4 - Waves Flashcards
What is period (T)?
The time taken to complete one full oscillation
What is the unit for period (T)?
seconds s
What is frequency (f)?
The number of oscillations completed in 1 s
What is the unit for frequency (f)?
Hertz Hz or s^-1
What is amplitude (A)?
The maximum extent of an oscillation, measured from the point of equilibrium
What is the unit for amplitude (A)?
metres m
What determines the amount a ray will reflect?
the difference in density between two materials
the angle of the ray
What is refractive index?
a property of a material that determines how much light will bend for a given angle of incidence
What is diffraction?
when a wave passes through a narrow opening, it will behave as a point source and spread out in all directions
Which of the following changes when a wave is refracted: wave speed, frequency or wavelength?
wave speed and wavelength change, but frequency remains the same
What does the polarisation of light mean?
light waves (transverse) travel in different planes but with a polarising filter, all the wavelengths except the one travelling in the same plane are absorbed
What is the principle of superposition?
when two or more waves meet, their instantaneous amplitudes add together
When does constructive interference take place?
when two waves in phase interfere
the path difference between two identical waves is a whole number of wavelengths
When does destructive interference occur?
when two waves out of phase interfere
the path difference between two identical waves is an odd number of half-wavelengths
When will two waves stay in phase?
when they have the same frequency
What is the phase difference when two waves are exactly antiphase?
1/2 a wavelength
What is phase difference?
the lead or lag of one wave over the other
What is the angle difference corresponding to a phase difference of wavelength/4?
90 degrees
What is the angle difference corresponding to a phase difference of wavelength/2?
180 degrees
What does Young’s double slit experiment show?
light behaves as a wave
Why are two slits used?
to act as two light sources but with the same wavelength and frequency, so the light sources would be in phase
this means they would produce a constructive and destructive interference pattern
What occurs at the first bright fringe?
light from both sources has travelled the same distance from each source
the two waves arrive in phase
they interfere constructively
bright fringe/ maximum produced
What occurs at a dark fringe?
light from one slit has travelled exactly half a wavelength further than light from the other
the waves arrive exactly out of phase
they interfere destructively
dark fringe/ minimum produced
How does an air molecule move in a longitudinal wave?
it is displaced to the left and right
How do standing waves differ from travelling waves?
peak doesn’t travel for standing waves
standing waves can only have discrete frequencies
standing waves have nodes and antinodes
don’t propagate energy
travelling waves can have phase shifts
for standing waves, energy depends on position
How do standing waves form?
wave travels down tube and is reflected
incident waves interferes with reflected wave
wave appears to be stationary
