Waves and Quantum physics Flashcards
Define progressive waves
a wave that transmits from a region of high energy to a region of low energy
Define longitudinal wave
when particles oscillations parallel to the direction of energy transfer
Define transverse waves
when particles oscillations perpendicular to the direction of energy transfer
define displacement
how far a part of a wave is from its equilibrium position
Define amplitude
the maximum displacement from the equilibrium to the antinode
Define wavelength
the distance between 2 peaks on a displacement/distance graph
Define time-period
the time taken for 1 full wave to pass through a point
(the distance between 2 peaks on a displacement vs time graph)
define phase difference
the difference in displacement of parts of a wave expressed as an angle
define frequency
the number of waves per second passing through a point
wave speed
the distance which a wave transmits energy per second
describe how you would setup the oscilloscope
connect the source of the waves to the y-plates of the oscilloscope
adjust the y-gain and the time base until 1 full waveform is seen
describe how you would determine the frequency
measure the number of divisions for 1 full waveform
multiply the number of divisions by the x-gain to get time period
take the reciprocal of that answer to get the frequency
convert between time-period and frequency
f = 1/t
state the wave equation
v = fλ
describe the key feature of reflection
angle of incidence = angle of reflection
describe a diagram showing a light ray passing from air into a glass block and then back into air again
before hitting block: bends towards the normal
leaving the block: bends away from the normal
define polarisation
the process of restricting the oscillations of a transverse wave into only one direction
identify the tools used to make the wave-fronts easier to use
place white paper below the ripple tank
use a strobe light to illuminate the wave fronts
define intensity
intensity is the energy delivered per second per unit area by radiation (power per unit area)
relationship between intensity and amplitude
I ∝ A^2
describe the key features of electromagnetic waves
they require no particles to transfer energy
they are instead propagated by vibrations in electric and magnetic fields
they travel at 3 * 10^8 in a vacuum
state the order of magnitude of the wavelengths of the 7 parts of the electromagnetic spectrum
Gamma - 1 pm
X-ray - 0.1 nm
UV - 10 nm
Visible - 500 nm
Infrared - 0.01 mm
Microwave - 1 cm
Radio - 10^3 m
describe how to practically demonstrate the polarisation of electromagnetic waves
the microwave emitter and detector are setup to detect vertically polarised microwaves
when the aluminium gratings are parallel to the plane of polarisation, the electrons in the gratings absorb the microwaves and re-radiate them in all directions so very few are detected
if the aluminium gratings are perpendicular to the plane of polarisation, the electrons cannot absorb the microwaves and it is detected strongly
define refractive index
the ratio of the speed of light in a vacuum to the speed of light in a medium
define snells law
As a wave crosses a boundary, the product of the refractive index and the sine of the angle in that same medium to the normal is constant
n1 x sin α1 = n2 x sin α2
describe experiments to determine the refractive index of a material using Snell’s law
n1 x sin α1 = n2 x sin α2
Shine a monochromatic laser into a glass block at an angle and mark the points that the laser is emitted, enters the block and exits the block. Then calculate the angles of incidence and refraction using trigonometry
repeat this process for 7 different angles of incidence
the initial material is air so n1 = 1 so plot a graph of sin(i) against sin(r) and measure the gradient which will be the refractive index of the material
using a laser poses the risk of retina damage so care should be taken to ensure that the laser points away from the eyes of anyone around the equipment
to enable the laser to be seen and marked accurately, this experiment should take place in a room in darkness by turning off the lights and blocking external light sources
define critical angle
the angle of incidence at which the refracted ray travels along the boundary so sin(r) = 1
critical angle equation
n1 x sin α1 = n2
=> α = sin^-1(n2/n1)
state the principle of superposition
at a point where 2 waves meet, the resultant displacement will be the sum of the displacements of the 2 individual waves
describe how you could use 2 sound wave generators to demonstrate the principle of superposition
set up 2 speaker pointing towards each other
as you move between the speakers, the loudness of the sound will change depending on whether the sound waves added together(loud) or cancelled each other out (quiet)
define interference
when 2 or more waves superpose to form a resultant wave in which the displacement is either maximum or zero
define coherence
when 2 sources produce waves with a fixed phase difference
define path difference
the difference is the distance travelled by 2 waves from their source to a point where they meet
define phase difference
the difference in displacement of 2 waves expressed as an angle
describe constructive and destructive interference in terms of path difference or phase differnece
constructive interference is when 2 waves meet in phase (phase difference of 0°)
destructive interference is when 2 waves meet in anti-phase (phase difference of 180°)
describe how an interference pattern can be produced from 2 sound wave generators
2 speakers produce sound waves with a fixed phase difference
where 2 maximum meet, constructive interference occurs which is loud
where a maximum meets a minimum, destructive interference occurs which is quiet
describe the impact of young double slit experiment on the scientific communities understanding of light
before the double slit experiment, the scientific community was divided over whether light was a particle (as Newton’s said) or a wave (as Huygens said)
Interference is a purely wave phenomenon providing evidence to contradict newtons hypothesis
state the approximate formula for wavelength from an interference pattern
λ = ax / D
a is the distance between the sources
x is the distance between maxima in the interference pattern
d is the distance between the sources and the interference pattern
describe experiments to determine the wavelength of a source of electromagnetic waves using a double slit and a diffraction grating
shine light from a highly monochromatic laser onto the double slit. as lasers produce a parallel beam of light, the 2 slits will be always in phase with each other and so are coherent
measure the distance between the slits
change the distance from the slits to the screen from 1m to 5m to get 7 readings and measure the fringe separation by measuring multiple separations and divided by the number of separations.
plot a graph of fringe spacing against the distance, determine the gradient and then multiply by the slit separation to calculate the wavelength
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