physics em waves

properties of EM waves

• travel through a vacuum

• travel at the same speed

• all transverse waves

• can be reflected, refracted, absorbed, transmitted, diffracted

• all transfer energy

in order of shortest to highest frequency

radio waves → microwaves → infrared radiation → visible light → ultraviolet → x-rays → gamma rays

wavelength and frequency are…

inversely proportional

wavefront definition

imaginary surface that representing points of wave that are the same time of their cycle

which EM wave can be detected by human eye

visible light

highest wavelength colour

red

highest frequency colour

violet

radio waves source; use+reason; harm

stars; broadcasting, telecommunication → can be reflected from earth’s atmosphere; no harm

microwaves source; use+reason; harm

stars; cooking, satellite communications → can penetrate earth’s atmosphere; internal heating of body tissue

infrared raditation source; use+reason; harm

stars; security, optical fibre communications (remotes) → can undergo total internal reflection; burns skin

visible light source; use+reason; harm

stars; photography → visible light rays refracting of object into eye; blindness

ultra violet source; use+reason; harm

stars (sun); detecting security ink → ink fluoresces with UV lighting; skin cancer 

x-rays source; use+reason; harm

.; to observe internal body conditions (x-ray) → can penetrate soft tissues but not bones; cancer

gamma rays source; use+reason; harm

.; sterilising food and medical equipment → can penetrate and kills cells ; cancer

what is more ionising

shorter wavelengths are more ionising

(NOT IN MOCKS) doppler effect

the apparent change of wavelength and frequency of a wave emitted by a moving source observed by an observer

(NOT IN MOCKS) doppler effect of stationary object

when a stationary object emits (sound) waves, waves are spread out symmetrically

higher frequency of sound waves…

higher pitch

(NOT IN MOCKS) when a police car is moving with its siren, what happens with the sound waves; doppler effect

the wavelength of the sound waves towards the direction of the car is shorter, with a higher frequency; the wavelength of sound waves behind the direction of the car is longer, with a longer frequency

frequency unit

Hz

wavelength unit

meters

wave speed unit

m/s

time and frequency equation

time(s)=1/fequency

amplitude

the distance from the undisturbed position to the peak/tough of wave

definition of wavelength

distance of a point in the wave to the same point in the next wave

longitudinal wave wavelength

centre of one compression to the next

transverse wave wavelength

one peak(crest) to the next peak

frequency definition

number of waves passing a point in a second

time period definition

time taken for a single wave to pass a point

transverse waves oscillations

vibrations are perpendicular to the direction of energy transfer

properties of transverse waves

• transfer energy, not particles

• mechanical waves, which travel solids and surface of liquids; not though liquids or gas

• electromagnetic waves, which travels through solids, liquids and gases through a vacuum

longitudinal waves oscillations

parallel to energy transfer

properties of longitudinal waves

• vibrate the same direction as wave travel

• transfers energy, but not matter

• can move through solids, liquids and gases

• can’t move through a vacuum

key features of longitudinal waves

• close vibrations : compression

• spaced vibrations : rarefraction