Ray Model of Light Explains that light travel in straight lines Sources of light: sun, stars, fire, electrical storms, fireflies, jellyfish – bioluminescence, flaghlights, lamps, neon signs (c) McGraw Hill Ryerson 2007

This model is known as the Particle Model of Light. 5.1 The Ray Model of Light Newton thought of light as extremely small particles that traveled in a straight line until they entered an eye, where they were absorbed to make an image. This model is known as the Particle Model of Light. Parts of this model are still used today. Some properties of light are best described by considering light as a wave, such as the use of wavelength and frequency to account for the different colours of light. Issac Newton believed that light is a stream of fast-moving tiny particles that traveled in a straight line until they reached the eye where they were absorbed to make an image. See page 168 (c) McGraw Hill Ryerson 2007

5.1 The Ray Model of Light The Ray Model of Light is more simplified, it uses a straight line, or ray, to show the direction the light wave is traveling. Both models describe some properties of light but neither one describes of light’s properties. Some properties of light are best described by considering light as a wave, such as the use of wavelength and frequency to account for the different colours of light. Issac Newton believed that light is a stream of fast-moving tiny particles that traveled in a straight line until they reached the eye where they were absorbed to make an image. See page 168 (c) McGraw Hill Ryerson 2007

Different materials can either transmit, absorb, or reflect light. Light and Matter: Different materials can either transmit, absorb, or reflect light. See pages 169 - 170 (c) McGraw Hill Ryerson 2007

Transparent materials allow light to pass through freely. Transparent Objects Transparent materials allow light to pass through freely. They transmit light. Eg. Clear plastic bags See pages 169 - 170 (c) McGraw Hill Ryerson 2007

Some light absorbed and/or reflected Translucent Translucent materials lets most light through but scatters the light leaving. Some light absorbed and/or reflected Eg. Frosted glass, lampshade, wax paper. Often used in bathrooms. Why would we want this? Allow light in but maintain privacy. See pages 169 - 170 (c) McGraw Hill Ryerson 2007

Opaque materials absorb and reflect light Opaque materials prevent light from passing through. They absorb and reflect light. Wood, metal, cardboard, eyelids, books, aluminum foil Leaves dark shadow What is a shadow? What determines the size/length? See pages 169 - 170 (c) McGraw Hill Ryerson 2007

A shadow is created when an opaque object absorbs light rays. Shadows A shadow is created when an opaque object absorbs light rays. Shadows demonstrate that light travels in straight lines. A ray diagram shows how the distance from the light source affects the size of the shadow an object makes. See page 171 (c) McGraw Hill Ryerson 2007

Shadow sized depends on distance f rom light source (c) McGraw Hill Ryerson 2007

Shadows s (c) McGraw Hill Ryerson 2007

Check your understanding How is an opaque material different from a translucent material? How is a translucent material different from a transparent material? Is a glass of water with red food colouring in it translucent or transparent? What is the relationship between the size of the shadow and the distance of the object from the light source? (c) McGraw Hill Ryerson 2007

Reflection is when light bounces off of an object. Light Can Be Reflected 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. Reflected ray Incident ray Flat tin foil vs crumpled tin foil See page 172 (c) McGraw Hill Ryerson 2007

The normal is an imaginary line perpendicular to the surface. The Law of Reflection 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 reflection (r) equals the angle of incidence. (i) See page 173 (c) McGraw Hill Ryerson 2007

The angle of reflection (r) equals the angle of incidence (i). The Laws of Reflection The angle of reflection (r) equals the angle of incidence (i). The reflected ray and the incident ray are on opposite sides of the normal. The incident ray, the normal, and the reflected ray lie on the same plane (flat surface). See page 173 (c) McGraw Hill Ryerson 2007

Law of Reflection (c) McGraw Hill Ryerson 2007

Check your understanding What is the law of Reflection? Why does a white page not reflect like a mirror? What is the difference between the incident ray and the reflected ray? What point does the normal intersect? What does the angle of incidence always equal? (c) McGraw Hill Ryerson 2007

Activity 5-5 p178 (c) McGraw Hill Ryerson 2007

This change in speed causes the light to change direction. Light Can Be Refracted When light travels from one transparent medium to another of a different density, 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. See page 174 (c) McGraw Hill Ryerson 2007

Once inside the glass the light rays move in a straight line. Light Can Be Refracted When light rays move from air into glass, they slow down and change direction because the glass is denser than air. Once inside the glass the light rays move in a straight line. What will happen if the light rays leave the glass and move back into air, which is less dense? See page 174 (c) McGraw Hill Ryerson 2007

They will travel faster and change direction again (refract) Light Can Be Refracted They will travel faster and change direction again (refract) See page 174 (c) McGraw Hill Ryerson 2007

Light Can Be Refracted The angle of refraction is measured from the refracted ray to the normal. See page 174 (c) McGraw Hill Ryerson 2007

Refraction of Light in Water Objects in water appear in a different location than they actually are. This is due to the refraction of the light. See page 175 Take the Section 5.1 Quiz (c) McGraw Hill Ryerson 2007

Refraction of Light in Air Air at different temperatures has different densities. Warm air is less dense than cold air. Light refracts when it passes through air at different temperatures. (mirage) See page 175 Take the Section 5.1 Quiz (c) McGraw Hill Ryerson 2007

Refraction of Light in Air The “pools of water” you see on the highway on a hot day is due to the air closer to the ground is hotter and less dense than air higher up. Light from the sky directed at the ground is bent upward as it enters the less dense air. The “pools of water” are actually images of the sky refracted by warm air near the ground. See page 175 Take the Section 5.1 Quiz (c) McGraw Hill Ryerson 2007

Check your understanding Why does a white page not reflect like a mirror? What is the difference between the incident ray and the reflected ray? What point does the normal intersect? What does the angle of incidence always equal? What happens with light rays travel from water into air? Why do objects underwater seem closer to the surface than they are? Why does the highway ahead of you sometimes look wet when it is actually dry? (c) McGraw Hill Ryerson 2007

Homework Read pages 168-173 Answer CYU p181 # 1, 2, 3, 4, 6, 9 (c) McGraw Hill Ryerson 2007