Straight line propagation of light

Description: Straight line propagation of light is demonstrated by spreading chalk dust in a laser beam.

The laser is set up to shine across the lecture hall. Turn off the lights. Clap the two chalk erasers together as you walk along the beam. Holding the erasers just under the beam seems to work well.

Reflection may be demonstrated by holding a mirror in the beam so that the incident and reflected rays will be scattered by the chalk dust.

Although a very simple demonstration, it usually gets a good response.

Cautions: Laser light. Use the standard precautions. Room lights need to be off.

Concepts demonstrated: Straight line propagation of light

Equipment:He-Ne laser on stand, 2 chalk erasers and chalk dust (these should be taken along - the SFU administration is on record as saying that the university has no obligation to provide chalk in the lecture halls, and indeed has not on more occasions than I care to remember). Small mirror for reflection.

Setup Time: Short

Difficulty/Commitment: Straightforward

Visibility: Very visible.

References: PIRA 6A02.35

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