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physics test - y9

lenses

  • 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

  • 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

light

  • 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

water waves

  • 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 & refraction

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