Studied by 3 peopleis visible light longitudinal or transverse
transverse
can light be refracted
yes
can light be reflected
yes
sound waves
vibration of air molecules
are sound waves longitudinal or transverse
longitudinal
can sound waves be refracted
yes
can sound waves be reflected
yes
what are reflected sound waves called
echo
angle of incidence
angle of the wave approaching the boundary
angle of reflection
angle of wave leaving the boundary
law of reflection
angle of incidence = angle of reflection (i=r)
how are angles measured
between the wave direction and a line at 90 degrees to the boundary
where does the arrow of the incident ray point
towards the boundary
where does the arrow of the reflected ray point
away from the boundary
snell's law
n = sin i / sin r
what happens to light when it enters a denser medium
it bends towards the normal
which factor affects how much the light bends
density of the material
less dense to more dense medium
light bends towards the normal
more dense to less dense medium
light bends away from the normal
angle of incidence of light (notation)
i
angle of reflection of light (notation)
r
refractive index (notation)
n
relationship between refractive index, angle of incidence and angle of refraction
n = sin i / sin r
total internal reflection
when light is reflected when moving from a denser medium towards a less dense one
when does total internal reflection occur
when the angle of incidence is greater than the critical angle and the incident material is denser than the second material
two conditions for total internal reflection
angle of incidence > critical angle
incident material is denser than second material
where is total internal reflection utilised
optical fibres
prisms
total internal reflection - optical fibres
light travelling down an optical fibre is totally internally reflected each time it hits the edge of the fibre
total internal reflection - where is it used along optical fibres
communications
endoscopes
decorative lamps
safety reflectors
total internal reflection - prisms
the light totally internally reflects in both prisms
total internal reflection - where is it used along prisms
periscopes
binoculars
telescopes
cameras
periscope
a device that can be used to see over tall objects consisting of two right-angled prisms
what happens to the angle of incidence once the angle of refraction is exactly 90
it's known as the critical angle
angle of incidence larger than critical angle
refracted ray is reflected
relationship between critical angle and refractive index
sin c = 1/nl
large refractive index of a material
small critical angle
frequency range for human hearing
20 - 20000 Hz
what can be observed by an oscilloscope
changing signals like sound waves and alternating current
what happens to the longitudinal sound wave when a microphone is connected to an oscilloscope
it is displayed as though a transverse wave on the screen
what does the time base measure
time period of the wavew
what does the height of the wave measured from the centre of the screen tell us
amplitude
what does the number of waves on the screen tell us
frequency
more waves displayed
increased frequency
less waves displayed
decreased frequency
high pitch
high frequency of vibrationl
low pitch
low frequency of vibration
loud sound
large amplitude
soft sound
small amplitude
investigating refraction - variables
independent variable: shape of block dependent variable: direction of refraction control variables: width and frequency of light
investigating refraction - equipment
ray box
protractor
paper
pencil
ruler
perspex blocks
investigating refraction - method
place glass box on a sheet of paper
draw around rectangular perspex
direct a beam of light at the face of the box using the ray box
mark the paper
draw a dashed line at right angles to the outline of the block where the points are
remove block and join marked points
replace block with outline and repeat at a different angle
repeat for each shape of perspex block
investigating refraction - marking the paper
point on the ray
point where the ray enters
point where the ray exits
point on the exit light ray
investigating refraction - refraction patterns for different blocks
investigating refraction - analysis
i and r are measured from normal
investigating refraction - systematic errors
incorrectly drawn lines
investigating refraction - random errors
inaccurately marked points
protactor resolution
investigating refraction - safety considerations
ray box light could cause burns
light might damage eye
keep all liquids away
investigating refractive index - variables
independent variable: angle of incidence dependent variable: angle of refraction control variables: use of perspex block, width and frequency of light beam
investigating refractive index - method
same as investigating refraction
investigating refractive index - method
same as investigating refraction
investigating refractive index - analysis
n = sin i / sin r
investigating refractive index - systematic errors, safety consideration
same as investigating refraction
investigating the speed of sound - equipment
trundle wheel
wooden blocks
stopwatch
oscilloscope
microphones
tape measure
investigating the speed of sound - measuring the speed of sound between two points (variables)
independent variable: distance dependent variable: time control variable: same location
investigating the speed of sound - measuring the speed of sound between two points (method)
measure distance between 2 people
1 person should hold two wooden blocks to bang together above their head
the other should hold a stopwatch which they start when they see the blocks bang together and stop when they hear it
repeat for average
repeat with various distances
investigating the speed of sound - measuring the speed of sound between two points (analysis)
speed = distance / time
investigating the speed of sound - measuring the speed of sound with oscilloscopes (variables)
independent variable: distance dependent variable: time control variables: same location, same set of microphones
investigating the speed of sound - measuring the speed of sound with oscilloscopes (method)
connect two microphones to an oscilloscope and place them 2 m
set up the oscilloscope so that it triggers when the first microphone detects a sound and adjust the time base so that the sound arriving at both microphones can be seen on the screen
make a large clap using the two wooden blocks next to the first microphone and use the oscilloscope to determine the time at which the clap reaches each microphone and the time difference between them
repeat at several distances
investigating the speed of sound - measuring the speed of sound with oscilloscopes (analysis)
speed = distance / time
using an oscilloscope - variables
independent variables: tuning forks of different frequencies dependent variable: time period
using an oscilloscope - equipment
tuning forks
microphone
oscilloscope
wires
using an oscilloscope - method
connect the microphone to the oscilloscope and test it
adjust the time base of the oscilloscope until the signal fits on the screen
strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
freeze the image on the oscilloscope screen
measure and record the time period of the wave signal on the screen
repeat for varying tuning forks
using an oscilloscope - analysis
frequency = 1 / time period
Note
Flashcard