Unit 4 Optics: Properties of Light and Reflection SNC2D1 – Grade 10 Science

Luminous objects Radiate light in all directions Represented by a light ray on a diagram line & arrow shows direction light waves travel in Light 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.

Shadows Opaque objects will not allow light to pass through, and therefore cast a shadow, outlining the edge of the object with light

Penumbra: Region where some or all of the light source is obscured  Umbra: Darkest part of the shadow

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

Reflection Specular (Regular): reflection off a smooth, shiny surface E.g. plane mirror, still water Diffuse: reflection of light off a irregular or dull surface

A mirror Any polished surface that exhibits reflection. 2 parts: front = sheet of glass back = thin layer of reflective silver or aluminum An image: reproduction of an original object through the use of light

Mirrors It is possible to see images in mirrors. image object

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, θi) as it reflects off the mirror (the reflection angle, θr). The normal is an imaginary line which lies at right angles to the mirror where the ray hits it. θr θi Mirror normal incident ray reflected ray

The Laws of Reflection The angle of incidence = The angle of reflection The incident ray, reflected ray, and the normal all lie in the same plane. Let’s draw our own ray diagram!

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

Mirrors reflect light rays.

Images in Plane Mirrors Images seen in mirrors are VIRTUAL IMAGES An image in which light does not actually arrive at or come from the image location This 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) object image How do we see images in mirrors? Light reflected off the mirror converges to form an image in the eye.

Images in Plane Mirrors (flat mirrors) object image How do we see images in mirrors? Light 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.

Images in Plane Mirrors (flat mirrors) object image How do we see images in mirrors? Light 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.

S.A.L.T 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?

Characteristics of a plane mirror image: S – same as object A – upright L – behind mirror T – virtual

The 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. AMBULANCE