Table of Contents The Nature of Electromagnetic Waves Waves of the Electromagnetic Spectrum Light and Color Reflection and Mirrors Refraction and Lenses Electromagnetic Waves and Light

The Electromagnetic Spectrum

What makes up an electromagnetic wave? An electromagnetic wave is a transverse wave that involves the transfer of electric and magnetic energy. It is made up of vibrating electric and magnetic fields that move through space or some medium at the speed of light.

Electromagnetic Wave An electromagnetic wave travels through space at the speed of light— about 300,000 kilometers per second. The Nature of Electromagnetic Waves

What models explain how electromagnetic waves behave? Is light a particle or a wave? Wave Model of Light: An ordinary beam of light consists of waves that vibrate in all directions. A polarizing filter acts as though it has tiny slits aligned in only one direction, either horizontal or vertical, allowing only some waves to pass through. The light that passes through is called polarized light. Simple Explanation of Polarised Lenses

Light as a Wave A polarizing filter acts like the slits in a fence. The Nature of Electromagnetic Waves

Particle Model of Light: When a beam of high frequency light shines on some metals, electrons move. Sometimes it moves so much that it is knocked out of the metal and is called the photoelectric effect. Light can be thought of as tiny a particle of energy called a photon, that contains enough energy to knock an electron free from the metal. A Level Physics - The Photon

The Photoelectric Effect Photons hitting a metal surface knock out electrons. The Nature of Electromagnetic Waves

Electromagnetism : Documentary on How the Electromagnetic Spectrum Works (Full Documentary)

How do electromagnetic waves compare? All electromagnetic waves travel at the same speed in a vacuum. A vacuum is space without any gas. They have different wavelengths and different frequencies.

Visible light is the only light we can see. As wavelength decreases, the frequency increases, so waves with the shortest wavelengths have the highest frequencies. The higher the frequency of a wave, the higher its energy. Complete pg 405

Comparing Electromagnetic Waves Different types of electromagnetic waves have different wavelengths. Which are the visible light, radio waves, and X- rays? Waves of the Electromagnetic Spectrum

What makes up the EM spectrum? Radio Waves: EM waves with the longest wavelengths and lowest frequencies are radio waves. Radio waves are used to carry signals at certain frequencies. Complete pg 406

Waves of the Electromagnetic Spectrum The Electromagnetic Spectrum The electromagnetic spectrum can be broken up into different categories. Use the word bank to complete the boxes in the diagram.

Microwaves: Microwaves have a higher frequency than radio waves. Besides heating up food, microwaves are useful in radar and cellular phones. Radar (radio detecting and ranging) uses reflected microwaves to detect objects. Distance: by measuring the time it takes for the signal to return, the distance between objects can be determined. Speed: by using the Doppler effect, the change in the frequency of the reflective waves from the original waves determines the speed of the moving object. Complete pg 407

Infrared Rays: Infrared rays have higher frequencies than microwaves, so have more energy. The invisible heat that we feel is infrared radiation or rays. Heat lamps have bulbs that give off mainly infrared rays. Warmer objects give off infrared rays with more energy and higher frequencies than cooler objects. A thermogram is an image that shows different temperatures with different colors. Complete pg 408

Visible Light: Visible light are the only waves we can see with our eyes and make up only a small part of the EM spectrum. The white light is actually a mixture of many colors based on their wavelengths. Ultraviolet Light: Since ultraviolet rays have higher frequencies than visible light, they carry more energy. Too much UV can damage cells, especially skin cells, but small doses are useful for skin to produce vitamin D. Complete pg 409

X-rays: Because of their high frequencies, X-rays carry more energy than UV rays and can penetrate most matter. Dense matter absorb X-rays, so they do not pass through. X-rays are useful in seeing cracks in dense material such as bone, teeth, steel, or concrete. Too much exposure to X-rays can be harmful. Gamma rays: Since they have the greatest amount of energy, gamma rays are the most penetrating of EM waves. Gamma rays are helpful in examining the body’s internal structures. Some radioactive substances and certain nuclear reactions produce gamma rays. Complete pg

Types of Waves The electromagnetic spectrum includes many kinds of waves. Identify each kind of wave on the electromagnetic spectrum. What is the name of the highest energy waves? Waves of the Electromagnetic Spectrum

What determines color? When light strikes an object, the light can be reflected, transmitted, or absorbed. Most materials can be classified as transparent, translucent, or opaque based on what happens to light that strikes the material.

