Teaching Oscillations
And Waves with Confidence
I.O.P day
@
Rugby School
2015
By
Dr Andy Davies (Head of Physics, Rugby School)
Sue Haslam (Physics Technician, Rugby School)
Dr David Lo (Senior Physics Technician, Rugby School)
David Wan (Physics Technician, Rugby School)
Refraction Frog Demo
Experiment instructions:You will find the apparatus as in the picture.
Slowly fill the black bucket containing the frog with water, watch the computer screen
and see frog appear, and reverse, if you empty the water out the frog will disappear.
Safety notes:Please DO NOT attempt to move the camera attached to the bucket.
Digital – Analogue Radios
Experiment instructions:You will find the two radios side by side, turn both radios on
to a reasonable volume making sure that they are both tuned in to the same station. Quickly
turn the volume down on the analogue radio and listen for the time delay, usually around
3secs difference. The time lag of digital is due to the time taken to regenerate the digital
signals when removing noise from the signal.
The main difference between analogy and digital signals is that an analogue signal is
continuous and a digital signal is discrete. Analogue technologies record waveforms as they
are, while digital technologies convert analogue signals into numbers. Digital
communication systems offer much more efficiency, better performance, and much greater
flexibility than analogue.
Safety notes:Please ensure to turn both radios off when finished with the apparatus.
Standing Waves in Air Column:
Determining the Speed of Sound
Experiment instructions:Here we have a Standing wave using a sound speaker
connected to a pipe which is open each end, connected to a Signal generator in a column of
water.You can determine when you have a standing wave, by adjusting the length of the
pipe, pull the pipe up and down in the column until you hear the loudest tone. This will be
your Standing wave as the pipe was the right length for the frequency set on the Signal
Generator.
Fundamental wave, to determine the Speed of Sound.
Maximum Signal
Length of pipe
1
4
Wave Length
400Hz
Example:L 21 = 0.21m
𝜆
= 0.21
4
= 0.21
λ= 0.84
f = 400Hz
V = f λ = 400 x 0.84
= 336ms -1
Safety notes:-Please ensure to turn the signal generator off after use.
Fluorescein/Water and Light source
Experiment instructions:Turn the power to the light source on, use the bar on the lamp
to rotate the light source until you have visible beams. Ideally this is best in a darkened
room, so that you can see the beam better. Depending on the angle of incidence with the
water surface, refraction or total internal reflection can be observed.
Using a protractor it is possible to estimate the critical angle at which total internal reflection
begins to occur.
Safety notes:Please ensure to turn the light source off after use as it becomes very hot and
will melt glued seal.
Optic fibre demo with water
Experiment instructions:The equipment will be set up as in the picture. Ensure that
there is enough water in the demijohn to enable a good flow through the spout. Turn on the
laser by pressing the button at the rear of the pen, remove plug from the spout of the
demijohn and ensure that the laser is angled so that the beam lines up with the spout outlet.
The beam of the laser should bend with the water flow.
This experiment works better in a darkened room. A wonderful demonstration of the total
internal reflection of light, a jet of water 'traps' light, just like an optical fibre
Safety notes:Please take care when using the laser, DO NOT look directly into the light.
Pendulum Wave
Experiment instructions:Turn on the light source by pressing the button at the top of the lamp once, this will show a
shadow of the wave at the opposite end. Lift the hinged wooden bar and rest all the coloured
balls across it, gently release the balls by dropping the down the hinged bar. Observe the
wave patterns.
The main idea of a pendulum wave is to observe how once the pendulums of different
lengths are released, they immediately have different frequencies. From our studies of
simple harmonic motion, the pendulum wave is made up of many pendulums that are
undergoing simple harmonic motion. We know that the period and the frequency is not
affected by the mass of the balls. What each wave is affected by is the length of the string
from which each ball is hanging. This is why the frequency of each pendulum is different
than the one next to it.
String Length:




