refraction or the combination of two
Telescopes and microscopes make something look much closer than they actually are
Kaleidoscopes makes it look like there's multiple copies of an object
Spherical Surface
General
The downside with mirrors is that they always have an image with the same size as the object
What if we wanted to magnify an object?
What if we wanted to make them smaller so they could fit on a tv screen?
Properties of a spherical mirror
Center of curvature
: If we imagine the mirror as a full sphere the center of curvature represents the radius of that sphere
Focal Point
: If we have parallel rays hitting the mirror all those rays will come from or seem to come from one point. We call this the focal point
Object Distance
: Just like with plane mirrors object distance is the distance of the mirror away from the object
Image Distance
: Distance from the mirror to the image
Magnification
: Refers to the size and orientation change of the image.
Negative if inverted.
1 if enlarged
<1 if shrunk
Convex
Concave
Reflection
Refraction
Lens
General
Usefulness
Properties
Derivations
Reflection at a Spherical Surface
We now use the following theorem from plane geometry: An exterior angle of a triangle equals the sum of the two opposite interior angles
Problem Solving
Thin Lens
Converging lens' have \(R_1\)=+ and \(R_2\)=-
Camera
Converging Lenses
