# 5.3 - Light

The student will investigate and understand basic characteristics of visible light and how it behaves. Key concepts include

a)  transverse waves;

• diagram and label a representation of a light wave, including wavelength, crest, and trough  Bloom;s Level:  Remember

b)  the visible spectrum;

• explain the relationships between wavelength and the color of light   Bloom;s Level: Understand/ Apply
• name the colors of the visible spectrum  Bloom;s Level: Remember

c)  opaque, transparent, and translucent;

• explain the terms transparent, translucent, and opaque   Bloom;s Level:  Understand
• give examples of each   Bloom;s Level: Understand

d)  reflection of light from reflective surfaces; and

•  compare and contrast reflection and refraction, using water, prisms, and mirrors  Bloom;s Level:  Analyze

e)  refraction of light through water and prisms.

• compare and contrast reflection and refraction, using  water, prisms, and mirrors  Bloom;s Level:  Analyze
• analyze the effects of a prism on white light   Bloom;s Level: Analyze
• describe why a prism refracts light  Bloom;s Level: Understand
• explain the relationship between the refraction of light and the formation of a rainbow  Bloom;s Level: Understand/Analyze

### BIG IDEAS

Light is a form of energy that has certain properties.

### UNDERSTANDING THE STANDARD

• Light has properties of both a wave and a particle. Recent theory identifies light as a small particle, called a photon. A photon moves in a straight line. In both the light wave and photon descriptions, light is energy.
• Because light has both electric and magnetic fields, it is referred to as electromagnetic radiation. Light waves move as transverse waves and travel through a vacuum at a speed of approximately 186,000 miles per second (2.99 x 108 meters per second). Compared to sound, light travels extremely fast. It takes light from the sun less than 8½ minutes to travel 93 million miles (150 million kilometers) to reach Earth.
• Unlike sound, light waves travel in straight paths called rays and do not need a medium through which to move. A ray is the straight line that represents the path of light. A beam is a group of parallel rays.
• Light waves are characterized by their wavelengths and the frequency of their wavelengths
• The size of a wave is measured as its wavelength, which is the distance between any two corresponding points on successive waves, usually crest-to-crest or trough-to-trough. The wavelength can be measured from any point on a wave as long as it is measured to the same point on the next wave.
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• Frequency is the number of waves passing a given point every second. The greater the frequency, the greater the amount of energy.
• Light waves are waves of energy. The amount of energy in a light wave is proportionally related to its frequency: high frequency light has high energy; low frequency light has low energy. The more wavelengths in a light wave in a given period of time, the higher the energy level. Thus gamma rays have the most energy, and radio waves have the least. Of visible light, violet has the most energy and red the least.
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• The entire range of electromagnetic radiation (light) is called the electromagnetic spectrum.
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• The only difference between the various types of electromagnetic radiation is the amount of energy. Sunlight consists of the entire electromagnetic spectrum.
• The wavelengths detectible by the human eye represent only a very small part of the total electromagnetic spectrum.
• We see visible light as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. The colors of the visible spectrum from the longest wavelength to the shortest wavelength are: red, orange, yellow, green, blue, and violet (ROYGBV). Most scientists no longer include the color indigo, which used to be included between blue and violet.
• Black and white are not spectral colors. Black is when a material absorbs all the visible light and no light is reflected back. Black is a total absence of reflected light. White is a reflection of all visible light together.
• Light travels in straight paths until it hits an object, where it bounces off (is reflected), is bent (is refracted), passes through the object (is transmitted), or is absorbed as heat.
• The term reflected light refers to light waves that are neither transmitted nor absorbed, but are thrown back from the surface of the medium they encounter. If the surface of the medium contacted by the wave is smooth and polished (e.g., a mirror), each reflected wave will be reflected back at the same angle as the incident wave. The wave that strikes the surface of the medium (e.g., a mirror) is called the incident wave, and the one that bounces back is called the reflected wave.
• Refraction means the bending of a wave resulting from a change in its velocity (speed) as it moves from one medium to another (e.g., light moving from the air into water). The frequency of the wave does not change.
• The amount of bending of the light wave (refraction) depends on:
1. The density of the material it is entering;
2. The wavelength of the light wave; and
3. The angle at which the original light wave enters the new medium.
• Some examples of refraction are when:
1. Refraction causes a setting sun to look flat.
2. A spoon appears to bend when it is immersed in a cup of water. The bending seems to take place at the surface of the water, or exactly at the point where there is a change of density.
3. Shadows on the bottom of a pool are caused because air and water have different densities.
4. A glass prism disperses white light into its individual colors. As visible light exits the prism, it is refracted and separated into a display of colors.
• A rainbow is an example of both refraction and reflection. Sunlight is first refracted when it enters the surface of a spherical raindrop, it is then reflected off the back of the raindrop, and once again refracted as it leaves the raindrop.
• A prism can be used to refract and disperse visible light. When the different wavelengths of light in visible light pass through a prism, they are bent at different angles (refracted). Dispersion occurs when we see the light separated into a display of colors: ROYGBV.
• Dispersion is the separation of light. Dispersion occurs with transparent surfaces that are not parallel to each other, such as a prism or gemstone facets.
• Light passes through some materials easily (transparent materials), through some materials partially (translucent materials), and through some not at all (opaque materials). The relative terms transparent, translucent, and opaque indicate the amount of light that passes through an object.
1. Examples of transparent materials include clear glass, clear plastic food wrap, clean water, and air.
2. Examples of translucent materials include wax paper, frosted glass, thin fabrics, some plastics, and thin paper.
3. Examples of opaque materials include metal, wood, bricks, aluminum foil, and thick paper.

