Physics (Unit 3: Waves) Flashcards
What are waves and what types are there?
Waves are a means of transferring energy without transferring matter. This is described as oscillation (repetitive fluctuations from side to side or as vibration upon a fixed positioon)
Explain compression and rarefraction?
- Features of a longitudinal wave affecting matter
- In compression, particles are brought closer together due to higher pressure
- In rarefraction, particles are brought furthur away due to lower pressure
Define the following terms:
- Peak/crest
- Dip/trough
- Equilibrium line
- Frequency:
- Time period
- Wavelength
- Amplitude
Crest: maximum height of a wave above the equilibrium line
Trough: minimum height of a wave below the equilibrium line
Equilibrium line: line in the middle of the wave that represent the level if it flattens out
Frequency: number of waves that pass a given point per second
Period: time it takes for a wave to complete one cycle
Wavelength: distance between one entire oscillation of that wave
Amplitude: maximum displacement point of a wave from the equilibrium line
Describe and compare electromagnetic and mechanical waves?
Electromagnetic:
- Only transverse
- Doesn’t require matter
- Can travel through a vacuum
- In case of light, higher amplitude means higher intensity
Mechanical:
- Either transverse or longitudinal
- Requires matter
- Can’t travel through vacuum
What are the formulae for measuring wave speed?
V=λf
V=Wave speed (m/s)
λ=Wavelength (m)
f=Frequency (Hz)
V=λ/T
T=Time period
What is the formula for measuring time period?
T=1/f
f=1/T
Explain reflection and its properties
- Refers to the change in direction of wave as a result of contact with something while staying in the same medium
- Angle of incidence is always equal to angle of reflection (i=r)
- Frequency, wavelength, and wave speed remain consistent
- Normal=imaginary line perpendicular to surface the wave comes in contact with
- Rough surfaces reflects the light in all directions
Explain diffraction and its properties
- The spreading out of waves as they go around an obstacle or through a gap
- The narrower the gap and the greater the wavelength, the more diffraction there is
- Frequency, wavelength, wave speed unchanged
- Gap width shorter than wavelength = reflection
- Gap width similar size to wavelength = diffraction
- Gap with larger than wavelength = most waves pass through; slight diffraction at edges
Explain refraction and its properties
- The redirection of a wave resulting from it entering a substance of different optical density
- Cause by ray of light entering substance at an agnle, causing different parts of the ray to speed/slow at different moments
- As the optical density increase, wave speed and wavelength decreases
- When ray enters more optically dense substance, it bends towards the normal
- In less optically dense substance, it bends away from the normal
Explain the refractive index and its relationship with angles of incidence and reflection
- Refractive index is the ratio of speed of light in a vacuum to speed of light in a particular medium
- n=c/v (c is speed of light in vacuum, v is speed of light in substance)
- Snell’s Law: n1xsin θ = n2 x sin θ2
- n = sin i/sin r
Briefly explain each type of EM wave
Radio waves:
Sources:
Oscillations in electrical circuits
Uses:
Telecommunications, TV, radio, bluetooth
Dangers:
None
Microwaves:
Sources:
Electronic circuits, cool objects
Uses:
Telecommunications, RADAR, cooking
Dangers:
Burns, cataracts
Infra-red waves:
Sources:
Electronic devices, warm objects
Uses:
Heating, cooking, TV remotes, night vision
Dangers:
Burns
Visible light waves:
Sources:
Sun, hot objects, electronic circuits
Uses:
Seeing, photos, transmitting data
Dangers:
Eye damage from bright lights
Ultraviolet waves:
Sources:
Sun, lamps, very hot objects
Uses:
Tanning salons, counterfeit detections, pollination, discos
Dangers:
Skin cancer
X-rays:
Sources:
Very fast electrons hitting a metal plate
Uses:
Meical imagery, security
Dangers:
Skin cancer
Gamma rays:
Sources:
Changes in atoms and their nuclei which leads to radioactive decay
Uses:
Cancer treatment, sterilizing hospital equipment, observing universe
Dangers:
Cancer
Order the following EM waves in ascending order of frequency and descending order of wavelength:
Ultraviolet waves
X-rays
Radio waves
Infra-red waves
Microwaves
Gamma rays
Visible light
Radio waves
Microwaves
Infra-red waves
Visible light waves
Ultraviolet waves
X-rays
Gamma rays
Describe the two types of lenses and their properties.
Lenses:
- Due to varying normals since lenses are curved, light refracts in a way that either converges or diverges it
Concave:
- Lens that bends inwards
- Light hits lens and refracts
- Lens is more optically dense so light moves towards the normal
- Causes light ray to diverge
- Images formed can be real or virtual
- Real images are made when the distance of object from centre of the lens is greater than the focal length; therefore they actually converge onto a position and can be projected onto a screen
- Virtual images are made when the distance of the object from the centre of the lens is less than the focal length; therefore they appear to have converged and cannot be projected onto a screen
Convex:
- Lens that bends outwards
- Light hits lens and refracts
- Lens is more optically dense so light moves towards the normal
- Causes light ray to converge towards a focal point
- Distance between middle line and focal point is called the focal length
- Images formed can be real or virtual
- Real images are made when the distance of object from centre of the lens is greater than the focal length; therefore they actually converge onto a position and can be projected onto a screen
- Image is inverted and magnified
- Virtual images are made when the distance of the object from the centre of the lens is less than the focal length; therefore they appear to have converged and cannot be projected onto a screen
- When seen from the right angle, it is upright and magnified
Note: rays that go through optical center continue straight forward
Describe the properties of light waves (different types of surfaces, colours, surfaces)
Opaque surfaces: no light transmitted
Transluscent: some light transmitted
Transparent: light transmitted
Colours:
Primary: red, blue, green
Secondary: magenta, cyan, yellow
Black: abscence of light
White: all colouors combined
All other colours: some combinatioon of each primary colour
Filters: only colour of filter passes through
Describe transverse and longitudinal waves.
Transverse: vibrations occur perpendicular to the direction energy is transferred.
Longitudinal: vibrations that occur in the same direction as the transfer of energy.
