Properties of waves and Light

Historically Isaac Newton believed light was made up of fast moving, tiny particles.

Others believed there was another explanation -Waves

Both models had their problems

Diffraction is…

the bending of waves, esp. sound and light waves, around obstacles in their path.

Diffraction of Waves (In Very Simple Terms) Diffraction is the spreading of a wave as it goes through a narrow gap or passes round a small obstacle.The effect of diffraction increases when the width of the gap is decreased.

The effect of diffraction increases when the wavelength is increased.

Refraction of Waves is the bending of a wave when it enters a medium where it's speed is different. The refraction occurs when it passes from a fast medium to a slow medium bends toward the normal to the boundary between the two media.

The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law

Interference is… the process in which two or more waves

combine to reinforce or cancel each other, the amplitude of the resulting wave being equal to the sum of the amplitudes of the combining waves.

ConstructiveInterference

Destructive Interference.

Constructive Interference. Tipler, Paul A. Physics for Scientists and Engineers. 4th Ed. New York: W.H. Freeman and Company, 1999.Destructive Interference. Tipler, Paul A. Physics for Scientists and Engineers. 4th Ed. New York: W.H. Freeman and Company, 1999. 

Does light do all of these things?

More investigation was needed

Two scientist help move the Wave theory of light forward

Christian Huygens and Thomas Young

• The Dutch scientist Christian Huygens (1629-1695) proposed a wave model to explain diffraction and refraction.

• Huygens principal :Light sources consist of an infinite number of points, which generate a plane wave front.

http://demonstrations.wolfram.com/HuygenssPrinciple/

http://www.walter-fendt.de/ph14e/huygenspr.htmRefraction using Huygens

When Light Waves Interfere

Youngs' double slit Experiment

When Light Waves Interfere

Youngs' double slit Experiment

Young measured light's wavelengths and provided additional evidence of the waves nature of light. By directing the beam of light at two narrow, closely spaced slits in barrier, light diffracted and the two waves interacted . This created an interference pattern of light and dark bands.

Where two crests overlap (waves interfere constructively), light intensity increases creating a bright band on screen. Crests and troughs meet (interfere destructively) and cancel one another to create dark region.

Diffraction of white light.

White light in double slit diffraction causes colors instead of light/dark bands. Positions of constructive/destructive bands depends on light's wavelength.

Christian Huygens and Thomas Young

successfully related the properties of waves and light and validated the wave theory of light.

Interference patterns analysed

Interfrence patterns depend on wavelength therefore by

analysing the pattern you can measure the Wavelength of a

Light Wave

Equation: Wavelength Using Double Slit Interference

Single-Slit Diffraction