interference

/in'teuhr fear"euhns/, n.

1. an act, fact, or instance of interfering.

2. something that interferes.

3. Physics. the process in which two or more light, sound, or electromagnetic waves of the same frequency combine to reinforce or cancel each other, the amplitude of the resulting wave being equal to the sum of the amplitudes of the combining waves.

4. Radio.

a. a jumbling of radio signals, caused by the reception of undesired ones.

b. the signals or device producing the incoherence.

5. Football.

a. the act of a teammate or of teammates running ahead of a ball-carrier and blocking prospective tacklers out of the way: to run interference for the halfback.

b. such a teammate or such teammates collectively: to follow one's interference.

c. the act of illegally hindering an opponent from catching a forward pass or a kick.

6. Aeron. the situation that arises when the aerodynamic influence of one surface of an aircraft conflicts with the influence of another surface.

7. Ling.

a. (in bilingualism and foreign-language learning) the overlapping of two languages.

b. deviation from the norm of either language in such a situation.

8. the distorting or inhibiting effect of previously learned behavior on subsequent learning.

9. Psychol. the forgetting of information or an event due to inability to reconcile it with conflicting information obtained subsequently.

10. run interference, Informal. to deal with troublesome or time-consuming matters, as for a colleague or supervisor, esp. to forestall problems.

[1775-85; INTERFERE + -ENCE]

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In physics, the net effect of combining two or more wave trains moving on intersecting or coincident paths.

Constructive interference occurs if two components have the same frequency and phase; the wave amplitudes are reinforced. Destructive interference occurs when the two waves are out of phase by one-half period (see periodic motion); if the waves are of equal amplitude, they cancel each other. Two waves moving in the same direction but having slightly different frequencies interfere constructively at regular intervals, resulting in a pulsating frequency called a beat. Two waves traveling in opposite directions but having equal frequencies interfere constructively in some places and destructively in others, resulting in a standing wave.

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▪ physics

      in physics, the net effect of the combination of two or more wave trains moving on intersecting or coincident paths. The effect is that of the addition of the amplitudes of the individual waves at each point affected by more than one wave.

    If two of the components are of the same frequency and phase (i.e., they vibrate at the same rate and are maximum at the same time), the wave amplitudes are reinforced, producing constructive interference; but, if the two waves are out of phase by ¹/₂ period (i.e., one is minimum when the other is maximum), the result is destructive interference, producing complete annulment if they are of equal amplitude. The solid line in Figures A, B, and C—> represents the resultant of two waves (dotted lines) of slightly different amplitude but of the same wavelength. The two component waves are in phase in Figure A—> but out of phase by ¹/₄ period and ¹/₂ period in B—> and C—>.

      When two stones are dropped into a pool of water, waves spread out from each source, and interference occurs where they overlap. Constructive interference results where the crest of one coincides with the crest of the other. Two wave trains of light from a double slit produce interference, an effect that is visible on a screen as a pattern of alternating dark and light bands caused by intensification and extinction at points at which the waves are in phase and out of phase, respectively.

 Interference also occurs between two wave trains moving in the same direction but having different wavelengths or frequencies. The resultant effect is a complex wave. A pulsating frequency, called a beat, results when the wavelengths are slightly different. Figures D, E, and F—> show complex waves (solid lines) composed of two component interfering waves (dotted lines), the ratio of their wavelengths being 1:2 and of their amplitudes 1:3.

      Interference between waves traveling in opposite directions produces standing waves (q.v.).

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