5.1 The Ray Model of Light

• Some properties of light are best described by considering light as a wave. Other properties of light are best described by considering light as a particle.

• The ray model of light uses a straight line, or ray, to show the direction the light wave is traveling.

(c) McGraw Hill Ryerson 2007

Light and Matter

• Different materials can either transmit, absorb, or reflect light.

• Transparent materials allows light to pass through freely.

• Translucent materials lets most light through but scatters the light leaving.

• Opaque materials prevent light from passing through.

See pages 169 - 170

Light and Matter

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

Shadows

• A shadow is created when an opaque object absorbs light rays.

• Shadows demonstrate that light travels in straight lines.

See page 171

Shadows

• A ray diagram shows how the distance from the light source affects the size of the shadow an object makes.

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

Light Can Be Reflected

See page 172

• Reflection is when light bounces off of an object. To act like a mirror, the surface

must be smooth.

• The incoming ray of light is called the incident ray.

• The ray that bounces off the surface is called the reflected ray.

Incident rayReflected ray

Light Can Be Reflected

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

The Law of Reflection

See page 173

• The normal is an imaginary line perpendicular to the surface.

• The angle of incidence is measured from the normal to the incident ray.

• The angle of reflection is measured from the normal to the reflected ray.

The angle of incidence equals the angle of reflection.

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Light Can Be Refracted

See page 174

• When light travels from one transparent medium to a transparent medium it changes speed. This change in speed causes the light

to change direction.

• The bending of light, due to a change in speed, is called refraction.

• The angle of refraction is measured from the refracted ray to the normal.

(c) McGraw Hill Ryerson 2007

Refraction of Light in Water and Air

• Objects in water appear in a different location than they actually are. This is due to the refraction of the light.

• Light refracts when it passes through air at different temperatures. For example, a mirage is the light

from the sky bending as it approaches the warm air near the ground.

See page 175

(c) McGraw Hill Ryerson 2007

Refraction of Light in Water

See page 175

(c) McGraw Hill Ryerson 2007

Refraction of Light in Air

See page 175

Take the Section 5.1 Quiz