Section 2.1-2.2Pages 188-196

Light Travels in Rays and Interacts with MaterialsSection 2.1 – pages 188-193Learner Outcome

I can investigate how light is reflected, transmitted and absorbed by different materials; and describe differences in the optical properties of various materials

Light InteractionDepending on the

situation, light will reflect, absorb and transmit at or through objects.

Remember that light travels in straight lines from objects to your eyes.

Ray DiagramsRay diagrams are

used to show how light travels.

Light traveling from a source is shown as a straight line called a ray.

Ray diagrams can help explain why the brightness or intensity of light changes with distance.

Ray diagrams also help to explain shadows. A lack of light is considered to be a shadow.

Ray Diagrams Light hits an object and is reflected to the eye thereby producing an image of the object.

Look on page 190 to see a light rays moving to your eyes and light casting shadows.

Light Interacts With Materials

When light hits an object, it behaves in different ways depending on they type of the material each object is made of.

Transparent materials can transmit light – it passes right through them.

Eg. Glass, clear plastic

From air into water or glass

Other types of materials that light comes into contact withTranslucent – allow some,

but not all, light to pass through. Eg. Frosted window pane.

Opaque – do not let any light through. They absorb or reflect the light. Shadows are created as light passes in front of these materials. Eg. Brick, wood, metal.

Other Types of MaterialsNon-Luminous –

they do not produce light. Also includes opaque objects.

Luminous – a light source. Eg. Lamp, the sun, fire.

Types of Reflection: Regular Reflection Regular

Reflection – light rays hit a smooth surface.

Light rays are parallel to each other.

Reflected at same angle.

Produce clear image.

Types of Reflection:Diffuse Reflection Diffuse Reflection –

when light rays strike a rough or uneven surface.

Reflected at a different angle.

Rays do not remain parallel.

Scatter the light rays.

Can see objects from many positions.

Sample Example QuestionShadows can be created when;a. Light bends around an object.b. Black light is shone onto an object.c. When light hits and opaque object.d. When light strikes an object and

projects black light.

Did you…… investigate how light is reflected, transmitted and absorbed by different materials; and describe differences in the optical properties of various materials?

Check and Reflect Questions#’s 1-5, page 1931. Explain how you could change the direction

of a ray of light. Include a diagram in your answer.

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Check and Reflect Questions#’s 1-5, page 1932. A basketball does not give off light. Explain,

with the help of a ray diagram, how you are able to see a basketball.

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Check and Reflect Questions#’s 1-5, page 1933. What happens to light when it hits a

translucent object? Explain your answer.________________________________________________

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4. Which would make a better reflector, a piece of metal or a piece of wood? Explain why?

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Check and Reflect Questions#’s 1-5, page 1935. Explain with the help of ray diagrams, why

the shadow created by your hand on a wall grows bigger when you move your hand toward the light source.

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The Law of ReflectionLearner Outcome

I can measure and predict angles of reflection

The Law of ReflectionIncident Rays – are the incoming rays

of light.

The shinier and smoother the surface the better the reflection.

Plane Mirrors – flat mirrors – will allow for the clearest of reflections

How are two way mirrors constructed? (pg 194 left side panel)

The Law of ReflectionWhen a ray of light hits a plane mirror at

an angle, it bounces off the mirror surface at exactly the same angle.

The “Normal” – a line perpendicular to the mirror at the point of reflection

Angle of incidence – the angle between the incident ray and the normal

Angle of reflection – the angle between the reflected ray and the normal.

The Law of Reflection cont…THE LAW OF

REFLECTION – the angle of incidence is equal to the angle of reflection.

Reflection Assignment Sheet:Complete the following questions on your own.Calculate the following angles/amounts:Q1: What is the angle of reflection of a ray coming directly

down the NORMAL to the mirror?_________________

Q2: If the angle of reflection is 39 degrees, what is the angle of incidence? _______________

Q3: If the angle of incidence between the ray and the NORMAL is 40 degrees, what is the angle of reflection between the ray and the mirror? ______________

Q4: A ray that reflects off a mirror has an angle of 30 degrees between it and the mirror. What is the sum of the angle of incidence and reflection when measured against the NORMAL? ______________

Q5: If 10 rays of light and 10 rays of gamma radiation encounter a normal mirror at the incidence, how many rays will get reflected? ___________

/5

Sample Exam QuestionA line drawn perpendicular to a

mirror at the point of reflection is said to be;

a. Normalb. Reflectedc. Incidentd. Refracted

Did you…… measure and predict angles of reflection?

Check and Reflect Questions#’s 1-4, page 196

1. If you see someone in a mirror, can they see you? Explain why or why not? Use a ray diagram to help answer this question.

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2. Why do you think mirrors are so useful in magic acts?

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Check and Reflect Questions#’s 1-4, page 1963. Draw a “view from above” ray diagram that

illustrates an arrangement of mirrors that would allow you to see the back of your head while looking straight ahead. How can you direct this light ray to your eyes? Mark the angles of incidence and reflection on your diagram.

Check and Reflect Questions#’s 1-4, page 1964. With diffuse reflection, do you think light

rays obey the law of reflection? Why or why not? Explain your answer.

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