Waves Flashcards
Why would 2 different types of electromagnetic waves be detected at the same time in space?
They travel at the same speed
Why do you need monochromatic light in diffraction experiments?
Provides consistent wavelength, frequency, and phase so waves produced are coherent. Polychromatic light disperses different wavelengths which travel at different velocities in glass
What diffraction pattern would you get by using a white light source?
Central bright fringe with repeating spectrum on either side of the fringe
Define reflection and refraction as well as their similarities and differences
Reflection - where a wave changes direction at a boundary between two materials
Refraction - where a wave changes direction as it changes speed when passing from one medium to the other
Similarities - both change direction at boundaries
Differences - reflection only changes direction whereas refraction also changes speed
What happens when a wave slows down or speeds up when entering a new medium and in which conditions will a wave slow down?
Slows down - bends towards the normal
Speeds up - bends away from the normal
Waves move slower in denser materials and shallower water
Define coherence
(Two) Waves with a constant phase difference which produce stable and periodic interference patterns
Define path difference as well as when maximums and minimums occur
Path difference - The difference in distance that a wave travels (from another) to reach a location
Maximum - occurs when the path difference is a multiple of the wavelength/ in phase (n lambda)
Minimum - occurs when the path difference is an odd number of half wavelengths/ in antiphase (n +1/2)
What type of interference happens when a wave is:
1. In phase
2. In antiphase
In phase - constructive
In antiphase - destructive
Name the electromagnetic waves and their wavelengths (Longest to shortest wavelength)
Radio waves- Around 10^3m to 10^1m
Microwaves - Around 10^-1m to 10^-2m
Infrared - Around 10^-5m
Visible light - 400nm (Red, 4x10^-7m) to 700nm (Violet, 7x10^-7m)
Ultraviolet - Around 10^-8m
X-Rays - Around 10^-10m
Gamma rays - Around 10^-12
REMEMBER - many of the wavelengths overlap each other as EM WAVES ARE CONTINUOUS
Give the definition of a progressive wave
A wave that transfers energy (NOT MATTER!!) as a result of oscillations. All points oscillate with the same amplitude. These waves can be either longitudinal or transverse.
What is interference?
When two waves meet and superpose at a point which causes a change in overall displacement
What type of waves can be polarised?
Transverse waves
Define polarisation
When the oscillation of a TRANSVERSE wave is restricted to one plane only
A wave that is restricted to one plane is described to be plane polarised
How do you calculate the refractive index?
N = c/v
N = Refractive index - NO UNITS
C = Speed of light in a vacuum - ms^-1
V = Speed of light in a medium - ms^-1
What is the principal of superposition?
When two waves meet at a point and superpose, the resultant displacement of the wave at that point is equal to the sum of the displacement of the individual waves
What is the formula used for the Young double slit experiment
Lambda = ax/d
Lambda = Wavelength - m
a = Distance between slits - m
x = Distance between two adjacent maxima/minima - m
d = Distance between slits and screen - m
What is the formula used for a diffraction grating experiment
d x Sin(theta) = n x lambda
d = Distance between slits - m
Sin(theta) = Angle between 0th and “nth” maxima - Degrees
n = Order of maxima - NO UNITS
Lambda = Wavelength - m
Define intensity in terms of waves as well as the equations and units
Radiant power through a surface with unit area
I=P/A I=P/4pi x r^2
Base units - kgs^-3
P= power
A= area
What happens to a waves wavelength, frequency, and velocity as it enters from air into glass?
Air into glass = entering a denser material (therefore bends towards normal)
-Velocity decreases
-Wavelength decreases
-Frequency remains constant
How do you find the refractive index of a semicircular glass block using the critical angle method?
-Increase the incident angle until the ray of light suffers total internal reflection and measure the critical angle using a protractor
- Use n = 1/sinC to find the refractive index
