Waves Flashcards
What is a progressive wave?
A wave that carries energy from one place to another without transferring any matter.
What is reflection?
the wave is bounced back when it hits a boundary
What is refraction?
wave changing direction as it enters a different medium
What is diffraction?
when a eave spreads out as it passes through a gap/round an obstacle
What’s characteristic of a transverse wave?
The oscillations ate perpendicular to wave travel/energy propagation
What’s characteristic of a longitudinal wave?
The oscillations are parallel to the direction of wave travel/energy propagatiom
What is yhe principle of superposition?
It states that when two or more waves cross, the resultant displacement equals the vector sum of the individual displacements.
What does it mean if points on a wave are in phase?
Two points are in phase if they’re at the same point in the wave cycle
What is a stationary wave?
It is the superposition of two progressive waves with the same frequency and amplitude moving in opposite directions. No energy is transmitted
What are nodes?
Points on a stationary wave where amplitude is always equal to 0.
What are antinodes?
Points on a standing wave with maximum amplitude.
Factors affecting resonant frequency
The longer the string the lower the resonant frequency (c=wavelength x frequency)
The heavier the string the lower the resonant frequency because waves travel slower in the string
The lower the tension on the string the lower the resonant frequency
What does diffraction through a single slit look like?
Central bright maxima, with alternating dark and bright coloured fringes on either side. (rude diagram)
How does the width of the central maximum vary with a wider slit (single slit)?
Increasing slit width decreases the amount of diffraction.
Central maximum narrower.
Intensity is higher.
How does changing the wavelength affect the central maximum (single slit)?
Increasing the wavelength increases the amount of diffraction.
Central maximum is wider.
Intensity of central maximum is lower.
When does constructive interference occur?
When n wavelength is a whole number
What safety precautions should you take when working with lasers?
Never shine laser at a person
Don’t shine at a reflective surface
Wear laser safety goggles
Have a warning sign
Turn laser off when not needed
Who suggested the wave nature of light in the 1700s?
Huygens
What type of fringes do diffraction gratings produce?
Equally spaced bright spots
What uses do diffraction gratings have?
They can be used for line absorption spectra, to help identify the different gases in star’s atmospheres etc.
They can also be used for X-ray crystallography, x ray wavelengths are similar to the spacing between the atoms in crystalline solids, this can produce diffraction patterns.
If light bends away from the normal when refracted, what must be true about the n values?
n1>n2
If light bends towards the normal when refracted, what must be true about the n values?
n1<n2
When does total internal reflection occur?
When n1>n2 and theta 1>=theta c
What are the values for n in fibre optic cables?
n core>n cladding
Why is the cladding useful (other than TIR)?
it helps protect the core from micro fractures that disperse tbe light and can disrupt the signals
What are advantages of fibre optical TV?
signal carries more info because it has a higher frequency
Light doesn’t heat up the fibre so no energy is lost through heat
No electrical interference
Fibre optic is cheap
Signal travels a long way
What are the issues with fibre optic?
SIGNAL DEGRADATION
Absorption
Modal dispersion
Material dispersion
Define signal absorption and how it affects the signal
When signal energy is lost due to the material absorption creating a loss in signal amplitude
Define modal dispersion and how it affects the signal, and how it can be helped
Different paths taken by the light waves due to coming in at different angles
Waves reach the end at different points resulting in pulse broadening
Thin the core to prevent this
Define material dispersion and how it affects the signal, and how it can be prevented
When different wavelengths of light travel different distances, due to different wavelengths refracting differently resulting in pulse broadening.
Use monochromatic light
