Wave Interference and Diffraction Flashcards
What happens when displacements not too large come from a point source
A spherical wave is produced
What is Huygens-Fresnel principle
Each point on a wavefront is itself a source of spherical waves
What does a wavefront represent
A point on all the waves which are in the same phase, amplitude and propagating in the same direction.
What colours are typically used to represent wavefronts and for what specific condition
Grey for maximum amplitude
Black for minimum amplitude
What happens to wavefronts on a spherical wave when going through a more optically dense region
Wavelength between the wavefronts on the spherical waves is smaller than the wavefronts before the boundary
When is diffraction greatest
When the gap is a similar size to the wavelength
What happnes if the gap is smaller than the wavelength
Most the wave is reflected
What happens during diffraction
Waves bend around opaque structures
What happens when waves meet an opaque obstacle
You will get diffraction around the edges
There will be a region where not enough diffraction occurs to fill the space with the wave, hence this wave-empty region is referred to as a shadow
The shadow just forms where there is destructive interference
Larger the obstacle, the larger the shadow
What is the diffraction pattern for monochromatic light
Central fringe is brightest
Fringes reduce is intensity as you go further way from central fringe
Bright fringes are due to maximum constructive interference
Dark fringes are due to total destructive interference
Smooth transitions of intensity between bright and dark du to partial constructive and destructive interference
Relationship between slit size and diffraction
Larger the slit size, less diffraction
The greater the gap compared to wavelength,higher central intensity is???
Higher
What does the width of the central maximum depend on
Wavelength of light and the slit size
Smaller wavelength, decreases diffraction, central intensity increases as it is spread out less
Diffraction of white light
Red light wll be diffracted the most as it has the longest wavelength
Purple diffracts the least as it has the shortest wavelength
When do clear diffraction patterns form
When light is monochromatic, coherent and lasers are used
When are waves coherent
Waves have the same frequency and fixed phase difference and same waveform
What is path difference
Difference in distance travelled when interfering wave travel to the meeting point due to starting from different sources
Path difference formula
Constructive interference: p.d = n x lambda
Destructive interference: pd = (n + 1/2) x lambda
n = fringe number (0,1,2)
Double slit formula
W = (lambda x D) / s
distance between fringes = (Lambda x distance to screen) / spacing between slits
Diffraction grating formula
n x lambda = d x sin(theta)
Properties of laser
Monochromatic
All in phase and coherent leads to high directionality
High intensity
Can be continuous or very short pulses
Laser safety precaution
Can destroy eyesight due to how coherent they are - use specialised glasses
Mount at waist height so stray beams avoid the face
Warning lights and signs
