Geometric Optics

Uses wave model of light to explain properties such as reflection and refraction Assumptions of geometric optics - light travels in straight lines - ray: path taken by light

Pinhole Camera Simplest version of a camera consisting of a box with a small opening Light ray passing from the top of an object go through the hole and hit the back of the box Light ray passing from the bottom of the object go through the hole and hit the back

Image Characteristics Real Image – can be formed on a screen; not virtual Image smaller than object Image is inverted If photographic film placed on the back of the box, picture is permanent

Equation h i = d i h o d o h i - height of image d i – distance of image h o – height of object d o – distance of object

Magnification (M) M = h i h o If M > 1, image is enlarged If M < 1, image is reduced

Example What is the size of the image of a 8.0 m high tree which stands 80 m in front of a 20cm long pinhole camera? What is the magnification?

Reflection When light rays hit an opaque (not transparent) surface, they are reflected Law of Reflection angle of incidence = angle of reflection i = r

normal ir

Diffuse Reflection When light reflected from uneven surfaces reflect in many directions (no image can form)

Images When parallel rays of light are reflected parallel, an image can form Image formed is virtual (not real) and appears at the same distance behind the mirror as the object is in front (d i = d o ) Image formed is the same height as the object (h i = h o )

Brains Role Light ray from the object hits the mirror and reflects to the eye Brain assumes that light travels in a straight line so we believe the reflected light originated somewhere behind the mirror

Image Characteristics Virtual Same size Erect Laterally inverted

Example A 1.60m tall person stands in front of a vertical mirror. What is the minimum height of mirror needed for him to see his entire body? How high must it be off the floor? (assume the eye is 10cm below the top of his head)