Geometric Optics Uses wave model of light to

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 hi = di ho do hi - height of image di – distance of image ho – height of object do – distance of object

Magnification (M) M = hi ho If M > 1, image is enlarged If M < 1, image is reduced

Example •

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 i r

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 (di = do) • Image formed is the same height as the object (hi = ho)

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