Diffraction Patterns and Wave Interference

what do the dark regions in a fringe pattern correspond to? what do the bright regions correspond to?

- dark regions: destructive interference > correspond to regions where the peaks for the wave from one slit happen to coincide with the troughs for the wave from the other slit (destructive interference!) -bright regions: constructive interference >correspond to the regions where the peaks for the two waves (or their two troughs) happen to coincide (constructive interference).

what did the photoelectric effect show us about the properties of light? what does light diffraction show us? what in combination does this tell us?

- photoelectric effect showed that light has particle-like characteristics -light diffraction and interferences shows that light has wave-like properties, >>we often refer to the wave-particle duality of light: Light has both wave-like and particle-like properties.

Which of the following statements best matches how the spacing between the light sources affects the diffraction pattern? 1) Larger spacing between lights resulted in more light and dark bands observed on the perpendicular screen. 2) Larger spacing between lights resulted in fewer light and dark bands observed on the perpendicular screen. 3) Larger spacing between lights had no effect on the number of light and dark bands observed on the perpendicular screen.

1) Larger spacing between lights resulted in more light and dark bands observed on the perpendicular screen.

Compared to the waves generated by one light (no interference), the amplitude of the waves in the diffraction pattern created by two lights was: (select all that apply) 1) larger for waves in the area of constructive interference. 2) larger for waves in the area of destructive interference. 3) very small (close to zero) in the area of constructive interference. 4) very small (close to zero) in the area of destructive interference. 5) unchanged in the area of constructive interference. 6) unchanged in the area of destructive interference.

1) larger for waves in the area of constructive interference. 4) very small (close to zero) in the area of destructive interference.

Changing the wavelength of light (from purple light to red light) affects the resulting diffraction pattern. Which of the following phrases accurately completes the sentence below? (Choose as many as apply.) More light and dark bands were observed on the perpendicular screen when: 1) purple light was used. 2) red light was used. 3) light of a shorter wavelength was used. 4) light of a longer wavelength was used. 5) light of a lower frequency was used. 6) light of a higher frequency was used.

1) purple light was used. 3) light of a shorter wavelength was used. 6) light of a higher frequency was used.

what happens if light passes through a slit? what happens to wave passing through two small openings spaced closely together ?

If light passes through a slit, it will also produce a similar wave pattern as a water wave - wave passing through two small openings spaced closely together will spread out and begin to interfere

what would the fringe patterns of a short wavelength look like? long wavelength?

If you were to pass short and long wavelength light through a set of slits, --the shorter wavelength light will produce more closely spaced fringes than longer wavelength light.

How are the wave patterns of one light source and of two light source different?

Wave interference is observed in the wave pattern for two light sources, but not in the wave pattern for one light source.

Key Concepts and Summary

Waves exhibit diffraction and interference. Electromagnetic radiation that passes through two closely spaced narrow slits having dimensions roughly similar to the wavelength will show an interference pattern that is a result of constructive and destructive interference of the waves. Since light is diffracted when passing through narrow slits, and since light can produce interference patterns, we say that light behaves as a wave. These processes cannot be explained by particles moving according to classical mechanics.

When the light passes through the two slits, each slit effectively acts as what? resulting in what?

a new source > resulting in two closely spaced waves coming into contact at the detector

Diffraction of waves occurs when?

a wave encounters an obstacle—the wave appears to bend around a small obstacle or spread out in semicircles after an opening.

what happens to the amplitudes of the interfering waves?

add together and produce a resultant wave

what do fringe patterns produced depend on?

depend on the wavelength

a plane wave comes from the left and is incident on two slits, what happens?

diffracts the plane wave -An interference pattern is produced

what happens when light passes through narrow slits closely spaced about a wavelength apart? what property of light does this demonstrate?

interference patterns arise similar to water -demonstrates wave-like nature -The fact that an interference pattern occurs indicates that a pure particle definition of light is not accurate.

Destructive interference

occurs in regions where the peak of one wave coincides with the trough of another wave (waves cancel out)

Constructive interference

occurs in regions where the peaks or troughs for the two waves coincide (produces larger wave)

diffraction

the process by which a beam of light is spread out upon encountering an obstacle in its path, typically accompanied by interference between the wave forms produced

What happens when two or more waves come into contact?

they interfere with each other

destructive interference

when the peak of one wave coincides with trough of another wave to either cancel the wave entirely or produce a smaller wave

constructive interference

when the peaks or troughs for two waves coincide to produce a wave that is the sum of the two individual waves

what would happen when when light passes through narrow slits closely spaced about a wavelength apart is light had pure particle-like properties?

would result in just two lines on the screen (one for the light particles passing through each slit).