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