Geometric Opticsrfinn/phys140s09/Geometrical-Optics-1.pdf · General Physics 2 Geometric Optics 22...

General Physics 2 Geometric Optics 1

Geometric Optics

•  Ray Model •  assume light travels in straight line •  uses rays to understand and predict reflection &

refraction


Reflection

•  Law of reflection •  the angle of incidence equals angle of reflection •  angles are measured from normal


Reflection

Diffuse reflection Specular reflection


Think-Pair-Share

•  What would be the appearance of the Moon if it has •  (a) a rough surface? •  (b) a polished surface?


Plane Mirrors


Extra Credit

•  How large a mirror do you need to see your whole body?


Spherical Mirrors

By using ray tracing and the law of reflection, you can figure out where the incoming rays are reflected.


Focal Point & Focal Length

•  Parallel rays striking a concave mirror come together at focal point

f = r/2

r = radius of sphere f = focal length


Image Formation

Real Image


Mirror Equation & Magnification


Plug & Chug

•  How far from a concave mirror (radius 23.0 cm) must an object be placed if its image is to be at infinity?


Convex Mirrors

•  Virtual Image •  can’t detect on paper or

screen •  Sign Conventions

•  object, image, or focal point on reflecting side of mirror has a positive distance

•  Anything behind mirror has negative distance

•  image height is positive if upright, negative if inverted (relative to object)


Refraction

•  index of refraction, n, where c = speed of light in a vacuum and v = speed of light in that medium

•  nair = 1 •  nglass = 1.5

•  Snell’s Law


Indices of Refraction


Total Internal Reflection •  Incident angle where refracted angle (θ2) is 90 is the

critical angle

•  at incident angles greater than critical angle, light is totally internally reflected

important for fiber optic technology (endoscope)


Think-Pair-Share

•  What is the focal length of a plane mirror? What is the magnification of a plane mirror?


Lens Activity

•  Use the equipment provided to make an image of the light source on the screen.


Thin Lenses


Focal Length, Focal Plane and Power

•  f = focal length •  Power

•  inverse of focal length •  P = 1/f •  measured in diopter (D) •  1 D = 1 m-1


Ray Tracing


Thin Lens Equation

Thin Lens Equation Magnification


Sign Conventions •  focal length

•  positive for converging lenses •  negative for diverging lenses

•  object distance •  positive if the object is on the side of the lens from which the light is

coming (this is usually the case) •  otherwise, it is negative (virtual object).

•  image distance •  positive if the image is on the opposite side of lens from where light is

coming •  positive for real images, negative for virtual images

•  image height •  positive if image is upright relative to object, negative for inverted

images •  h0 is always positive


Lens Activity

•  Find two different object-image distances that create a real image. Describe any differences in the image properties.


Think-Pair-Share

•  Sunlight is observed to focus at a point 18.5 cm behind a lens. (a) What kind of lens is it? (b) What is its power in diopters?


Fermat’s Principle

•  When light travels between 2 points, its path is the one that requires the smallest time interval.


Combination of Lenses

•  When adding two or more lenses in series, the focal length of the combined lenses, f, is:


Combining Lenses •  Measure the focal length of the two double-convex lenses

individually. •  Combine the lenses together and measure the combined

focal length. •  Calculate the combined focal length using the equation.

•  Calculate the percent error of your measured value.

Geometric Opticsrfinn/phys140s09/Geometrical-Optics-1.pdf · General Physics 2 Geometric Optics 22...

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