COMBINING WAVES Flashcards
Define Phase Difference.
Difference in angle of the vectors corresponding to two points on the same wave.
State conditions for stationary wave to be formed.
Must have the same frequency/wavelength.
Similar amplitudes.
Travelling past eachother in opposite directions.
Describe nodes and antinodes.
Nodes are points on a stationary wave that have no vibration.
Antinodes are points of vibration at maximum amplitudes.
Define Principle of Superposition.
The vector addition of the displacements of the two waves overlapping.
What are harmonics?
Different wave patterns in a stationary wave. Depends on frequency of vibration.
How does interference occur?
When waves overlap and resultant displacements equal the sum of displacements of each wave (principle of superposition.)
Define coherence.
Waves said to be coherent when they have same frequency and a constant phase difference.
Define path difference.
Difference in distance travelled by two waves from their sources to the point they meet.
Describe interference in context of two speakers.
The two sources are coherent.
When the path difference is a whole number of wavelengths the two waves are said to be in phase. From the principle of superposition constructive interference occurs where the amplitudes add together causing a maximum or LOUD region.
When the path difference is a half number of wavelengths the waves are said to be in antiphase. This causes destructive interference to occur where amplitudes cancel out giving a QUIET region.
Describe Young’s Double Slit Experiment.
To work must have two sources that are coherent and monochromatic.
When two waves interfere resultant wave depends on the phase difference(proportional to path difference).
If path difference whole number of wavelengths we get constructive interference.
If half number of wavelengths we get destructive interference.
This experiment produces visible interference pattern on a screen.
W = (lambda D) / s
What if source was replaced with white light? (Young’s Slit)
White light composed of all colours so each wavelength produces interference pattern.
Central fringe white light as path difference for all wavelengths 0 so all in phase.
Blue appears closest as has shorter wavelength so path difference smaller = closer to centre.
Describe Single Slit Diffraction.
Central maximum with high intensity.
Subsidiary maxima equally spaced smaller in intensity half width.
How does changing aperture width affect single slit diffraction?
Increasing width less spread out and light intensity increases.
Decreasing width more spread out less light intensity.
How does changing wavelength affect single slit diffraction?
Longer wavelength more spread out.
Shorter wavelength less spread out.
How does changing distance from slit to screen affect single slit diffraction?
Increasing distance more spread out.
Decreasing distance less spread out.
