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Oil Drop Experiment

Experiments that prove the charge of a single electron.

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Seeing the Unseeable

Seeing the Unseeable

Credit: NASA Goddard
Source: http://www.flickr.com/photos/gsfc/4398655649/
License: CC BY-NC 3.0

The Crab Nebula is but one of the many striking structures in outer space. With a low-power telescope you may be able to see it, but certainly not with the naked eye. There are many things we cannot see without the aid of some kind of scientific instrument or device. From the tiniest cellular component to the wonders of outer space, we use tools to see the unseeable.

Amazing But True

  • Humans have developed many tools for seeing what they could not otherwise see. One such tool is the microscope, allowing us to visualize small organisms and cells of the body. We can now watch red blood cells move in a capillary or detect a harmful microorganism so we will know what drug to use to treat the disease.
  • Broken bones have been a problem for humans since the beginning of time. A fall producing a broken leg, an injury in wartime – these and other problems made it necessary to be able to see the bone under the skin so that the fracture could be set properly. Development of X-rays now allows quick detection of fractures as well as the locating of abnormal tissues in the body giving rise to serious health problems.
  • Radar is a detection system that uses radio waves to learn where an object is. The first significant application of radar was during World War II when it was used to locate enemy vehicles and direct fire on targets. Today the primary use in in studying weather patterns. Every TV station has access to radar data that can be displayed for the viewing public. The National Weather Service also posts radar data on its web site.
  • Ever since the invention of the telescope by Galileo and others in the 1600s, humans have been fascinated by outer space. Using improved telescopes, vast amounts of data about planets, stars, comets, and other space bodies have been gathered. One problem with these instruments was the interference with light detection by the atmosphere. To overcome this difficulty, the Hubble telescope was launched in 1990. Orbiting above the earth at about five miles per second, the Hubble can see far into outer space and bring back images that earth-based systems are not capable of detecting.
  • Credit: NASA
    Source: http://www.flickr.com/photos/gsfc/4545825554/
    License: CC BY-NC 3.0

    This is one of the spectacular images captured by the Hubble telescope. The image is of a stellar nursery located in the Carina Nebula [Figure2]


  • Watch a video about electron microscopes at the link below:


Show What You Know

Use the links below to learn more about visualizing what we cannot see directly. Then answer the following questions.

  1. What did Leeuwenhoek see in his microscope?
  2. How did doctors use X-rays shortly after their development?
  3. What is the principle used in detection with radar?
  4. How can radar be used to detect wind velocity?
  5. What advantage does the Hubble telescope have over instruments based on the ground?

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Image Attributions

  1. [1]^ Credit: NASA Goddard; Source: http://www.flickr.com/photos/gsfc/4398655649/; License: CC BY-NC 3.0
  2. [2]^ Credit: NASA; Source: http://www.flickr.com/photos/gsfc/4545825554/; License: CC BY-NC 3.0

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