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 anglereflected angle

normal

Forming Images with a Plane MirrorA 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.

do diFor a plane mirror:

do = -di and ho =hi

hohi

do = distance from object to mirror

di = distance from image to mirror

ho = height of object

hi = 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.

actuallyappear

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:

o

i

o

i

d

d

h

hm

heightobject

height image

If m is negative, the image is inverted (upside down).

magnification

Spherical MirrorsA _________ _______ has a surface shape with radius of curvature R. There are two types of spherical mirrors: _______ and _______.

________

________

sphericalmirror

concaveconvex

concave

convex

Focal PointWhen ________ 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

intersect focal point

concavemirror

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

convexmirror

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

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 imageReal image

Put film here for

Sharp image.

Lenses

• Concave

• Convex

–Refraction

Reflection and RefractionWhen 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 ray reflected ray

refracted ray

reflectedtransmitted

refracted

Red Light

Red Light

Red Light

Lenses

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

refracted

Focal PointThe ___________ of a lens is the place where

parallel rays incident upon the lens ________.

_______________ ______________

focal pointconverge

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

• http://www.physics.odu.edu/hyde/Teaching/Spring04/Lectures/318,1,Chapter 26: Geometrical Optics