Volcanoes spew large amounts of dust and ash into the atmosphere during an eruption causing changes in the composition of the atmosphere. The volcanic dust and other particles that are released into the atmosphere scatter visible light coming from the sun and infrared radiation from the sun causing short-term cooling of the area.

### Examine the effect of dust and other particles on light.

1. Set up the laser in a darkened classroom so that it is pointed at the white piece of paper.
2. Turn on the laser and discuss how the light travels across the room to the paper, even though it is not visible until it hits the paper.
3. Have a student clap the blackboard erasers together in the path of the laser beam until the beam becomes visible. As the light from the laser hits the chalk dust, it is scattered and becomes visible. Discuss why the spot of light on the white paper dims. (because less light is reaching the paper)
4. Leave the laser on and allow the dust to settle until the beam is no longer visible. What happens to the amount of light reaching the paper?
5. Discuss why an increased amount of particles in the atmosphere can cause cooling. Experiment with different particles to see which cause the most efficient scattering of the laser.

### The Green Flash

There is a phenomenon known to sailors called the green flash. For a split second after the sun sets, a green flash appears on the horizon exactly in the spot where the sun was a second earlier. Have students look into the causes of the green flash (refraction and molecular absorption). The Mount Wilson Observatory has a good description of the Green Flash.

### Fiber Optics

The light from the laser used in this experiment traveled in a straight line. Scientists have been able to curve light beams by using a laser beam within specialized fiber. This technique, called fiber optics, allows for more control over the direction the light moves, and allows for more efficient transfer of data than over copper wires.

Research the physics behind how fiber optics works and its uses in your community (phone wires, data transfer, microscope lamps, even flexible flashlights).

### Materials

• low-power laser (one that is used as a speaker's pointer is fine)
• two blackboard erasers filled with chalk dust
• white piece of paper