Lenses and Mirrors

How does light interact with pinholes? How does light interact with lenses? –___________ How does light interact with mirrors? –___________ We can use the _____________. Refraction Reflection photon model

Pinholes A ________ can be used to form an image. Light rays from point source screen pinhole

Image formation with a Pinhole camera Image is _______ if pinhole is larger Image is ________ if pinhole is smaller Image is __________ is pinhole is smaller Light source Dark room = Camera dimmer sharper fuzzy

Mirrors Flat Concave Convex

The Law of Reflection For reflection the _____________  i equals the _______________  r   i    r The angles are measured relative to the _________, shown here as a dotted line. incident angle reflected angle normal

Forming Images with a Plane Mirror A mirror is an object that reflects light. A _______ mirror is simply a flat mirror. Consider an object placed at point P in front of a plane mirror. An image will be formed at point P´ behind the mirror. dodo didi For a plane mirror: d o = -d i and h o =h i hoho hihi d o = distance from object to mirror d i = distance from image to mirror h o = height of object h i = height of image plane

Images An image is formed at the point where the rays of light leaving a single point on an object either _________ intersect or from where they ________ to originate. actually appear

Images If the light rays actually do intersect, then the image is a __________. If the light only appears to be coming from a point, but is not physically there, then the image is a _____________. real image virtual image

Images We define the ____________, m, of an image to be: If m is negative, the image is inverted (upside down). magnification

Spherical Mirrors A _________ _______ has a surface shape with radius of curvature R. There are two types of spherical mirrors: _______ and _______. ________ spherical mirror concave convex concave convex

Focal Point When ________ rays (e.g. rays from a distance source) are incident upon a spherical mirror, the reflected rays ________ at the _________ F, a distance R/2 from the mirror. For a ________ _______, the focal point is in front of the mirror (_____). parallel intersectfocal point concave mirror real

Focal Point The incident rays ______ from the _______ _______, but they trace back to the focal point F. For a ____________, the focal point is behind the mirror (________). convex mirror virtual diverge convex mirror

Focal Length The _______________is the distance from the surface of the mirror to the focal point. It can be shown that the focal length is half the radius of curvature of the mirror. Sign Convention: the focal length is negative if the focal point is behind the mirror. For a concave mirror, f = ____ For a convex mirror, f =  ___ (R always +) focal length (f) ½ R

Ray Tracing It is sufficient to use ______ principal rays to determine image location. The parallel ray (P ray) reflects through the focal point. The focal ray (F ray) reflects parallel to the axis, and the center-of-curvature ray (C ray) reflects back along its incoming path. three

Ray Tracing – Examples concave convex Virtual image Real image Put film here for Sharp image.

Lenses Concave Convex –Refraction

Reflection and Refraction When a light ray travels from one medium to another, part of the incident light is _________ and part of the light is _____________ at the boundary between the two media. The transmitted part is said to be __________ in the second medium. incident rayreflected ray refracted ray reflected transmitted refracted

Red Light

Lenses Light is reflected from a mirror. Light is __________ through a lens. refracted

Focal Point The ___________ of a lens is the place where parallel rays incident upon the lens ________. _____________________________ focal point converge Diverging lensConverging lens

Ray Tracing for Lenses P ray travels parallel to the principal axis until lens, it refracts to pass through the focal point on the far side of the lens. The F ray passes through the focal point on the near side of the lens, leaves parallel to the principal axis. The M ray passes through the middle of the lens with no deflection. Just as for mirrors we use three “easy” rays to find the image from a lens.

Focal Length

26: Geometrical Optics