April 1, 2012 Issue

Physics To Go 123 - Making electromagnetic waves

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Physics in Your World

Hyperphysics: Electromagnetic Waves image
image credit: CERN; image source; larger image

Hyperphysics: Electromagnetic Waves

In the photo above of a handheld citizens band radio, the metal coil is the antenna. When the radio is transmitting, the radio produces an electric current that surges back and forth in the antenna, which emits radio waves. And when the radio is receiving, radio waves induce a tiny alternating current in the antenna. The current in the antenna carries the radio signal.

For a drawing of an electromagnetic wave (radio waves are one example) see Hyperphysics: Electromagnetic Waves. To learn more about the CB antenna shown in the photo, go to this Wikipedia article and scroll down.

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Physics at Home

PhET Simulation: Radio Waves & Electromagnetic Fields

Security note:
Once you have clicked on the "simulation" link below, be sure to read the Java Security Advisory before running the simulation: To do that, click the "Read now" button on the yellow band near the top of the PhET page.

Shake a charged particle, and it radiates electromagnetic waves. You can try this out with the PhET Simulation: Radio Waves & Electromagnetic Fields. Compare with Physics in Your World above.

To learn more, check out these Physics 2000

(This feature was updated on May 5, 2013.)


From Physics Research

X-rays from free electrons image
image credit: CERN; image source; larger image

X-rays from free electrons

The spiral track above was made by an electron moving in a magnetic field. Since motion along a curved path requires a force perpendicular to the direction of motion, the electron is accelerated. Accelerated charges radiate electromagnetic waves, so the electron loses energy and spirals inward. To learn more about this process, see X-rays from free electrons.

Worth a Look

Hyperphysics: X-ray tube

X-ray tubes work by firing electrons at a metal plate in a vacuum. When an electron passes near the nucleus of one of the atoms in the plate, it is accelerated and emits x-rays, as shown in the drawing on this Hyperphysics page. To learn more, visit Hyperphysics: X-ray tube.

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