Light can pass through a transparent material without being scattered, so you can see clearly what is on the other side. A translucent material scatters the light that passes through it, so you can see an object, but the details are blurred. A material that reflects or absorbs all of the light that strikes it is called opaque, so you cannot see through it because light cannot pass through it. Complete pg 413

Types of Materials Suppose the ball was placed behind the three-sectional window below. Then, what would you see inside the dashed circle? Light and Color

Opaque objects: The color of an opaque object depends on the wavelengths of light that the object reflects. Every opaque object absorbs some wavelengths of light and reflects others. Transparent & translucent objects: Materials that are transparent or translucent allow only certain colors of light to pass through them. They reflect or absorb the other colors. A color filter allows only certain wavelengths to pass through, allowing only certain color of light to pass through. Complete pg

Color of an Opaque Object The color an apple appears to be depends on the color of the light that strikes it. Light and Color

Color Filters Imagine looking at the beach ball through a red, green, or blue filter. How will each section of the beach ball appear? Light and Color

How do colors combine? Primary colors of light are red, green, and blue (not the same as primary colors in art). When the three colors of light are combined in equal amounts, they produce white light. If colors are combined in unequal amounts, they produce a secondary color, such as yellow, cyan, or magenta. Any two colors (a secondary and primary) that combine to form white light are called complementary colors. Complete pg 416

Primary Colors of Light The primary colors of light are red, green, and blue. Combined in different amounts, the primary colors can produce other colors. Light and Color

Artists use pigments to absorb some colors and reflect others to produce shades of colors. As pigments are added together, fewer colors of light are reflected and more are absorbed. The more pigments that are combined, the darker the mixture looks. Cyan, yellow, and magenta (Ever wonder why these 3 colors are used in printer ink?) are the primary colors of pigments. When these 3 colors are combined, black is produced. Complete pg 417

Primary Colors of Pigment When the three primary colors of pigments are combined in equal amounts, they produce black. Light and Color

What are the kinds of reflection? To show how light reflects, you can represent light waves as straight lines called rays. Light obeys the law of reflection- the angle of reflection equals the angle of incidence.

Regular Reflection Regular reflection occurs when parallel rays of light hit a smooth surface. All of the light rays reflect at the same angle so you see a clear image. Shiny surfaces produce regular reflection.

Diffuse Reflection Diffuse reflection occurs when parallel rays of light hit an uneven surface. Each light ray obeys the law of reflection but hits the surface at a different angle so each ray reflects at a different angle. You either don’t see an image or the image is not clear because the surface is not smooth. Even if it looks smooth, there are small bumps that reflect light at different angles. Complete pg 419

Diffuse and Regular Reflection Which kind of reflection occurs on each surface? Reflection and Mirrors

What types of images do mirrors produce? Plane Mirror: A plane mirror is a flat sheet of glass that has a smooth, silver-colored coating on one side. When light strikes a mirror, the coating reflects the light creating a virtual image. The image is virtual since it appears to be behind the mirror, but it really isn’t there. The image is not quite the same as the object since the left and right are reversed. A plane mirror produces a virtual image that is upright and the same size as the object.

Concave Mirror A mirror with a surface that curves inward, like a bowl, is a concave mirror. Rays of light are parallel to the optical axis, an imaginary line that divides the mirror in half. Concave mirrors reflect the parallel rays of light so that they meet at a point, called the focal point.

