Chapter 9. Properties of Light Waves

Learning Objectives

amplitude
the height of a light wave, measured as the distance between the peak and the midpoint; related to the brightness of a light
hue
the apparent color of the light; related to wavelength
brightness
the apparent intensity of the light; related to amplitude
wavelength
the width of a light wave, measured as the distance between peaks; related to the hue (perceived color) of a light
Properties of Light Waves
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A colored bar runs vertically on the left side of the image. The bar transitions from violet at the top to dark red at the bottom. Each color in the bar has waves extending to the right representing the light waves for that color. The nanometers of the light waves increases from 400 nanometers for violet at the top of the bar to 700 nanometers for dark red at the bottom of the bar. As the nanometers increases, the light waves get wider. The following table lists the nanometers associated with each color in the figure: 400 nanometers, color - violet; 425 nanometers, color - indigo; 470 nanometers, color - blue; 490 nanometers, color - aqua; 550 nanometers, color - green; 600 nanometers, color - yellow; 630 nanometers, color - orange; 665 nanometers, color - red; 700 nanometers, color - dark red;
Learning Objectives:

Describe the two main characteristics of light waves.

Explain how the two main characteristics of light waves influence our perception of light.

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The figure is a diagram of the eye from the side. In front of the eye is an ice cream cone. Dotted lines show light waves reflecting off the ice cream cone and going inside the eye. The light waves end at the back of the eye. At the back of the eye there is a picture of an upside down ice cream cone.

1. We see the world around us because the objects in our environment reflect light energy into our eyes.

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2. This light energy comes in the form of waves that have two main properties, or characteristics: wavelength and amplitude. Changes in these properties produce changes in what we see.

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There are two images, one above the other. The top image is a series of four light waves running horizontally. A horizontal line runs through the middle of the waves. The distance between the top of the first wave and the top of the second wave is identified with a horizontal dotted line labeled Wavelength. The bottom image is a series of four light waves running horizontally. A horizontal line runs through the middle of the waves. The distance between the top of the first wave and the horizontal line is identified with a vertical dotted line labeled Amplitude.

3. Wavelength is the distance between peaks in a wave. Amplitude is the height of the wave, sometimes measured from peak to trough (lowest point), but more often measured from the midpoint to the peak.

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There are two images. The first image is a graph titled Wavelength and hue. The X axis ranges from 400 nanometers to 700 nanometers in increments of 100. The area before 400 nanometers is labeled ultraviolet. The area after 700 nanometers is labeled infrared. The area of the graph is colored so that it transitions from violet on the left at 400 nanometers to dark red on the right at 700 nanometers. The color of the area transitions from violet to blue to green to yellow to orange to dark red. Over the colored area is a light wave drawn using a line. The waves start off skinny and close to each other at 400 nanometers and get wider and more spread out at 700 nanometers. As we move from left to right in the graph the distance between the peaks gets wider, thus the nanometers increases. The second image is a graph titled Amplitude and brightness. The area of the graph is colored red but transitions from very dark red, almost black, on the left to very light red, almost white, on the right. Over the colored area is a light wave drawn using a line. The waves start out very short, almost flat, on the left to very tall on the right. As the waves get taller or the amplitude increases, the color becomes brighter.

4. Wavelength determines the hue, or color experience. Short-wavelength light is violet or blue, while long-wavelength light is red. Amplitude determines the brightness of the light. Low-amplitude light is dim or dark, while high-amplitude light is bright.

Practice 1: Wavelength

wavelength
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Practice 1: Wavelength

Use the slider to vary the wavelength, and then observe the change in the beam of light.

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Bluish hue
Greenish hue
Reddish hue
Short Medium Long
Wavelength

Wavelength is the distance between peaks in a wave. Wavelength determines the hue, or color sensation. Short-wavelength light appears violet or blue, while long-wavelength light appears orange or red.

Practice 2: Amplitude

amplitude
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Practice 2: Amplitude

Use the slider to vary the amplitude of the wave, and then observe the change in the beam of light.

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dim, dusky color
brighter color
intense bright color
Low Medium High
Amplitude

Amplitude is the height of the wave. Amplitude determines the intensity, or brightness, of the light. The higher the amplitude, the brighter the light.

Quiz

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Quiz

Match the terms to the descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

Perhaps you should go back to review the properties of light waves.
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hue
wavelength
brightness
amplitude
Determined by amplitude (intensity) of light waves.
Determined by wavelength of light waves.
Line Drawing: measurement of light waves (several) in terms of “wavelength”
Line Drawing: measurement of light waves (several) in terms of “amplitude”

Conclusion

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