Chapter 4 - Waves #2 Flashcards
What is refraction?
The change of direction and speed of a wave when it crosses a boundary at an angle.
What increases the amount by which waves spread out during diffraction?
The closer the gap is to the wavelength, the greater the amount of diffraction.
What is superposition?
The effect of two waves adding together when they meet.
What is a supercrest?
Where a crest meets a crest.
What is a stationary wave?
A wave that oscillates in a fixed position.
The superposition of two progressive waves with the same frequency (and wavelength), moving in opposite directions.
What is a progressive wave?
A wave which travels through a substance or through space if electromagentic.
What is a minimum?
The resultant displacement when a crest meets a through of a different amplitude.
What are nodes?
Points along a stationary wave where the displacement is always zero.
What is interference?
The combination of two coherent progressive waves though superposition forming a resultant wave consisting of points of reinforcement (by constructive interference) and cancellation (by destructive interference).
What is the fundamental mode of vibration (first harmonic)?
The stationary wave with the lowest possible number of nodes and thus lowest frequency.
What are antinodes?
Points along a stationary wave that oscillate with maximum displacement.
How are points of cancellation created?
When crests meet troughs and create gaps between wavefronts.
What is the distance between adjacent nodes?
1/2λ
What is the principle of superposition?
When two waves meet at a point, the total (resultant) displacement at that point is equal to the vector sum of the displacements of the individual waves.
What are coherent waves?
Waves with the same frequency and constant (fixed) phase difference.
Using the same source is a good way of producing coherent waves.
What are wavefronts?
Equally spaced lines of constant phase (e.g. peaks) with line spacing equal to wavelength.
The direction in which a wave travels is perpendicular to the wavefronts.
What is diffraction?
The spreading out of waves when passing through a gap or travelling around an obstacle.
What is path difference?
The difference between the distances from a point on an interference pattern to each source.
Constructive interference occurs when…
…Path difference, d2 - d1 = nλ
Destructive interference occurs when…
…Path difference, d2 - d1 = (n + 0.5)λ
What is Young’s Double slit experiment?
The use of two coherent sources or the use of a single source with double slits to produce an interference pattern.
What are Young’s fringes?
Alternate dark and bright fringes produced on a screen.
- A bright fringe corresponds to constructive interference.
- A dark fringe corresponds to destructive interference.
What is a diffraction grating?
A plate with thousands of parallel and equally spaced slits.
Two points are in phase if the phase difference is…
Two points are in phase if the phase difference is 0 or a multiple of 360° (a full cycle).
Two points are exactly out of phase if the phase difference is…
…an odd-number multiple of 180° (π radians, a half-cycle).
Two points are in phase if they are both at ___ _____ point in the wave cycle. Points in phase have the same ________ and ________.
Two points are in phase if they are both at the same point in the wave cycle. Points in phase have the same displacement and velocity.
To get clear interference patterns, the two or more sources must be…
…coherent.
What is intensity in the context of light?
The number of photons per second hitting a certain area.
Why is the central maximum (bright fringe) in a single slit diffraction pattern the brightest?
Because the intensity of light is the highest in the centre.
Learn how to derive diffraction grating equation!(Trigonometry!)
Look in CGP book for quick explanation.
Learn how to derive diffraction grating equation!
(Trigonometry!)
Look in CGP book for quick explanation.
