DON’T REGRET MISSING OUT ON VALLEYFAIR

Reflection

Convex / Concave Mirrors

Diffuse Reflections

The Reflection of Sound

Convex Mirrors

• Mirrors that bulge out. Produce a virtual image that is smaller and closer to the mirror than the object is.

•http://www.edumedia-sciences.com/a309_l2-convex-mirror.html

Concave Mirrors

• Mirrors that “cave” in. Produce a virtual image that is larger and farther away from the mirror than the object is (when the object is close to the mirror).

Now I’m large enough to destroy the world! Mwa ha ha!

http://www.edumedia-sciences.com/a308_l2-concave-mirror.html

Diffuse Reflections• The reflection of waves in

many directions from a rough surface.– Each ray obeys the law of

reflection, but on a rough surface, there are many different angles.

Is this a smooth surface?

For light, this is a rough surface. But for long-wavelength radio waves, this is a polished surface. It is like a mirror to radio waves.

The longer the wavelength, the more polished a rough surface looks.

Reflection of Sound

Sound is a wave, so it can be reflected.

• Sound reflects better off of rigid and smooth surfaces. Sound energy that is not reflected is absorbed or transmitted.

•Reverberation: the persistence of sound, as in an echo, due to multiple reflections.

The Concert Hall

• Too much reverberation = garbled sound

• Too much absorption = quieter, duller sound.

• We want a balance between reverberation and absorption.

• Is it better to have smooth walls in a concert hall, or to have rough walls?

The Concert Hall

• Want both!

• Grooves in the wall make sure that the sound a person hears is from many parts of the wall.

• Reflective surfaces are placed behind the stage to direct sound out to the audience.