Refraction and Diffraction of Waves

Refraction- The change in direction of a wave as it is transmitted from one medium to another.

Mirages are due to refraction of light. (see pic next slide). As light from the sky gets closer to the ground, the hotter air above the road causes the light to refract before it hits the road surface. Instead of reflecting off the road in a diffuse manner (and not producing an image of the sky on the surface of the road), the light from the sky refracts and gets to our eyes. Therefore, we see an image of the sky floating just slightly above the road, instead of seeing the road. This image of the sky looks very much like water on the road.

Note that sound waves can also be refracted when they pass from hot to cold air, or from humid to dry air, or vice versa. The effect of this is that objects can sound like they are in a different position than they really are, or are closer or farther away than they really are. You may have noticed that sound “carries” over calm water. The cooler, more humid air above the surface of the water refracts (bends) the sound wave away from the surface of the water, directing it more toward your ears, and the object producing the sound (like a distant boat or a duck) sounds like it is closer to you than it really is.

Diffraction- The bending of a wave around or behind an obstacle Notice the water behind the wave barriers is still experiencing wave action.

Imagine the “source” to be a person talking in the bathroom Imagine the “source” to be a person talking in the bathroom. The “receiver” is one of us in my classroom. We might still hear the person talking, because the sound wave can diffuse through the bathroom doorway into the hallway, and then into my classroom.

Normally, radio waves would be blocked by the mountain Normally, radio waves would be blocked by the mountain. But the house might still be able to tune into the radio station because the radio waves diffuse behind the mountain to the house.