Wave Properties (Unit 2) Flashcards
What is diffraction?
- spreading out of waves when they meet obstacles, such as the edges of a slit
What happens when the wavelength is much smaller than the size of the slit or obstacle?
-there is little diffraction
-the main beam spreads through less than 180°
If wavelength is equal to or greater than the width of a slit, how do waves spread?
waves spread as roughly semi-circular wave fronts,
How does two source interference occur?
When waves from two sources pass through the same medium at the same time, they combine together
For two source interference to be observed clearly, the sources must have?
-a zero or constant phase difference
-oscillations in the same direction.
What does young’s double split experiment show?
light has wave-like properties.
What is the principle of superstition?
if waves from two sources occupy the same region, then the total displacement at any one point is the vector sum of their individual displacements at that point
What happens if the path difference is a whole number (integer) of wavelengths?
the waves arrive at P in phase which means that constructive interference will occur.
What happens if the path difference is a odd number of half wavelengths?
The waves arrive at P in antiphase which means that destructive interference will occur.
As a result of constructive interference, the resultant wave has an increased ?
Amplitude
In Young’s experiment, CONSTRUCTIVE interference will results in WHAT fringe on the screen?
Bright fringes
In Young’s experiment, DESTRUCTIVE interference will results in WHAT fringe on the screen?
Dark fringes
What does a diffraction grating do differently to Young’s double split?
-a very small slit separation makes beams (“orders”) much further apart than in Young’s experiment,
-large number of slits makes the bright beams much sharper
Coherent sources emit what kind of waves?
are monochromatic with wave fronts continuous across the width of the beam
How do we know if two sources are coherent?
-a constant phase relationship constantly in phase or CONSTANTLY out of phase).
- produce waves of same frequency and amplitude
Examples of coherent sources?
laser, single slit aperture
Examples of incoherent sources?
sunlight, light bulbs
How can two source interference be observed?
two waves must be coherent
-direction of polarisation is common
What do STATIONARY WAVES have?
- do not transfer energy
- the amplitude is zero at the nodes and increases to a maximum at the antinodes and decreases back to 0 at the next node
-frequency is same for all particles except at nodes
-all the particles between two adjacent nodes have the same phase but are in antiphase with those in the next loop
What do PROGRESSIVE WAVES have?
-Progressive waves transfer energy
-Amplitude does not change
-All particles vibrate with the frequency of the wave
-all the particles within one wavelength have a different phase, between 0 and 2 pi
What can a stationary wave be regarded as?
superposition of two
progressive waves of equal amplitude and frequency, travelling in opposite
directions
What is the internodal distance?
Pi/2
Wavelength of a progressive wave?
-the minimum distance (measured along the direction of propagation)between two points on the wave oscillating in phase.
