10.2 Properties of Light and Reflection

Reflection When light (electromagnetic waves) hits a

surface its direction is changed

This change in direction is referred to as reflection.

Reflection can be seen best on surfaces that are mirrors or have mirror like properties.

Rays of Light

Light travels along a medium. A medium is a term that refers to a substance

through which light is traveling through (e.g. water, air)

Light will travel in a straight line as long as its moving through the same medium Therefore, if light is travel through air, it will travel

in a straight line However, if light travels through air then through

water, it may no longer travel in a straight line.

Predicting the Path of Light By understanding the properties of light and

mediums we can predict the path of light and also the formation of shadows

A ray is used to predict the path of light A ray is a straight line with an arrowhead that

shows the direction in which light waves are travelling.

Rays are commonly used in a process call ray tracing.

Ray Tracing Ray tracing is the process of drawing rays

from a light source to one or more objects.

Shadows can be detecting using this strategy

Fermat’s Principle Fermat’s principle predicts the path light will

take after reflecting from a surface or passing through more than one medium (e.g. air to water) Light will follow the shortest path possible

Leads to the laws of reflection

The Laws of Reflection A ray of light moving towards a surface is

known as the incident ray. The angle of incidence is the angle between

the incident ray and a perpendicular (Normal) line at the point where the ray touches the surface

The Laws of Reflection

The reflected ray begins at the point of contact and is at a right angle to the incident ray.

The angle of reflection is the angle between the reflected ray and the perpendicular (Normal) line.

The angle of incidence/ray is equal to the angle of reflection/ray Laws of reflection

Drawing Ray Diagrams Follow figure 10.14 and draw a ray diagram

for: An incident ray at 5 cm from the normal at a 30o

angle An incident ray at 10cm from the normal at a 20o

angle

Homework QuestionsAnswer questions 2-3 on page 414

Images in Plane Mirrors When light is applied to an object in a plane

mirror, the image of that object is formed on the other side.

Using the laws of reflection, one can predict the characteristics of the image and where the eye sees the image.

Image

Four Characteristics of an Image In general an image has four

characteristics:

1. Its location (i.e. closer than, farther than, same distance)

2. Orientation (upright or inverted)

3. Size (same, smaller, or larger)

4. Type (real or virtual)

E.g. Location (farther than)

E.g. Orientation (inverted)

Size (larger)

Type (real image)

Homework Questions Answer questions on page 418` #1,2,4, 6,7