Scimatics 8H

Behaviour of Light

Ray model of light can be used to understand how light moves in straight lines, reflects off mirrors, and refracts through lenses. A ray is an arrow that is used to show the direction of the straight-line path of light. We can use ray diagrams to study and predict how light behaves.

What evidence have you experienced that proves light travels in straight lines?

Light and MatterOne use for the ray model is to help in understanding what happens when light energy reaches different materials. The type of matter in an object determines the amount of light it absorbs, reflects, refracts, and transmits,

Transparent material allows light to pass through it freely. Only a small

amount of light is absorbed and reflected.o Examples include:

Translucent material, such as frosted glass or a lampshade, most light rays get through, but are scattered in all directions.

o Examples include:

Opaque material prevents any light from passing through it

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Opaque(blocked)

Translucent(scattered)

Transparent

Scimatics 8Ho Examples include:

Light can be reflected, absorbed, transmitted, or refracted

Reflection: Reflection occurs when a light wave strikes an object and bounces off.

Example: When sunlight strikes coloured clothing, some colours are reflected while other colours are absorbed. Only the reflected colours can be seen. An object looks blue in sunlight because it reflects blue and absorbs colours other than blue from the sunlight.

The Law of ReflectionLight is reflected in a specific manner, following the

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Scimatics 8H

Law of Reflection.

Incident ray is the incoming ray. The ray of light that bounces off the

surface/barrier is the reflected ray. The normal is an imaginary line that is

perpendicular to the boundary between two materials (such as air and glass) and intersects the point at which the incident ray reaches the boundary.

Absorption: Light energy becomes trapped in an object as heat.

Transmission: Light energy that passes through a medium and keeps travelling

Refraction: What happens when a light wave passes from one material to another?

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Normal

Scimatics 8HIf a light wave is travelling at an angle and the speed that light travels is different in the two materials, the wave will be bent, or refracted. Refraction is the bending or changing direction of a wave as it passes from one material to another.

1. Medium - A substance that makes possible the transfer of energy from one location to another, especially through waves. Examples – Water and Air

2. Normal Line – an imaginary line drawn perpendicular (900) to a surface hit by a ray of light. (Represented by a dotted in line below)

Phet Simulation of Refraction- In Class1. Draw what happens to the light ray when it travels through AIR then into

WATER.Prediction Observation

Air Air

Water Water

2. Light rays change speed when they strike particles of matter. We know that water is denser than air. When light passes from air into water the speed of light decreases. Using the Particle Model of Matter provide an explanation for why light slows down as it passes from air to water.

3. As light travels from a less dense medium to a more dense medium the light wave encounter more and more particles which act to slow down the speed of the light in the medium with a greater density.

4. When light slows down does it refract, (bend) towards the NORMAL or refract, (bend) away from the NORMAL.

5. Draw what happens to the light ray when above and below the line are both WATER.

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Scimatics 8HPrediction Observation

Water Water

Water Water

6. Why does the light in this example not refracted? Provide an explanation.

7. Draw what happens to the light ray when above and below the line are both AIR.

Prediction ObservationAir Air

Air Air

8. Was the above result expected? Explain

9. Change the top material to Air and the bottom material to Mystery A. Draw what happens to the light ray.

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Scimatics 8HObservation

Air

Mystery A

10. Do you think Mystery A could be AIR? Why or Why not?

11. Do you think the density of Mystery A is greater or less than the density of water? Explain your answer. (Hint: you might want to use the protractor).

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