PHYSICS 20 MECHANICAL WAVES Interference of Waves Interference

PHYSICS 20 MECHANICAL WAVES Interference of Waves

Interference The effect of two pulses (or waves) crossing within a medium; the medium takes on a shape that is different from the shape of either pulse alone. � The pulses move through each other unchanged � Eg. You can talk at the same time as another person and both of you will be understood. � Both waves or pulses do not lose any energy Principle of Superposition � The displacement of the combined pulse at each point of interference is the sum of the displacements of the individual pulses.

Types of Interference Constructive Interference � The overlap of pulses to create a pulse of greater amplitude. Destructive Interference � The overlap of pulses to create a pulse of lesser amplitude � In a special case, where the two pulses are identical in shape and size, the displacement at all points is zero so the resultant appears as a flat line. Then the two pulses instantly reappear. Try with slinky!

Inversion of Reflected Pulses A reflected pulse must always be the negative of the incident pulse. For this reason, the sum of the displacements for a reflected wave must add up to zero In essence, the reflected wave and incident wave combine to form destructive interference.

Standing Waves Condition where the waves seem to oscillate around stationary points called nodes. Wavelength equals the distance between alternate nodes or anti-nodes In phase – Two crests or troughs occupy the same space. Produce constructive interference Out of phase – When a crest and a trough occupy the same space. Produce destructive interference

Assignment Reading: � Pearson Physics Pages 411 – 417 Questions: � Pearson Physics 8. 3 Check and Reflect � #’s 1, 2, 5, 6, 8