1.
When you look at the screen, how would you describe the pattern of light and dark spots that you observe? Why do you think this pattern appears?
Section 18.1 A Wave Model for Light
In everyday experiences, light often behaves in a way that is consistent with the ray model, which assumes that light travels in straight lines, somewhat like an ordinary particle of matter. However, in some situations light also exhibits wavelike properties.
Subsubsection Video Exploration: Light as a Wave
Exercises Wave Model Simulation
Spend some time playing with the
light interference simulation. Click on the “Interference” tab, and on the right hand side, choose the laser pointer option. (You will revisit the other tabs in this simulation in future sections.) Make a list of your observations as you are playing with the simulation, then use your observations to answer the following questions.
2.
What happens on the screen if you separate the lasers as far as possible?
3.
What happens on the screen if you bring the lasers as close together as possible?
4.
What happens on the screen when you change the frequency?
Subsubsection Conclusion: Light Can Be wavelike
For each property of waves you have previously studied, there is a corresponding property of light.
Displacement and Amplitude.
Unlike mechanical waves that involve displacement of a physical medium, such as sound or water waves, light is an electromagnetic wave. Instead of displacement, the quantities that are described as waves are the electric and magnetic fields.
Wave Speed.
In a vacuum, light travels at a constant speed given by \(c = 299,792,458 \mathrm{~m/s}\text{.}\) In a medium, light travels at a speed characterized by the index of refraction as \(v = \frac{c}{n}\text{.}\)
Frequency and Wavelength.
Light with a different frequency (or different wavelengths) is perceived as having a different color.
Intensity.
The intensity of a light wave is still proportional to the square of the wave’s amplitude. Light with a different intensity is perceived as having a different brightness.
Superposition and Interference.
Two (or more) light waves can be added together using superposition and can give rise to interference. Light waves must typically be coherent (that is, they have the same wavelength) to exhibit interference phenomena.
References References
[1]
The Original Double Slit Experiment by Veritasium.
