Waves 1 Flashcards
Everything you need to know to get A* in OCR Physics A Level, closely following the specification and the textbook
What is a progressive wave?
A wave that transfers energy from one place to another, but not matter
What is a longitudinal wave?
A wave where oscillations are parallel to the direction of energy transfer
What is a transverse wave?
A wave where oscillations are perpendicular to the direction of energy transfer
What is displacement?
Distance from equilibrium position in a particular direction
What is amplitude?
The maximum displacement from equilibrium position
What is the wavelength?
The minimum distance between 2 points in phase on adjacent waves
What is the time period?
The time taken for 1 oscillation/The time taken for a wave to move 1 whole wavelength past a given point
What is the phase difference?
The difference in displacement of particles along a wave, measured in degrees or radians
What is the frequency?
The number of wavelengths passing a given point per unit time
What is the wavespeed?
The distance travelled by a wave per unit time
What is the frequency equation?
f=1/T
What is the wave equation?
v = fλ
What is the equation to find the phase difference?
(x/λ)x360(or 2pi)
What is reflection?
When a wave changes direction at a boundary between 2 different media, remaining in the original medium
What is the law of reflection?
The angle of incidence is equal to the angle of reflection
What wave properties remain the same after a wave has been reflected?
Frequency and wavelength
What are the 2 types of reflection?
Specular and Diffuse
What is specular reflection?
Occurs on smooth surfaces, where parallel rays reflect in a single direction
What is diffuse reflection?
Occurs on a rough surface, where parallel rays reflect in many directions
What is refraction?
When a wave changes direction as it changes speed when it passes from one medium to another.
If the wave slows down, it refracts …?
Towards the normal
If the wave speed up, it refracts …?
Away from the normal
What happens to the wavelength when the wave slows down
The wavelength decreases
What happens to the wavelength when the wave speeds up?
The wavelength increases
What is the refractive index(n)?
A measure of how much a material slows down light
What is the refractive index equation?
n=c/v
What is Snell’s Law?
n1sinθ1 = n2sinθ2
What happens when light enters a denser medium (n2>n1)?
Light bends towards the normal
What happens when light enters a less dense medium (n2<n1)?
Light bends away from the normal
What is the critical angle?
The angle of incidence at which the angle of reflection is 90 degrees.
What is the equation for the critical angle?
sinC = n2/n1
What are the conditions for total internal reflection?
When light travels from a medium with a higher refractive index to a medium with a lower refractive index, and the angle of incidence is greater than the critical angle
What is diffraction?
The spreading of waves when they pass through a gap/obstacle that is comparable in size to the wavelength of the wave
What wave properties are unchanged after diffraction occurs?
Speed, wavelength, frequency
What is a diffraction grating?
It consists of many closely spaced slits
What is produced from a diffraction grating?
It produces well defined interference patterns due to constructive interference
What are the 3 methods of polarisation?
Polarising filters, reflection and scattering
How do polarising filters polarise?
They only allow light oscillating in a specific plane to pass through
How does reflection cause polarisation?
Light reflected off a surface can become partially polarised
How does scattering cause polarisation?
Light scattered in the atmosphere becomes polarised
What is polarisation?
When the particles in a transverse wave can only oscillate along one direction only
What does it mean when a wave in partially polarised?
There are more waves oscillating in one particular plane but the wave is not completely plane polarised
What is an example of a circumstance where a wave becomes partially polarised?
When a wave reflects off a surface, like when light is reflected off water
Define the intensity of a progressive wave
The radiant power passing through a surface per unit area.
What is the equation for intensity?
I=P/A where P=radiant power and A=cross-sectional area
What is the units for Intensity?
Watts per metre squared
What is the relationship between Intensity and distance from the source?
I ∝ (1/r^2) due to the equation I = P/4πr^2
What is the relationship between intensity and amplitude?
Intensity ∝ (amplitude)^2
Are electromagnetic waves transverse or longitudinal?
Transverse
What is an electromagnetic wave?
Electric and magnetic fields oscillating at right angles to each other
What is the electromagnetic spectrum?
The full range of electromagnetic waves, which are classified by their wavelengths
List the electromagnetic spectrum, from highest wavelength to lowest wavelength
Radiowaves
Microwaves
Infrared
Visible Light
Ultraviolet
X rays
Gamma rays
What is the range of wavelengths for radiowaves?
10⁶-10^-1
What is the range of wavelengths of microwaves?
10^-1 to 10^-3
What is the range of wavelengths for infrared?
10^-3 to 7x10^-7
What is the range of wavelengths for Visible light?
7x10^-7 to 4x10^-7
What is the range of wavelengths for Ultraviolet?
4x10^-7 to 10^-8
What is the range of wavelengths for X-rays?
10^-8 to 10^-13
What is the range of wavelengths for Gamma rays?
10^-10 to 10^-16
What are the properties of electromagnetic waves?
They can be reflected, refracted and diffracted. They can be plane polarised. They all travel at the speed of light in vaccum
What is a use of the polarisation of electromagnetic waves?
In communications, in order to reduce interference between different transmitters