the length represents the wavelength of the pendulum
the lengths will be found using a recursive formula
the first length will be determined using a chosen frequency
the length of each pendulum includes the start of the string to the center of mass of
the ball
Frequency:



the number of waves that pass a point in one second
it is controlled by the wavelength (the length of the string)
the number of oscillations needs to be chosen in order to then use a recursive
formula to calculate the lengths of each
The first frequency will be determined by dividing the number of chosen back and forth
swings in 30 seconds by 30.
Pendulum Wave continued…
Formulas:


formula for a pendulum is solved for the period of each pendulum
once the frequency is determined, then a recursive can be created to solve for the remaining
lengths.
Angles:



the balls should be released at an angle of 45 degrees with the release mechanism
this will allow all the pendulums to be released simultaneously
the different frequencies will be observed immediately when released properly
Release Mechanism:

this is needed so that all the balls are released at the same time and the same angle
recommended
that it be a flat board
Safety notes:Please ensure that you turn off the light source after use
Bedstead wave machine
Experiment instructions:Transverse Waves:
The wave machine is a very simple device used to show what transverse waves look
like. It has many long wooden dowels connected by a thin wire. When you move the dowels on the
end, it transmits energy to the other dowels through the wire.
This wave is also similar to the wave you do at sporting events. Instead of people moving up and
down, we have wooden dowels moving up and down. In both cases, energy is transmitted in the form
of a wave. A sound wave is similar to this, but in a sound wave the movement is back and forth
instead of up and down.
Safety notes:-
Ruben’s Tube
Experiment instructions:The “Rubens “tube gets its name from a German physicist,
Heinrich Rubens, who first developed the experiment in 1904.
You can use both a speaker and a musical keyboard with a Signal generator. (To switch
from one to the other see the picture below) At the correct frequency, the speaker sets up a
standing wave within the tube. At the nodes of the wave, the gas pressure remains constant,
whilst at the antinodes, the change in pressure is at its greatest. (This is shown by the red
dotted arrows in the diagram below)
When we play music through the tube we can see the tune. This is because the different
notes with different frequencies set up different standing wave patterns.
Flick switch down for External
audio input. (Keyboard)
Safety notes:Please take care when using the Ruben’s tube due to naked flames and the tube will become
extremely HOT.
Ruben’s Tube continued……
When the loudspeaker vibrates it sends a series of waves of air down the tube at the speed of
sound, these then reflect off the far end of the tube, so there are two sets of waves moving
through the tube in opposite directions.
For most wavelengths this does not produce a very interesting effect, but when the length of
the tube is a multiple of half the wavelength the two waves add together to form what is
known as a standing wave. In some places the two waves add together forming extra-large
changes in pressure (antinodes) and in other areas they cancel each other out so the pressure
is constant (nodes).
The loudspeaker vibrates creating
compressions in the air which move down the
tube (sound waves)
When they hit the end they reflect back, and
travel back again. So you have two waves
moving in opposite directions inside the tube.
If the wavelength is right the two waves will add
together to form a stationary pattern called a
standing wave. This contains areas where
the pressure is varying by a large amount
(antinodes) and others where it is constant
(nodes)
How does this standing wave affect the flames?
That is in fact a very good question, the average pressure at all points of the tube is the same,
so the answer is not that some parts of the wave are at a higher pressure than others. This
means the answer must lie with how the flames react to the changes in pressure.
Just to make things more complex Rubens actually discovered that his tube could behave in
two completely opposite ways. When the sound is relatively quiet the flames get shorter at
the antinodes but when the sound is very loud they get longer.
At the start of this the flames near (but not quite at) the ends are being shortened by the
sound, but as the sound gets louder the flames get longer
These two completely different behaviours seem to have different causes.
Ruben’s Tube continued……
Relatively quiet
When the sound is relatively quiet the changes in pressure due to the sound are less than the gas
