Go to http://phet.colorado.edu/en/simulation/legacy/wave-interference and click
ID: 3163828 • Letter: G
Question
Go to http://phet.colorado.edu/en/simulation/legacy/wave-interference and click 'Run Now!' to start the *Wave Interference' simulation. Click on the 'Light' tab towards the upper left, then click the 'Show Screen' button on the right, then click the 'Intensity Graph' button that just appeared. This produces a picture of a viewing screen and a graph of the intensity of the light on that viewing screen. Describe your observation of the viewing screen and the graph. It might not be clear at this point just what the simulation is showing you (what the ripples, the screen, or the graph represent). Click on the "Add Detector" button to add an electric field detector to the simulation. It will measure the electric field as a function of time at the location of the cross hairs. a. Click on the radio button labeled Two lights'. Set the spacing to one tick mark from the right. Describe in detail your observations of what happens to the screen, the graph, and the region between the lights and the screen. b. Now turn off the top light and wait. What happens? Suggest an explanation for why the viewing screen and graph change so dramatically with one light on versus two. c. Return to the 'One light' setting but shorten the wavelength of the light so that it is blue or violet. Also increase the amplitude to maximum. Describe your observations of the viewing screen and the graph. d. Now switch to the two-light setup from #2 above. Describe in detail your observations of what happens to the screen, the graph, and the region between the lights and the screen. Describe how it is different from what you observed in #2. e. Click "Reset Air, then 'Show Screen', then 'Intensity Graph'. Increase the amplitude to maximum, and add Two slits'. Set the slit width to halfway between the 2^nd and 3^rd tick marks from the left. Set the barrier location to the middle, and the slit separation to two ticks from the right, and wait. Record your observations of the viewing screen, the graph, and the region between the barrier and the screen. f. What similarities do you notice between your observations of two light sources (#2) and a single light source with a barrier with two slits? Suggest an explanation for the similarities.Explanation / Answer
a) The screen is bright at the center and dim at the top and bottom, the graph shows high intesity at the middle and low at the ends same as what is on the screen. In the region between the lights and the screen , the two waves form the lights merge into one and single wave front advance to screen
b) The screen is dimmer compared to two lights and the graph is uniform, as there is only one light source , there is no intefrence and the intensity is less beacuase it is from single light source.
c) The screen is bright, the graph show intesity high at the middle and low at the ends.
d) The screen is brighter and the graph show increased intensity high in the middle and dcreases towads the ends. The inetsity inscreased beacuase the amplitude add up due to ineterference. In the region between the lights and the screen, the waves combine and reache the screen. The inetsity is higher beacuase the amplitudes of the lights are larger.
e) on the screen we see band of dark and bright patches. In region we see wave fronts advance from the slits and consbine near the screen producing dark and bright patches on the screen. The graph shows a damping eletric wave, the intesity decreases with position.
f) In both cases the light waves interfere, In case of tow light sources they amy not are coherent and we do not see a clear inetefrence as in the casee of two slits.
b)
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