Reflection, Refraction and Lenses Ch. 29,30

What is reflection? Reflection occurs when a wave encounters a barrier and bounces back. Examples include echoes for sound waves and mirrors for light waves.

What is echo location?

Does all the light get through? Certain kinds of materials can both reflect and transmit waves. Water will reflect some light and transmit the rest.

What is the law of reflection? All waves follow a simple rule, The Law of Reflection. It states that “The angle of incidence is equal to the angle of reflection”.

Law of reflection

How does this apply to sports? This law also applies when playing basketball or billiards. The ball will bounce off at the same angle that it encountered the backboard or bumper.

Real or virtual? Mirrors reflect light in such a way that the image seen appears almost exactly the same as the object itself. This is called a virtual image.

How does a plane mirror work?

Image from a concave and convex mirror

What is diffuse reflection? When light hits a rough surface it is reflected in many directions. This is called diffuse reflection.

Why no echoes? Echoes reflect best from smooth surfaces and poorest from irregular surfaces. Designing auditoriums and theaters must take this into account. The science of sound is called acoustics.

What are reverberations? Multiple reflections of sound waves are called reverberations. This results in garbled sound.

What is refraction? Refraction occurs when waves are bent or change direction upon entering a different type of media.

What causes refraction? If one part of a wave is made to change its speed the result is a change in direction. An example is when light waves bend upon entering water causing objects to appear larger than they really are.

Is there a good analogy? Imagine a cart being pulled from a cement sidewalk onto sand. If it is at an angle, the wheels twist when they slow down in the sand.

It is the same for light and sound

What causes mirages? The speed of light changes as it travels through different material, including the atmosphere. This can cause interesting effects, such as mirages.

Mirages and refraction

Inverted mirages?

What is dispersion? Light bent by two non-parallel surfaces undergoes separation known as dispersion. A prism disperses white light into the colors of the rainbow.

What causes a rainbow? Rain drops do this as well creating a rainbow. The rain must be in front of you and the sun behind you in order to see this effect.

The raindrop acts like a prism, dispersing light into its component frequencies.

What is total internal reflection? There is an angle called the critical angle where a beam of light will not emerge from a transparent material. At this angle, the beam experiences total internal reflection.

Fiber optic cables take advantage of total internal reflection and act like light pipes to transmit light signals for communication.

Why are diamonds so brilliant? Diamonds have the smallest critical angle of anything in nature(24.6 degrees) and therefore light is totally internally reflected several times. This causes unexpected flashes of light to emerge .

Why does reflection make good photographs?