Reflection of Light

Reflection: the turning back of a wave after meeting the boundary of a medium

Regular Reflection

Types of Behaviors:

transmitted

absorbed

Scattered reflection

Animations courtesy of Dr. Dan Russell, Kettering University

Mirror: an object that produces regular reflection at a high percentage of reflectance.

Types of Mirrors

A) Plane: Reflective surface lies in a plane

B) Convex: Outside curve of the mirror is reflectiveC) Concave: Inside curve of the mirror is reflective

Types of Images

Real image formed by light rays that actually converge through the image point.

**Real images can only be formed by concave mirrors!

Virtual image is formed behind the mirror by reflected light rays that diverge, but appear to meet behind the mirror.

**Virtual images are formed by plane, convex and concave mirrors!

Plane Mirror Image

always form a virtual image that appears the same size as the object, and just as far behind the mirror as the object is in front.

Plane Mirror Image:

hi = ho and

di = do

Always virtual and:

What is unusual about this picture?

The picture is upside down!

Convex Mirror Image:

Always Virtual and…

hi = di

ho do

hi < ho

and

di < do

But in proportion

to each other:

Concave Mirror Image:

As the object approaches the mirror:

A smaller real image is formed, then

A same size real image, then

No image at all, then

Virtural image (hi > ho)

hi = di

ho do

Again:

Curved Mirror Terminology

vertexprincipal axis F

Principal Focus

C

Center of Curvature

focal length (f)

radius of curvature (r) r = 2f

F

di

do

1 = 1 + 1

f do di

hi = di

ho do

Concave

Mirror

Image

Formation

Convex

Mirror

Image

Formation

do

F

di

Virtual distances cannot actually be measured!

Virtual distances are negative!• f is always negative for a convex mirror

• di is always negative for a virtual image

A man places an object 5.0 m in front of a plane mirror and plans to photograph the image of the object in the mirror. How far away from the lens should the camera be focused to produce the clearest possible image?

A face that is 28.0 cm long is moved in front of a concave make-up mirror. If the focal length of the mirror is 20.0 cm, and the face is 15.0 cm from the mirror, how tall will the image be?

A convex shoplifting mirror makes an image of a 1.85 m man appear to be only 45.0 cm tall. What is the focal length of the mirror?

A candle that is 12.0 cm tall is placed in front of a concave mirror so that the image of the object is projected onto a screen. The image is measured to be 12.0 cm tall. What is the focal length of the mirror?

A man whose eyes are 1.62 m above the floor stands 2.10 m in front of a plane mirror whose bottom edge is 43.0 cm above the floor. How much closer to the mirror must the man move in order to see his feet in the mirror?

A student uses a concave mirror of focal length 7.60 cm located at the 80.00 cm mark on the optical bench. His object is located at the 68.00 cm mark. At what mark should he place his screen in order to see the real image produced?

An object that is 2.00 cm tall is placed in front of a concave mirror and produces a virtual image that appears 5.45 cm tall. If the image is placed 7.00 cm in front of mirror, what must be the focal length of that mirror?