Unit 4: Week 2 Flashcards
What is simple harmonic motion?
The periodic (repetitive motion) through an equilibrium. The restoring force is proportional to displacement- either side of the equilibrium is equal. The wave graph plotted from this is sinusoidal ( starts at 0)
Pendulum swing from pivot or mass bouncing on a spring
What is resonance/interference ?
When input frequency matches natural frequency resulting in a greater amplitude.
Interference is when 2 or more waves superimpose and produce a resultant wave of higher/lower amplitude.
Minimamaxima they cancel each other out- destructive interference
Maximamaxima amplitudes add together- constructive interference
What is Doppler shift?
When an object is moving towards you the distance decreases so the wave length also decreases causing frequency to increase. The difference between the reflected frequency and transmitted frequency is the doppler shifted frequency.
What is diffraction?
When a wave encounter a gap or object and spreads out past the edge.
The closer the wavelength is to the width of the gap the more diffraction occurs (doorframe vs sound saves)
The larger a wave length is the more it diffracts around an object (radio/microwaves around buildings)
What are interference patterns?
When one wave is emitted towards a double slit and act as two independent wave sources. They diffract and interfere, where there is constructive interference the bands are brighter due to increased amplitude. Where there is destructive interference the bands are dark due to waves cancelling each other out.
How do you make interference patters coherent?
For the interference pattern to be stable the waves must be coherent and have a constant phase difference (in and out of sync by the same amount). the wave must have the same frequency and wavelength. This is achieved using monochromatic light as it is the same colour and unidirectional. As opposed to incoherent LED lights which have different colours and omnidirectional
What is polarisation?
When EM waves- which are transverse and oscillate in many directions are restricted to one direction of oscillation- usually by using a filter. To filters perpendicular to each other block out all light.
Ariels pick up polarised signals- moving antenna helps
Reflected light is partially polarised in the horizontal plane
Some materials such as graphene can polarise waves (they have layers)
What is reflection? What are the two forms of reflection
When a ray changes direction after an interaction with a surface.
The angle of incidence=the angle of reflection- measured from the normal (perpendicular to surface)
The normal, incidence/reflected rays are in the same plane
Speculation reflection- when all the normals from each light ray are parallel. They hit a surface and a reflected uniformly- rays still in order
Diffused reflection- the normals from the incident rays are at different angles to each other and therefore reflect the rays in different orders
What are virtual images?
We perceive light to travel in straight lines due where we see an image we perceive light to have come from it resulting in a virtual ray and a virtual image, the light ray does not meet a corresponding object.
How are light rays reflected off a curved surface?
Curved surfaces can be seen as a collection of straight lines
Convex- the real rays don’t interact but the reflected rays can be extrapolated back as virtual rays to the focal point. A virtual images would be formed upright.
Concave- the real rays reflect and interact at the focal point in front of the mirror surface. This results in a real image which is upside down
What is refraction?
This is when light changes BOTH speed and direction when going form 1 medium to another.
The angle of approach is important as at a frontward angle the ray would slowdown but not change direction so this is not diffraction.
If you are going form more dense to less dense the light ray speeds up sooner on one side and is refracted away from the normal.
When looking into water the light is going form more to less dense so is refracted away but we perceive light to be coming in a straight line resulting in a virtual image directly above the actual object.
What is total internal reflection and what is it used in?
When a light ray is going form more to less dense the angle of reflection is larger than the angle of incidence. When the the angle of refraction reaches 90 this is the critical angle where light is still refracted. Beyond this the light ray undergoes total internal reflection.
Important in fiber optic cables–> core- high refractive index+ cladding-low refractive index
Used in endoscopes-
Light enters and is TIR and illuminates the target organ the diffuse reflection is sent back and is sent down the cope towards the eye
Binoculars- light rays interact with two prisms where it is TIR
