Symmetrical Interference
Constructive and destructive interference in repeating patterns
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Video Instruction showmethephysics.com
Constructive and Destructive
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2. Symmetrical Lines of Interference - wave patterns produced
Interference Animation (Right Click, Save As)
Two Slit Diffraction
What kind of interference
What kind of interference
When crest does not align with crest,
90 degrees out of phase
Made using a spreadsheet created
Use the slider
Maximum Destructive Interference
Made using a spreadsheet created
Phase Difference - 1/2 wavelength How many degrees is the shift?
180 degrees
Double Slit
Ex) Name the interference at A, B, C, D?
June 2012
Try it yourself — tune the two speakers and match the beat.
[ Open Beat Frequency Lab in a new tab ]
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Maximum constructive interference occurs when
2. Two overlapping waves have a phase difference of ½ wavelength. How many degrees is that, and what interference results?
3. Two waves, each with amplitude 3 cm, meet in phase. What is the amplitude of the resulting wave?
4. Two waves with the same amplitude meet 90° out of phase, so crest doesn't line up with crest. The result is
5. Symmetrical lines of interference are produced by
Two Sources in a Ripple Tank
Two dippers vibrate in phase at the same frequency in a ripple tank, producing circular waves with a wavelength of 2.0 cm. The overlapping waves form a symmetrical pattern of calm lines (nodal lines) and active regions.
A point is 10.0 cm from one source and 13.0 cm from the other. What happens at that point?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. Place a check mark in three boxes to indicate the path differences that would locate a point on a nodal (calm) line in this ripple tank.
C2. The dippers’ frequency is increased. How does the pattern change?
C3. The dippers vibrate at a frequency of 6.0 Hz. Substitute numerical values into a mathematical representation that can be used to determine the speed of the water waves. Then calculate the speed.
C4. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C5. What would happen to the pattern if one dipper vibrated 180° out of phase with the other?
C6. An auditorium has two speakers playing the same steady tone in phase. Some audience members complain of “dead spots” where the tone is very quiet. Using the ripple-tank model, explain what causes the dead spots, and propose one design change that would reduce the problem.