energy to see by 1. alien attack website: alienattack.htm 2

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LightEnergy to See By

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Introduction to Light

Alien Attack Website:http://www.engineeringinteract.org/resources/alienattack.htm

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Light Rays and Sources

Light must come from a light source.

A light source is something that produces light.

The sun and a burning candle are light sources.

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Light Rays and Sources

Light travels in a straight line.

We use arrows to show light rays that are produced by light sources.

Black Box Experiment What do you see in

the box? Why?

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Shadows

Shadows occur when an object blocks light from a light source.

The size of the shadow changes depending on where the object and light source are placed.

More light is blocked when the object is near the light source. This makes a bigger shadow.

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Opaque, Transparent or Translucent

An object that does not allow light through is called opaque.

Objects or substances that allow all, or nearly all, light through them are called transparent.

Objects that allow some light to pass through them are called translucent.

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Opaque, Transparent or Translucent

A translucent material transmits light, but unlike a transparent material, it also scatters the light so those objects behind the material cannot be seen clearly.

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What Is Light?

Light is a type of energy that travels as a wave.

Light does not require matter to travel through.

Light travels in the form of electromagnetic waves.

Electromagnetic wave: a wave that consists of electric and magnetic fields that vibrate at right angles to each other

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What Is Light?

Some properties of light can be explained only by using a particle model of light.

Light is thought of as a stream of particles called photons.

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The Speed of Light

In the near vacuum of space, the speed of light is about 300,000,000 m/s or 300,000 km/s.

It take about 8.3 minutes for light to travel from the sun to Earth, because the Earth is 150,000,000km from the sun.

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The Speed of Light

The distance from Earth to the moon is 384,000 km. Calculate the time it takes for light to travel that distance.

1. Write the equation for speed:speed = distance/time

2. Rearrange the equation by multiplying by time and dividing by speed

time = distance/speed3. Replace distance and speed with the values

given: time = 384,000km/300,000km/stime = 1.28 s

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The Speed of Light

Now It’s Your Turn

The distance from the sun to Venus is 108,000,000km. Calculate the time it takes for light to travel that distance.

Answer: Time = 360 s

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Interactions of Light Waves and Matter

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Interactions of Light Waves and Matter

When light strikes any form of matter, it can interact with the matter in three ways:

It can be reflected.It can be absorbed.It can be transmitted.Or most likely, some combination of these happens.

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Reflection

the bouncing back of a wave (of light, sound, or heat) when the wave hits a surface that it does not go through

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Reflection

When light rays hit objects they may bounce off or be reflected.

If the surface is rough they bounce off in many directions.

We see things when the reflected light travels into our eyes.

Bright shiny objects reflect more light than dark, dull ones.

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Reflection

When light hits a very smooth surface, the light is reflected at equal angles.

This is called regular reflection.

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Reflection

The normal line is at a right angle to the mirror.

The angles of incidence and reflection are measured from the ray to the normal.

What can you say about angle i and angle r in figure 1?

Angle i = Angle r

Incidence is the arrival of a beam of light at a surface.

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Law of Reflection

 Angle of incidence = angle of reflection 

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Reflection

Objects that produce visible light are called luminous.

A visible object that is not a light source is illuminated.

Is the object to the right luminous or illuminated?