C11 Waves 1 Flashcards
Define Progressive Wave
An oscillation that travels through a medium, transferring energy from one point to another, without permanently displacing any matter.
Define Transverse Wave, giving example
- A wave in which the oscillations or vibrations are perpendicular to the direction of energy transfer.
- S-waves, EM waves, water waves
Define Longitudinal Wave, giving example
- A wave in which the oscillations or vibrations are parallel to the direction of energy transfer.
- Often called compression waves, they are made of compressions and rarefactions.
- Regions of higher pressure and lower pressure air move, not particles.
- P-waves, sound waves
Formula of intensity of a wave
Radiant Power / Surface Area
I = P / A
What is phase difference
The difference between the displacement of particles along a wave, measured in degrees (360°) or radians (2π)
Antiphase
A phase difference of 180°, or π, where the max positive displacement of one wave is the max negative displacement of another.
What is reflection
A wave changes direction at a boundary between two different media, remaining in the original medium.
What is refraction
- A wave changes direction as it passes from one medium to another.
- There is always partial reflection when a wave refracts.
When do water waves refract, and what happens in shallower water.
- When there is a change in depth.
- When entering shallower water, waves slow down and wavelength shortens.
Why are optical microscope limited at a few hundred nanometres?
The diffraction of light as they pass through the apertures in the microscope cannot be avoided at a distance that small.
What affects how much diffraction occurs? When is it at its maximum?
- The relative sizes of the wavelength and the gap through which the wave passes through.
- The effect is strongest when the wavelength of the wave is roughly the same size as the gap.
What is partial polarisation
- It is when transverse waves reflect off a surface, e.g. light on water.
- There are more waves oscillating in one particular plane, with the water example it is horizontal polarisation.
Formula for intensity relating distance
I = P / 4πr^2
That is the surface area of a sphere, as the waves travels outward in all directions like a sphere.
Relationship between intensity and amplitude
Intensity is directly proportional to the amplitude^2
What is an EM wave?
Transverse waves, which can be thought of as electric and magnetic fields oscillating at right angles to each other.
Wavelengths of EM spectrum in metres
Radio: 10^6> to 0.1m
Microwave: 0.1m to 0.001
Infrared: 0.001m to 700nm
Visible: 700nm to 400nm
Ultaviolet: 400nm to 10^-8
X-rays: 10^-10 to 10^-13
Gamma Rays: 10^-13 to <10^-16
Wave equation for EM waves
c = fλ
As all EM waves travel at the speed of light in a vacuum.
Formula for refractive index
n = c / v
c = speed of light
v = speed of wave through material
How to calculate the angle at which light is refracted from one medium to another
n1 sinθ1 = n2 sinθ2
Refractive Index of Vacuum, Air, Water, Olive Oil, Crown Glass, Diamond
Vacuum & Air: 1.00
Water: 1.33
Olive Oil: 1.47
Crown Glass: 1.52
Diamond: 2.42
What is TIR (Total Internal Refraction)
- Diamond has a very high refractive index. Once light enters, it reflects internally multiple times before leaving.
- When light strikes the boundary at a large angle to the normal, it is totally internally reflected (no light is refracted out).
Conditions for TIR
- Light must be travelling through a medium with a higher refractive index than the material on the other side of the boundary.
- Angle at which light to the normal strikes must be > critical angle.
Calculating critical angle
sinC = 1 / n
