Waves Flashcards
What is a progressive wave?
A moving wave that transfers energy from one place to another without transferring any material.
What does it mean if a wave is reflected?
Bounce back when they hit a boundary.
What does it mean when a wave refracts?
The wave changes direction and speed as it enters a new median
When does it mean when a wave is diffracted?
Wave spreads out as it passes through a gap or round an object.
What is displacement?
How far a point on the wave has moved from its undisturbed position
What is amplitude?
The maximum displacement from a wave’s undisturbed position
What is wavelength?
The length of one whole wave oscillation.
What is the period?
Time taken for one whole wave cycle
What is frequency?
Number of whole wave cycles passing a given point per second
What is phase?
A measurement of the position of a certain point along the wave cycle
What is phase difference?
The amount by which one wave lags behind another wave
How do to measure the speed of sound in air?
- Set up 2 microphones a set distance apart connected to the same computer with different inputs so that the signals from each microphone can be picked up.
- Use a signal generator to produce a sound from a loudspeaker and use the computer to record the time between the first and second microphone picking up the sound.
- Then measure the time delay between the first peak of the signal received by each microphone on a graph of voltage against time.
How do to measure the speed of sound in water?
- Use a ripple tank and measure the depth of the water using a ruler.
- Then turn on the ripple tank dipper and increase the frequency until the wave appears to not be moving ( a stationary wave is formed).
- Then use a ruler on a white piece of paper below to measure the wavelength between 2 peaks.
- Then repeat for different depths of the ripple tank.
- Use wave speed equation to calculate speed of sound in water.
What is a transverse wave?
Wave oscillations move perpendicular to the direction of energy propagation
What is a longitudinal wave?
Wave oscillations move parallel to the direction of energy propagation
What is a polarised wave?
A wave that only oscillates in one plane.
What is the principle of superposition?
When two or more waves pass through each other, the resultant displacement is equal to the vector sum of all the individual displacements
What is a stationary wave?
The superposition of two progressive waves of equal frequency and amplitude but opposite direction.
What is a node?
Where the amplitude of a wave equals 0
What is an anti-node?
Points of maximum amplitude
What is diffraction?
The spreading of waves as they pass through a gap of similar size to their wavelength.
What does monochromatic mean?
One colour, single frequency
What does coherent mean?
Fixed phase difference and same frequency and wavelength.
What causes bright fringes on a diffraction pattern?
It is due to total constructive interference as waves arrive at a screen in phase
What causes dark fringes on a diffraction pattern?
It is due to total destructive interference as waves arrive at a screen completely out of phase
How can you increase the width of the central maxima on a diffraction pattern?
- Increase the wavelength of the light
- Decrease the slit width
What is Two source interference?
Where waves from 2 sources (superimposing) to form a constructive and destructive interference pattern.
What is path difference?
It is a measure of how far ahead a wave is compared to another.
What is a diffraction grating?
A slide containing many equally spaced slits very close together.
What can Diffraction gratings be used for?
- Line absorption spectra
- X-ray crystallography
What is Line absorption spectra?
When you split up light from a star, the line absorption spectra shows you which elements are present in the star.
What is X-ray crystallography?
When X-rays are directed at a thin crystal sheet, a diffraction pattern is shown. The pattern can be used to measure the atomic spacing of molecules.
What is the refractive index?
It is a property of a material which measures how much it slows down light passing through it.
What is the critical angle?
Where the angle of refraction is equal to 90°
What is total internal reflection?
Complete reflection if a ray of light in a medium.
What is an application of TIR?
Optical fibres carrying information in the form of pulses of light.
- Internet data
- Light can carry more information due to its high frequency
- Light doesn’t heat up the fibre, therefore there is very little energy dissipation
- Minimal signal loss
What are the 2 types of signal degradation?
- Absorption: part of the signals energy is absorbed by the fibre reducing the amplitude of the signal
- Dispersion: this caused pulse broadening. Broadened signals can overlap causing a loss of information.
What are the 2 types of Dispersion and what can be used in order to reduce this?
- Modal Dispersion: Because rays of light enter the fibre at different angles, some TIR more than others, leading to shorter and flatter paths.
Solution: make core narrower - Material Dispersion: light of different frequencies travel at different speeds along the fibre, therefore taking different amounts of time to arrive.
Solution: use monochromatic light
An optical fibre repeater reduces both absorption and dispersion by regenerating the signal during its travel.
What is the description of the pattern produced when monochromatic light passes through a very narrow slit?
A wide central maximum with narrower side fringes.
A diffraction pattern is formed by passing monochromatic light through a single slit. If the width of the single slit is decreased, what happens to the width and intensity of the central maximum?
Intensity will decrease
Width will increase.
