Do cell phone use cause brain tumors?
Many studies have been done to see if the radio frequency radiation emitted by cell phones causes brain tumors. As yet the results have mostly shown no link, although one study seemed to show some connection. The largest amount of radiation comes when the phone first connects to a new cell phone tower, so avoid talking while driving — which is good for other reasons as well — or when the signal is poor and the phone must emit more radiation for it to work. There is a link between having a cell phone in your pocket and a decrease in bone density in the pelvis. What can cause these problems? What is electromagnetic radiation?
Energy travels through space or material. This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic properties, so they are called electromagnetic waves. The transfer of energy from one object to another through electromagnetic waves is known as radiation.
Different wavelengths of energy create different types of electromagnetic waves (Figure below).
The electromagnetic spectrum; short wavelengths are the fastest with the highest energy.
- The wavelengths humans can see are known as visible light. When viewed together, all of the wavelengths of visible light appear white. But a prism or water droplets can break the white light into different wavelengths so that separate colors appear (Figure below). What objects can you think of that radiate visible light? Two include the Sun and a light bulb.
A prism breaks apart white light.
- The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes can see infrared energy. We feel infrared energy as heat.
- Wavelengths that are shorter than violet are called ultraviolet.
Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back from a surface. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large percentage of light. A snow field has high albedo.
One important fact to remember is that energy cannot be created or destroyed — it can only be changed from one form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy.
In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not create new energy. When energy is transformed, some nearly always becomes heat. Heat transfers between materials easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same temperature.
albedo: The amount of light that reflects off a surface; snow and ice have high albedo.
electromagnetic wave: Waves with both electrical and magnetic properties; travel by radiation.
radiation: The movement of energy through empty space between objects by electromagnetic waves.
reflection: Bouncing back. A wave bounces off a reflective surface, just as a light wave bounces off a mirror.
visible light: The portion of light in the electromagnetic spectrum that is visible to humans.
- Energy travels in waves with electrical and magnetic properties and so is called electromagnetic radiation.
- The wavelengths of visible light vary from long wavelength red to short wavelength violet. Infrared and ultraviolet wavelengths continue outward at longer and shorter wavelengths.
- The law of conservation of energy states that energy cannot be created or destroyed, it can only change forms.
Use these resources to answer the questions that follow.
1. What is the electromagnetic spectrum?
2. What is the visible spectrum?
3. Why is the visible spectrum important?
4. What pattern is unique to hydrogen?
5. What is albedo?
6. How is albedo expressed?
7. What is the albedo of snow?
8. How is the Earth's albedo determined?
9. What does MODIS do?
10. What is the Earth's average temperature?
11. What happens when the rain forests are cut down?
12. What is the average albedo of the Earth?
1. How is the light from the Sun different from the light from the Moon?
2. How does the energy that comes off a surface with high albedo differ from the energy that comes off a surface with low albedo?
3. How does a child kicking a soccer ball illustrate the law of conservation of energy?