Physics Section 3-waves Flashcards
what is a progressive wave
a wave that carries energy from one place to another without transferring material
what is reflection
when a wave bonces back when it hits a boundary
what is refraction
when a wave changes direction as it enters a different medium (due to a wave slowing down or speeding up)
what is diffraction
the wave spreads out as it passes through a gap or around an obstacle
What is displacement and what is it measured in
how far a point on the wave has moved from its undisturbed position (metres)
what is amplitude and what is it measured
the maximum magnitude of the displacement (metres)
what is wavelength and what is it measured in
the length of one whole wave oscillation ( lambda, metres)
what is period and what is it measured in
the time taken for one whole wave cycle (seconds)
what is frequency and what is it measured in
the number of whole wave cycles in a second (hertz)
what is phase difference
the amount by which one wave lags behind another
what are the two equations to find wave speed
c = d / t
c = f x lambda
what is one way to measure the speed of sound
by using two microphones in a straight line. then use a signal generator and a computer to record the time between picking up sound between the two different signals.
then use speed = distance / time to calculate the speed of the sound waves
how can you measure wave speed in water
record the depth of water in a tank using a ruler
make vibrations and turn up a strobe light above the ripple tank
increase frequency until the waves seem to be standing still
use a ruler on the white paper below the and measure two adjacent peaks
repeat at different depths
what is a transverse wave
the displacement of particles is at a right angle of energy propagation
what is a longitudinal wave
the displacement of the particles is along the direction of energy propagation
what is a polarised wave
a wave that only oscillates in one direction only
what are two ways polarisation is used in real life circumstances
glare reduction
improving tv signals and radio signals
what is superposition
when two or more waves cross, and the displacements of both the waves combine
what is constructive interference
when the displacements are in the same direction and combine to give a bigger displacement.
what is destructive interference
when a positive and negative displacement combine and cancel each other out
what is total destructive interference
when two waves with equal and opposite displacements meet and cancel each other out
how long is a cycle of a wave (degrees and radians)
360 degrees
2π radians
what is a stationary wave
the superposition of two progressive waves with the same frequency and amplitude moving in opposite directions
what happens at a node
total destructive interference
what happens at an antinode
constructive interference
what is the first harmonic
it has one loop with a node at each end so one half wavelength fits on the string
what is the second harmonic
a node in the middle and one either end and one wavelength fits on the string
what is the third harmonic
1 and a half wavelength with 4 nodes
when is diffraction at the maximum
when the wavelength is the same as the size of the gap
what does monochromatic mean
a light source with one wavelength (frequency)
why is there alternating dark and bright fringes on a screen when light is diffracted
due to constructive and destructive interference
what happens when white light is shone through a slit where diffraction occurs
all the different wavelengths are diffracted at by different amounts and on the smaller fringes a full spectra of colours can be seen