### ESSENTIALS

Essential Questions:

·  How do scientists describe and measure the properties of light?

·  How does the behavior of light affect our everyday lives?

·  What are the pros and cons of using artificial light versus natural light?

·  How would you use opaque, translucent, and transparent materials to design a living environment?

·  How are reflection and refraction similar and different?

·  How does a prism affect white light?

·  How is a rainbow formed?

In order to meet this standard, it is expected that students will

• diagram and label a representation of a light wave, including wavelength, crest, and trough.
• explain the relationships between wavelength and the color of light. Name the colors of the visible spectrum.
• explain the terms transparent, translucent, and opaque, and give an example of each.
• compare and contrast reflection and refraction, using water, prisms, and mirrors.
• analyze the effects of a prism on white light and describe why this occurs.
• explain the relationship between the refraction of light and the formation of a rainbow.

### KEY VOCABULARY

absorbed - to take in; light rays are absorbed as heat

color - spectral colors include red, orange, yellow, green, blue and violet; black is the absence of reflected light and white is a reflection of all the visible light

crest - top part of a wave

electromagnetic spectrum - the entire range of wavelengths or frequencies of electromagnetic radiation (light) extending from gamma rays to the longest radio waves and including visible light

energy - light waves are waves of energy; the higher the frequency of a light ray the more energy or power it possesses; gamma rays have the most energy and radio waves the least amount of energy

frequency - the number of waves passing a given point every second; the greater the frequency,  the greater the amount of energy

medium -  light does NOT need solids, liquids or gases to be transmitted

mirror - a flat, polished surface which reflects light

opaque - materials which do not allow light to pass through; examples include metal, wood, aluminum foil, cardboard and bricks

prism - used to refract and disperse visible light

ray - the straight line that represents the path of light

reflection - the bouncing back of light rays

refraction - the bending of light rays

ROYGBV - the colors of the longest wavelength to the shortest wavelength; red, orange, yellow, green blue and violet; red has the longest wavelength and violet the shortest

translucent - materials which allow some light to pass through but not all; examples include frosted glass, wax paper, thin paper and fabrics and some plastics

transmitted

transparent - materials which allow light to easily pass through; examples include clear glass, water, air, plastic wrap

transverse wave - method by which light rays travel

trough - the bottom of a transverse wave

visible light - the small part of the electromagnetic spectrum detected by the human eye

wavelength - the distance between any two corresponding points on successive waves; usually crest to crest or trough to trough; it can be measured from any point on a wave as long as it is measured to the same point on the next wave.

white light - contains all the wavelengths of the visible spectrum with equal intensity

Updated: May 20, 2016