11 - Definitions Flashcards
Progressive wave
An oscillation that travels through matter. Transfers energy from one place to another
Transverse wave
Oscillations are perpendicular to the direction of energy. Has peaks and troughs where oscillator particles are at maximum displacement from their equilibrium position.
Displacement
Distance from equities position (m)
Amplitude
Maximum displacement from equilibrium position. (m)
Wavelength
Minimum distance between two points. e.g peaks or troughs.
Period of oscillation
Time taken for one oscillation or for a wave to move one whole wavelength past the given point.
Frequency
Number of wavelengths passing a given point per unit of time.
Wave speed
Distance travelled by the wave per second
Wave speed =
Frequency x wavelength
Frequency =
1 / period of the wave (S)
Phase difference
Difference between the displacement of particles along the wave, or the difference between the displacements of particles in different waves.
In phase
Phase difference of 0. In step with each other.
Anti-phase
Oscillating completely out of step with each other.
Phase difference equation
Distance between the waves or points
___________ X 360
Wavelength.
Law of reflection
Angle of incidence = angle of reflection
Refraction defined
Wave changes direction, as it changes speed passing though a different medium.
Refracts towards normal.
Refractive Index defined
Different materials refract light by different amounts. The angle the line in bent at depends on the relative speed of light through the material
Refractive index =
The speed of light in vacuum
__________________________
The speed of light though the material
Diffraction
When waves pass through a gap or travel around an obstacle, they spread out.
Speed, wavelength and frequency don’t change.
Occurred when gap is smaller than wavelength
Inverse Square - Intensity
Spread out equally
Total radiant power (P) at a distance (r) from the source is spread out over an area = to the surface area of a sphere.
I = P/ 4(pie)r^2
Polarisation
Only waves oscillating on one plane are able to get through filters.
Most naturally occurring EM waves are unpolarised, meaning they are oscillating on different planes.
Intensity is proportional to:
(Amplitude)^2
Longitudinal waves can’t be:
Plane polarised
Longitudinal wave
Wave oscillations are parallel to the direction of energy transfer.
Oscilloscope
Shows a graph of pd against time, of a signal.
Horizontal square represents specific time interval. = Time base
To get frequency use timebase to determine time period of the wave.
F=1/T
Total internal reflection
When the incidence angle is at the critical angle in a medium with a higher RI ,the ray will reflect back into the slow medium.
Higher the refractive index, the lower the critical angle
SinC = 1/n
Critical angle =
Refractive angle of 90 degrees,
So the light can’t escape the slower medium.
