THE ELECTROMAGNETIC SPECTRUM & LIGHT Chapter 18

 What types of waves are electromagnetic waves?

ELECTROMAGNETIC WAVES  Transverse waves consisting of changing electric fields and changing magnetic fields  Carry energy from place to place

HOW ARE THEY PRODUCED?  Produced by constantly changing fields  Electric Field  A region of space that exerts electrical forces on charged particles  Magnetic Field  A region of space that produces magnetic forces  Produced by magnets, by changing electric fields, and by vibrating charges

HOW THEY TRAVEL?  Changing electric fields produce changing magnetic fields and changing magnetic fields produce changing electric fields  They regenerate each other!  Electromagnetic Radiation  The transfer of energy by electromagnetic waves traveling through matter or across space

HOW THEY TRAVEL?  Do NOT require a medium to transport energy  Can travel through a vacuum, or empty space, OR through matter

CHECK POINT  On your white board, answer the following question:  Compared to the direction of wave movement, in what direction do the magnetic and electric fields of an electromagnetic wave vibrate?

HOW FAST IS LIGHT?  Thunder & Lightning example  Michelson’s Experiment Activity

SPEED OF LIGHT  In a vacuum (empty space) 3.0 x 10 8 meters per second

ELECTROMAGNETIC WAVES  Differ in wavelength and frequency  What is the relationship between wavelength and frequency?  Electromagnetic radiation behaves sometimes like a wave, and sometimes like a particle

LIKE A WAVE?  Young’s Experiment  Page 536 (Superposition of waves)

LIKE A PARTICLE?  Photoelectric Effect  The emission of electrons from a metal caused by a light striking the metal  Einstein proposed that light travels in packets of energy called PHOTONS  The amount of energy that a photon has is proportional to the frequency of the electromagnetic wave  Greater frequency = more energy

LIGHT WAVE INTENSITY  Similar to sound intensity  Light intensity is the same thing as brightness  Photons of light travel outward from a light source in all directions  The farther away from a light source an observer is, the less intense the light will be because it is spread out over a larger area

ELECTROMAGNETIC SPECTRUM PROJECT  PowerPoint Project

BEAD ACTIVITY  Figure out what they do/ don’t do, put them in order, take a phone picture, send an to Ms. Williams with your pic along with a description of what the beads do and why you think they do it!  Page 544 Sunscreen Activity

FLASHLIGHT ACTIVITY  Inrto to visible light activity

BEHAVIOR OF LIGHT 18.3

WARM-UP  List the parts of the electromagnetic spectrum in order of longest wavelength to shortest wavelength  Light behaves both like a wave and like a ______________.

COLOR

WHITE LIGHT  Made up of all the colors of the visible spectrum (ROY G BIV)  Prisms  As white light passes through a prism, shorter wavelengths refract more than longer wavelengths, and the colors separate (called dispersion)  Red bends the least (top of rainbow)  Violet bends the most (bottom of rainbow)

SEEING COLOR  Objects appear to be a certain color because they are reflecting that color of light and absorbing all the other colors  A red shirt reflects red light and absorbs all the other colors

PRIMARY COLORS OF LIGHT  Red, Green & Blue  When colors of light are mixed together, the colors add together to form a new color

WHAT IS A PIGMENT  A material that absorbs some colors of light and reflects others  Primary Colors of Pigment  Cyan, Magenta, & Yellow  Used in printers – can be combined to make any color!

SEEING LIGHT  The reason we are able to see objects is because light bounces off those objects, through matter, and then into our eyes  Light is not able to pass through all materials

TYPES OF MATERIALS Transparent Transmits light A material that allows light to pass through it Translucent A material that scatters light Objects viewed through this type of material do not look distinct Opaque A material that either absorbs or reflects all of the light that hits it Does not allow any light to pass through

REFLECTION  Why can you see yourself in a mirror?  Aluminum foil demonstration  Flat  Crumpled

REFLECTION Regular Reflection Diffuse Reflection  Parallel light waves strike a surface and reflect in the same direction  Light hits a smooth, polished surface, like a mirror  Parallel light waves strike a rough, uneven surface and reflect in many different directions

LAW OF REFLECTION  Assumes light travels in straight lines  When light strikes a surface it bounces off and can change directions  Law of Reflection  The angle of reflection is equal to the angle of incidence

TYPES OF MIRRORS Plane Mirror with a flat surface Produces a virtual image, or an exact copy of an object Convex The outside surface of a curved mirror is reflecting light Cause light rays to spread out Image is always upright and smaller than the actual object Concave The inside surface of a curved mirror is reflecting light Cause light rays to converge at a single point Uses: Vehicle headlights, produce a single bright beam of light

REFRACTION  A light wave bends (or refracts) when it passes at an angle from one medium into another  Causes Mirages  A false or distorted image (p 548)

SCATTERING  Light is redirected as it passes through a medium  The atmosphere contains molecules and small particles that scatter sunlight  Scattering causes deep red/ orange/ pink sunsets  Particles in the atmosphere cause the shorter wavelengths of visible light to scatter (like blue and green)  At sunrise and sunset light travels a greater distance to get to your eyes so it runs in to more particles  The light that remains for your eyes to perceive is made up of red and orange wavelengths

Why is the sky blue?

SCATTERING!  When the sun is high in the sky it travels a shorter distance to the observer  Particles and molecules in the atmosphere scatter blue light in all directions more so than any other color of light, so the sky appears blue  Air is COLORLESS!

EXIT QUESTION  What is the difference between reflection and refraction of light?  Respond in sentence or bullet points

WHAT IS A LENS?  An object made of transparent material that has one or two curved surfaces  Lenses refract (or bend light)  Depends on lens curvature and thickness

TYPES OF LENSES ConcaveConvex  Curved inward at the center  Cause light rays to spread out  Curved outward at the center  Cause light rays to come together at one point (called a focal point)

THE EYE Figure 17

NEARSIGHTED NESS Figure 18

NEARSIGHTED NESS Figure 18

FARSIGHTEDNESS Figure 19

FARSIGHTEDNESS Figure 19

FINDING YOUR BLIND SPOT  Take an index card, make an X on the card about 3-4 cm from the right hand edge. Next draw a dot 5-6 cm to the left of the X.  Cover your right eye, stare at the X with your left eye. Slowly move the card closer to your eye until the dot disappears. Have your partner use a meter stick to measure the distance from your eye to the index card.