Concave Mirror A concave mirror reflects rays of light parallel to the optical axis back through the focal point. Reflection and Mirrors

Concave Mirrors The type of image that is formed depends on the location of the object. If the object is farther away from the mirror than the focal point, the reflected rays form a real image. A real image can be projected on a surface but it is upside down although it can be smaller, larger, or the same size as the object. If the object is between the mirror and the focal point, the reflected rays form a virtual image that is larger than the object. Concave mirrors produce magnified images. Complete pg 421

Real and Virtual Images The figures show how a concave mirror can produce both real and virtual images. Reflection and Mirrors

Convex Mirrors A mirror with a surface that curves outward is called a convex mirror. The reflected rays spread out the parallel rays of light but appear to come from a focal point behind the mirror. A convex mirror produces a virtual image that is always smaller than the object. Convex mirrors are used in cars to allow you to see a larger area that you could with a plane mirror, but the image is reduced in size and appears to be farther away than it really is. Complete pg 422

Convex Mirror Light rays parallel to the optical axis reflect as if they came from the focal point behind a convex mirror. Where do two reflected rays intersect behind the mirror? Reflection and Mirrors

Different Types of Images Formed by Mirrors Reflection and Mirrors Complete pg 423

What causes light to bend? Refraction can cause you to see something that may not actually be there. Light will bend each time it passes through a different medium such as water, glass, and air. When light rays eneter a new medium at an angle, the change is speed causes the rays to bend. Complete pg 425

Optical Illusion In a Fish Tank There is only one fish in the tank, but refraction makes it look as though there are two. Refraction and Lenses

Refraction in different mediums Some mediums cause light to bend more than others. Light travels fastest in air and slows as it passes through other mediums. Glass causes light to bend more than either air or water does so it has a higher index of refraction, the measurement of how much a light ray bends when it enters than medium.

Refraction of Light The light ray bends as it passes through different mediums. Refraction and Lenses

Bending Light The table shows the index of refraction of some common mediums. Refraction and Lenses Complete pg 426

Prisms and rainbows When white light enters a prism, each wavelength is refracted by a different amount causing white light to spread out into the colors of the spectrum. The same process occurs in water droplets suspended in the air. These water droplets act like tiny prisms and create a rainbow. Complete pg 427

Refraction and Lenses Rainbow A rainbow forms when light is reflected and refracted by water droplets suspended in the air.

Mirages Mirage is an image of a distant object caused by refraction of light. The puddles are light rays from the sky that are refracted to your eyes. The air just above the land is hotter than the air higher up. Light travels faster in hot air, and the light from an object traveling towards the ground are bent upward by the hot air. Our brain assumes that these rays traveled in a straight line so they look like they reflected off of a smooth surface. Complete pg 428

What determines the type of image formed by a lens? A lens is a curved piece of glass that refracts light and forms an images by refracting light rays that pass through it. A concave lens is thinner in the center. Light rays bend away from the optical axis and never meet creating only virtual images that are upright and smaller than the object.

Refraction and Lenses Concave Lens A concave lens produces a virtual image that is upright and smaller than the object. In the second diagram, where would the image be when the two light rays are extended back to the same side of the lens as the object?

A convex lens is thicker at the center. Light rays bend towards the center of the lens. The more curved the lens, the more it refracts light. When an object is between the lends and the focal point, the refracted rays form a virtual image on the same side of the lens and is larger than the object. When the object is outside of the focal point, the refracted rays form an upside down, real image on the other side of the lens that can be smaller, larger, or same size.

Refraction and Lenses How a Convex Lens Works The type of image formed by a convex lens depends on the object’s position. Which image is virtual and which is real? Complete pg 431

Lenses and Mirrors These photos show parallel rays of light passing through a convex lens and a concave lens. How would you complete the Lenses and Mirrors table? Refraction and Lenses

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