RADIO WAVES Radio waves are made by various types of transmitter, depending on the wavelength. You can tune a radio to a specific wavelength or

Transcription

1 RADIO WAVES Radio waves are made by various types of transmitter, depending on the wavelength. You can tune a radio to a specific wavelength or frequency and listen to your favorite music. The radio "receives" these electromagnetic radio waves and converts them to mechanical vibrations in the speaker to create the sound waves you can hear. Radio waves are also given off by stars, sparks and lightning, which is why you hear interference on your radio in a thunderstorm.

2 MICROWAVES You may be familiar with microwave images as they are used on TV weather news and you can even use microwaves to cook your food. Microwave ovens work by using microwave about 12 centimeters in length to force water and fat molecules in food to rotate. The interaction of these molecules undergoing forced rotation creates heat, and the food is cooked. Microwaves work well for cooking because their energy can be efficiently absorbed by molecules commonly found in food, including water, sugars, and fats. The absorbed microwave energy heats these molecules and cooks the food. In a microwave oven, interference occurs between waves that are reflected from the inside surfaces of the oven. The interference patterns can create "hot" and "cold" spots in the oven areas where the microwave energy is higher or lower than average.

3 INFRARED RADIATION The front end of a remote control has a small light bulb. When you press a button on the remote, it sends out an infrared light signal. A detector on the TV gets these signals and tells the TV what you want it to do. Infrared light has a slightly longer wavelength than visible light. The remote control system won't work if someone walks between it and the TV because the infrared signal is absorbed by the person. Similarly, it doesn't usually work if you point it away from the TV because the signal doesn't hit the detector. Try to get the remote and the radio to work in the following scenarios Try to change stations or the volume o Normal nothing between the remote and the radio o Through a plastic bag filled with water o Through a black plastic trashbag o Through a piece of plastic o Pointing in away from the radio and hitting a mirror or cd o Through a piece of white paper

4 VISIBLE LIGHT All electromagnetic radiation is light, but we can only see a small portion of this radiation the portion we call visible light. A prism divides light into the wavelengths that make it up. Seen together, color waves make white light. White light is especially dramatic because many different colors of the visual spectrum can combine to make white light. When white light shines on a prism, the colors in white light separate from each other because they refract at different angles depending on their wavelength. Water droplets in the air refract sunlight to create rainbows. Place the CD (label up) on an angle on top of the projector. This should create a rainbow on the wall. Use what you see to answer the following questions. Be careful do not look into the projectors light or send reflections of light from cd into the classroom!

5 ULTRAVIOLET RADIATION The energy from the sun includes not only visible light but also wavelengths longer (infrared) and shorter (ultraviolet) than visible light. Ultra means beyond, so ultraviolet means beyond (actually, shorter than) violet. The amount of UV radiation reaching the earth's surface at a particular point depends on the distance it travels through the atmosphere. During morning hours, UV radiation must travel through more of the earth's atmosphere because the sun is lower on the horizon. At noon the rays travel a shorter distance through the atmosphere because the sun is more directly overhead SEE YOUR TEACHER FOR A PIECE OF UV SENSITIVE PAPER! USE THE PLASTIC COVER TO HOLD YOUR SHAPE IN PLACE WHEN YOU PLACE IT BY THE WINDOW.

6 X RAYS Xrays are types of waves in the electromagnetic spectrum. They are very high frequency waves, and carry a lot of energy. They will pass through most substances, and this makes them useful in medicine and industry to see inside things. In medicine, they are used to determine if you have a broken bone or other medical conditions. A technician takes and places a piece of film (just like a negative of a camera) underneath the area they want to see. The Xray waves are then shot through the area onto the film.

7 X RAYS STATION 2 Follow the procedure below to determine how an x ray works? 1. Place a piece of ordinary window screen over the circular pan. 2. Place a foam cutout on top of the screen. 3. Sprinkle sand over the area of the pan. 4. Carefully lift the screen and observe the inside of the pan. 5. Clean up sand out of bottom of pan and surrounding area. 6. Place sand back in its container.

8 GAMMA RAYS SCIENCE & ENVIRONMENT Gamma ray burst brightest ever seen By Rebecca Morelle Science reporter, BBC World Service A cosmic explosion caused by the death of a massive star has been analysed by scientists. The blast of radiation, called a gamma ray burst, was spotted earlier this year by space based telescopes and has been confirmed as the brightest ever seen. Researchers believe the distant star was about times the mass of the Sun. The findings are published in the journal Science. The researchers say it took the light from this event about four billion years to reach us. Astronomer Prof Paul O'Brien, from the University of Leicester, said: "These events can happen in any galaxy at any time. We have no way to predict them." Devastation The monstrous blast from the dying star was spotted by Nasa's Swift and Fermi space based telescopes. The explosion would have lasted for less than a minute, but hurled radiation across the cosmos. "The star was previously living quite happily, fusing material in its core. And then it ran out of fuel," explained Prof O'Brien, who is part of the Swift team. The core of the star would have collapsed into a black hole, while liberating a powerful jet of energy the gamma ray burst. A blast wave would have also caused the rest of the star to expand outwards, creating another dazzling event called a supernova. "We can see the decaying light the remnants of both events for weeks or months afterwards," said Prof O'Brien. Although the event was closer to Earth than most gamma ray bursts that have been detected, the radiation would have posed no danger. Once it reached our planet, the energy would have been absorbed by our atmosphere. However if a similar explosion happened closer to home, within a distance of 1,000 light years, it could damage the ozone layer, with devastating consequences for life on Earth. "The prediction is that there would be one [gamma ray burst] close to the Earth to do us harm every 500 million years," said Prof O'Brien. "At some point in the Earth's history we probably were irradiated by a gamma ray burst, and it will happen again at some point in the future. "But the chances of it happening in our lifetime are very low."