lenses work by refraction
light is refracted when it enters and leaves the lens
light is converged into an image
focal points
the focal point is where parallel rays are focused
the focal length is the distance between the centre of the lens and the focal point
eyesight correction
myopia (short-sightedness) is treated with diverging lenses
hyperopia (long-sightedness) is treated with converging lenses
sound is a longitudinal mechanical wave, caused by a vibrating object
it CANNOT travel through a vacuum
speed
distance/time = speed
volume of sound
higher amplitude, higher volume
higher frequency, higher pitch
visible white light is a spectrum
red, orange, yellow, green, blue, indigo, violet
transverse, non-mechanical waves
can travel through a vacuum
radio waves
lowest frequency, shortest wavelength
example: remote control
not dangerous
microwaves
cause water molecules to vibrate
when high-intensity, can heat human tissue
second-longest wavelength
infrared (IR) waves
example: thermal imaging
can cause burning of skin
can get trapped in greenhouse gases, causing global warming
ultraviolet (UV) waves
UV radiation causes suntans/sunburns
used in sterilization of instruments
ionising radiation (can cause cell mutation and skin cancer)
UVA: low energy, not very dangerous
UVB: high energy, causes sunburns & skin cancer
UVC: very dangerous, protected by the ozone layer
x-rays
can pass through soft tissue
absorbed by bone
this is why it’s used to detect injuries
ionising radiation (can cause cell mutation and cancer)
gamma waves
highest energy, highest frequency, shortest wavelength
emitted by radioactive materials
used in radiotherapy
highly penetrating
transverse
oscillation is at a right angle to the direction the wave is travelling in/energy transfer
if water wave hits surface, it’s reflected
reflection
mirrors reflect light
law of reflection - angle of incidence = angle of reflection
light rays reflect off most things
when luminous objects produce light, it reflects off non-luminous objects
refraction
light travels through transparent material, but not opaque material
when light travels through a transparent medium, it refracts