Unit 4 Optics: Properties of Light and Reflection

Unit 4 Optics: Properties of Light and ReflectionSNC2D1 Grade 10 ScienceLuminous objectsRadiate light in all directionsRepresented by a light ray on a diagram line & arrowshows direction light waves travel inLight emitted from a source is called the incident light

Light travels in a straight line as it is moving through the same medium. Medium: the substance through which light travels (air, water, glass, etc.)

Light determines a property of matter, depending on how it strikes it. Matter can be classified into 3 categories:Transparent: material that transmits all incident light; objects are seen through the material.

Translucent: material that transmits some incident light but absorbs or reflects the rest; objects are not clearly seen through the material.

Opaque: material does not transmit any incident light; all incident light is either absorbed or reflected. Object behind the material can not be seen.ShadowsOpaque objects will not allow light to pass through, and therefore cast a shadow, outlining the edge of the object with light

Umbra: Darkest part of the shadowPenumbra: Region wheresome or allof the light source is obscured

Reflectionthe change in direction of a wave when it reaches a surface and bounces off that surface.

ReflectionSpecular (Regular): reflection off a smooth, shiny surfaceE.g. plane mirror, still water

Diffuse: reflection of light off a irregular or dull surface

A mirrorAny polished surface that exhibits reflection.2 parts:front = sheet of glassback = thin layer of reflective silver or aluminum

An image: reproduction of an original object through the use of light

Mirrors

objectimageIt is possible to see images in mirrors.Reflection (bouncing light)Reflection is when light changes direction by bouncing off a surface.

When light is reflected off a mirror, it hits the mirror at the same angle (the incidence angle, i) as it reflects off the mirror (the reflection angle, r).

The normal is an imaginary line which lies at right angles to the mirror where the ray hits it.ri

Mirrornormalincident rayreflected ray

The Laws of ReflectionThe angle of incidence = The angle of reflectionThe incident ray, reflected ray, and the normal all lie in the same plane.

Lets draw our own ray diagram!Ray diagrams

Draw the diagram with the class on the white board to show the steps of drawing ray diagrams15

Mirrors reflect light rays.Images in Plane MirrorsImages seen in mirrors are VIRTUAL IMAGESAn image in which light does not actually arrive at or come from the image locationThis light only appears to come from the image

That is why we see the image in or behind the mirror

Images in Plane Mirrors(flat mirrors)

How do we see images in mirrors?

Images in Plane Mirrors(flat mirrors)

objectimageLight reflected off the mirror converges to form an image in the eye.How do we see images in mirrors?

Images in Plane Mirrors(flat mirrors)

objectimageLight reflected off the mirror converges to form an image in the eye.The eye perceives light rays as if they came through the mirror.Imaginary light rays extended behind mirrors are called sight lines.How do we see images in mirrors?

Images in Plane Mirrors(flat mirrors)

objectimageLight reflected off the mirror converges to form an image in the eye.The eye perceives light rays as if they came through the mirror.Imaginary light rays extended behind mirrors are called sight lines.The image is virtual since it is formed by imaginary sight lines, not real light rays.How do we see images in mirrors?

SALT is used to describe images formed by mirrors.S- Size: compared to original object is it same size, smaller or bigger?A- Attitude: which way the image is oriented compared to the original object (upright or inverted).L- Location: location of the image (in front or behind the mirror).T- Type: is the image a real image or virtual image?

S.A.L.T23S same as objectA uprightL behind mirrorT virtual Characteristics of a plane mirror image:

24The image in a plane mirror appears to be backwards compared to how we view the object directly.

This is why the word on the front of an AMBULANCE is written backwards- so it can be read when seen in a rear-view mirror.

AMBULANCE25