Question

To understand the cause of constructive and destructive interference for the double-slit experiment, and to explain how the interference pattern depends on the parameters of the emitted waves.

For this tutorial, use the PhET simulation Wave Interference. This simulation allows you to send waves through a variety of barriers and look at the resulting interference patterns.

Start the simulation. You will see three possible selections: Waves, Interference, and Slits. To change between simulations at any point, select the desired simulation on the toolbar located at the bottom of the screen. In these simulations you can choose between water waves, sound waves, or light. You can adjust the slit width and slit separation using slider bars, and you can put a barrier containing one or two slits in front of the source of the waves. There are also several measuring tools at the upper-right hand corner of the screen, including a detector that produces plots showing the wave amplitude vs. time for the location of the two sensors on the detector, which can be dragged to any location.

Feel free to experiment with all of the simulations to get a feel for how they work. When you are done, and before starting Part A, set the simulation to Waves, and select the Reset icon.

Part A

Select Light for the type of wave, adjust the wavelength so that the light is red, and increase the amplitude of the light to the max. Then, select the start button at the source location to begin producing the waves.

Light is a form of electromagnetic wave, containing oscillating electric and magnetic fields. The wave amplitude detector mentioned above shows how the electric field oscillates in time at the location of the probe. The amplitude of the wave at the location of the probe is equal to the maximum electric field measured.

How does the amplitude of the wave depend on the distance from the source?

The amplitude decreases with distance.

The amplitude increases with distance.

The amplitude is constant.

Answer 1

Relationship between distance and intensity (the inverse square law, I ∝ 1/d2), this implies amplitude is inversely proportional to distance .... thus, with increase in distance amplitude of the wave decreases