waves

make sure you can draw reflection and refraction diagrams. Also oscilloscope diagrams

define the term wave

a wave is a transfer of energy through a medium. It disrupts the medium (vibrations) but there is no net movement of matter

what are waves caused by?

an oscillating (vibrating) source

what can waves be used for?

to transfer information

what are the two types of waves?

longitudinal and transverse

what are longitudinal waves?

oscillations are parallel to the direction of energy transfer

what are transverse waves?

oscillations are at ninety degrees to the direction of energy transverse

define the term displacement (in terms of a displacement vs distance graph for a wave)

distance a particle has moved above or below its equilibrium/rest position

what does A stand for on the graph?

amplitude - maximum displacement (scalar)

what does λ mean on the graph?

wavelength - distance from a point on the wave to the next identical point

what does T means?

time period - time taken for one wave to pass a point

what does F mean on the graph?

frequency - the number of waves that pass a point in one second

what is the equation for frequency?

F=1/T

what is frequency measured in?

Hertz (Hz)

what is the formula for wave speed?

wave speed = wavelength x frequency

what are the three ways in which we can show waves?

diagram

ray

wavefronts

what are wave diagrams good for?

wavelength, time period, longitudinal/transverse, amplitude, displacement

what is showing waves as a ray good for?

direction (of energy transfer), change of direction

what is showing waves as wavefronts good for?

wavelength (calculate speed), direction, changes of direction

how can we measure speed of sound manually?

make a visible loud noise. At a measured distance away (eg end of a 100m track) start stopclock when motion is seen and stop it when sound is heart. Repeat and average.

how can we measure speed of sound with an oscilloscope?

measure distance between microphones (which are connected to an oscilloscope). Make noise near one microphone. Use timebase settings to find t. v=d/t

what remains constant in both reflection and refraction?

frequency

what is reflection?

a change in direction on a medium boundary

what is the law of reflection?

i=r

what is refraction?

when a wave changes its medium, speed changes

what happens when a wave hits at an angle to the normal from a fast→slow material?

bends towards the normal

what happens when a wave hits at an angle to the normal in a slow → fast material?

bends away from the normal

when does light travel fastest?

vaccuum - 3e8

what is the approximate range of visible light?

visible - red approx 700nm

• blue approx 400nm

what is the approximate wavelength of gamma?

10 to the power of -11 m

when does light travel slower?

in more optically dense materials

what is the speed of sound in air?

330 m/s

what is the audible range for humans?

20 Hz (infrasound) - 20000 Hz (ultrasound)

when does sound travel faster?

in more dense materials

what is the range of speed of water waves?

1-10m/s

when do water waves travel faster

deeper waters

what would you measure wavelength of water waves in

metres

what is the doppler effect?

when a source is moving, it can catch up or leave behind the waves it has already emitted.

catches up - wave fronts get closer - wavelength appears shorter - frequency appears higher

leaves behind - wave fronts spread out - wavelength appears longer - frequency appears lower

how do oscilloscopes work?

microphones convert sound waves into a voltage signal

oscilloscopes display the changing voltage

(treat oscilloscopes like digital graphs)

what type of wave is sound?

longitudinal

can sound refract

yes

can sound reflect

yes → echo

does sound have an amplitude

yes - volume (higher amplitude = louder sound)

does sound have a frequency

yes → pitch (higher frequency = higher pitch)