Flashcards in Waves Deck (49)
What is a PROGRESSIVE WAVE?
It moves energy from one place to another without transferring any matter
How does a WAVE work?
Either matter or a field oscillates at a source, which passes through a medium or field when it oscillates which takes energy away from the source
Describe a reflection
When a wave is bounced back when it hits a boundary
Describe a refraction
When the wave changes direction as it enters a different medium - as a result of the wave slowing down or speeding up
Describe a diffraction
When the wave spreads out as it passes through a gap or round an obstacle
What is displacement in terms of waves?
How far a point on a wave has moved from its undisturbed position
What is amplitude in terms of waves?
The maximum magnitude of displacement that a wave can be from an undisturbed position.
What is wavelength in terms of waves?
The length of one whole oscillation (length between two whole crests or two equal point on a wave)
What is a period in terms of waves?
The time taken for one whole wave cycle
What is frequency in terms of waves?
The number of whole waves passing a certain point per second
What is a phase in terms of waves?
A measurement of the position of a certain point along the wave cycle
What is phase difference in terms of wave?
The amount which one wave lags behind another wave
can be measure in degrees, radians, or fractions of a cycle
What is the equation for FREQUENCY?
f(Hz) = 1
What is the equation for WAVE SPEED
Wave speed = frequency x wavelength
or wave speed = distance/time
c(ms^-1)=f(Hz) x lambda(m)
What is the speed of an EM wave is a vacuum?
3 x 10^8 (ms^-1)
How could you measure the speed of a wave in water?
1. Set up a ripple tank with a strobe light over it with a signal generator and a ripple tank dipper
2. Measure the depth of the water, then set the dipper to a frequency with regular vibrations
3. Dim the rooms light and match the strobe light frequency so that the waves appear to be standing still
4. Record the frequency on the signal generator and the distance between adjacent peaks and then dividing it by the amount of troughs in between them
5. Then use the equation c=f x wl to calculate the wave speed
What is a TRANSVERSE WAVE?
It is a wave that oscillates particles or the field perpendicular to the direction of travel
How could you draw a transverse wave on a graph?
Displacement against time
Displacement against distance
What is a LONGITUDINAL WAVE?
It is a wave that oscillates particles or the field parallel to the direction of travel
What is a polarising filter?
A filter that only lets light waves oscillate through it in one direction - so if you had two filters at right angles to each other no light could pass through
What are the uses for polarising filters?
To reduce glare in sunglasses
To improve TV and radio signals
When does superposition occur?
When two or more waves pass through each other - the displacements in each wave combine
What is constructive inference?
When waves meet and their displacements are in the same direction they combine to make a larger net displacement
What is destructive interference?
When waves meet and the positive displacement of one wave meets a wave with a negative displacement of another wave and cancel each other out
What is total destructive interference?
When two waves of equal and opposite displacements meet and completely cancel each other out
What is a stationary wave?
When two progressive waves superposition and they have the same frequency(or wavelength) and amplitude and are moving in opposite directions
Do stationary waves transmit energy?
What is a resonant frequency?
When a source produces an exact number of waves in the time it takes a wave to get to be reflected
What does a resonant frequency cause on a string?
A stationary wave where the pattern does not move it just vibrates up and down