ultraviolet light

Light with wavelengths shorter than visible light is called ultraviolet light. The term ultraviolet means above violet. Ultraviolet light is the range of light waves that have shorter wavelengths and higher frequencies than violet light in the visible range of light. With higher frequencies than visible light, ultraviolet light has more energy. It can be used to kill bacteria in food and to sterilize surgical instruments. The human skin also makes vitamin D when it is exposed to ultraviolet light. Vitamin D, in turn, is needed for strong bones and teeth. Too much exposure to ultraviolet light can cause sunburn and skin cancer. As the slip, slop, slap slogan suggests, you can protect your skin from ultraviolet light by wearing clothing that covers your skin, applying sunscreen to any exposed areas, and wearing a hat to protect your head from exposure. The SPF, or sun-protection factor, of sunscreen gives a rough idea of how long it protects the skin from sunburn (see Figure 1.3). A sunscreen with a higher SPF value protects the skin longer. Sunscreen must be applied liberally and often to be effective, and no sunscreen is completely waterproof. Q: You should apply sunscreen even on cloudy days. Can you explain why? A: Ultraviolet light can travel through clouds, so it can harm unprotected skin even on cloudy days.


let there be light

Light includes infrared light, visible light, and ultraviolet light. As you can see from the Figure 1.1, light falls roughly in the middle of the electromagnetic spectrum. It has shorter wavelengths and higher frequencies than microwaves, but not as short and high as X rays. Q: Which type of light do you think is harmful to the skin? A: Waves of light with the highest frequencies have the most energy and are harmful to the skin. Use the electro- magnetic spectrum in the Figure 1.1 to find out which of the three types of light have the highest frequencies.


the waves in sunlight

Electromagnetic waves are waves that carry energy through matter or space as vibrating electric and magnetic fields. Electromagnetic waves have a wide range of wavelengths and frequencies. Sunlight contains the complete range of wavelengths of electromagnetic waves, which is called the electromagnetic spectrum. The Figure 1.1 shows all the waves in the spectrum.

visible light

The only light that people can see is called visible light. This light consists of a very narrow range of wavelengths that falls between infrared light and ultraviolet light. Within the visible range, we see light of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light, which has the shortest wavelength (see Figure 1.2). When all of the wavelengths of visible light are combined, as they are in sunlight, visible light appears white.


infrared light

Light with the longest wavelengths is called infrared light. The term infrared means below red. Infrared light is the range of light waves that have longer wavelengths and lower frequencies than red light in the visible range of light waves. The sun gives off infrared light as do flames and living things. You cant see infrared light waves, but you can feel them as heat. But infrared cameras and night vision goggles can detect infrared light waves and convert them to visible images.

instructional diagrams

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sunlight carries the complete range of wavelengths of electromagnetic waves.

-->  a. true

b. false

light includes

a) visible light.

b) ultraviolet light.

c) infrared light.

-->  d) all of the above

sources of infrared light include

a) the sun.

b) flames.

c) living things.

-->  d) all of the above

visible light with the highest frequencies appears to our eyes as the color

a) red.

b) yellow.

c) green.

-->  d) violet.

ultraviolet light can be used to kill bacteria in food.

-->  a. true

b. false

diagram questions

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