# Energy to See By 1.  Alien Attack Website: alienattack.htm 2.

## Presentation on theme: "Energy to See By 1.  Alien Attack Website: alienattack.htm 2."— Presentation transcript:

Energy to See By 1

 Alien Attack Website: http://www.engineeringinteract.org/resources/ alienattack.htm 2

 Light must come from a light source.  A light source is something that produces light.  The sun and a burning candle are light sources. 3

 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? 4

 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. 5

 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. 6

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. 7

 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 8

 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. 9

 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. 10

 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/speed 3. Replace distance and speed with the values given: time = 384,000km/300,000km/s time = 1.28 s 11

 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 12

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 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. 14

 the bouncing back of a wave (of light, sound, or heat) when the wave hits a surface that it does not go through 15

 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. 16

 When light hits a very smooth surface, the light is reflected at equal angles.  This is called regular reflection. 17

 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. 18

Angle of incidence = angle of reflection 19

 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? 20

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