pressure. For relatively small pressure differences the flow of gas through a hole is proportional to the
square root of the pressure difference (pressure difference is energy per unit volume of gas, and the
change in kinetic energy of the gas is proportional to its velocity squared, so the velocity and so the
flow rate is proportional to the square root of the pressure difference).
This relationship means that the increase in flow when the pressure increases is less than the decrease
in flow when the pressure decreases so on average the flow, and therefore the flame length, is less
where the pressure is varying a lot, at the antinodes.
The flame on the left has a constant pressure, the pressure for the flame on the right is changing
When the pressure increases the flow of gas
increases a bit and the flame gets slightly longer.
When the pressure decreases the flow reduces a
lot and the flame gets a lot smaller.
This means that the flames are shorter at the antinodes (loud parts of the tube) and the same length at
the nodes.
In this case the areas with the largest
changes in pressure produce shorter
flames and those where it is quiet will
produce longer ones
When the sound is very loud
I have not found any discussion of this case, Rubens seemed to think that it was so obvious that he
didn't bother writing it down. It isn't obvious to me, but this is what I can work out:
When the speaker is set to loud the changes in pressure due to the sound are much larger than the gas
pressure, and the behaviour is very different. Now the gas is squirted out of the holes and forms a jet
traveling away from the tube.
The pressure then becomes lower in the tube than outside so gasses from outside are sucked in.
However these gasses are not just the propane that was squirted out; suction doesn't have a direction,
so gases are sucked in from all around the holes, most of which are air.
Ruben’s Tube continued……
The flame on the left has a constant pressure, the pressure for the flame on the right is changing
stop burning.
The pressure
difference is very
large so gas is
squirted out forming
a fast moving jet
The pressure change is so
large that air is actually
sucked in. Because suction
happens in all directions, most
of what gets sucked in is air.
So to start with lots of gas is
squirted out and air is sucked
back in.
After a while however the gas
around the antinodes gets
thoroughly mixed with air, and
the flames become very well
oxygenated and blue. If it is
left long enough they can
even
The areas with the loudest sound have the So gas is squirted out and air is sucked in allowing more
gas to be squirted out in the next cycle. This hugely increases the flow of gas out of the tube, for a
while... the mixture of gases in the tube is slowly made up of more and more air. This makes the
burning cleaner and cleaner, forming a bluer flame, until eventually there isn't enough gas to sustain
combustion and it can put itself out. longest flames
Over time air is sucked in making the gas mixture weaker and
weaker. Leaving the antinodes with very little gas to squirt out.
Rijke Tube
Rijke's tube turns heat into sound, by creating a self-amplifying standing wave. It is an
entertaining phenomenon in acoustics and is an excellent example of resonance.
Experiment instructions:Light the Bunsen burner and set onto the hottest flame by
opening the air hole on the bottom of the Bunsen’s collar, using the heat gloves provided
place the Rijke tube over the flame until the gauze begins to glow. Lift the tube up and away
from the Bunsen flame (you should by now hear the tube “Singing”) as the tube is at its
resonance frequency, ( causing a standing wave inside the tube) although the resonance does
not occur if tipped on its side but does return if the tube is placed back vertical. The
resonance also does not occur if turned upside down.
Safety notes:Please wear heat proof gloves provided as tube will become extremely hot
Rijke Tube
Mechanism (Ripped unashamedly from wikipedia!)
The sound comes from a standing wave whose wavelength is about twice the length of the
tube, giving the fundamental frequency. Lord Rayleigh, in his book, gave the correct
explanation of how the sound is stimulated. The flow of air past the gauze is a combination of
two motions. There is a uniform upwards motion of the air due to a convection current
resulting from the gauze heating up the air. Superimposed on this is the motion due to the
sound wave.
For half the vibration cycle, the air flows into the tube from both ends until the pressure
reaches a maximum. During the other half cycle, the flow of air is outwards until the
minimum pressure is reached. All air flowing past the gauze is heated to the temperature of
the gauze and any transfer of heat to the air will increase its pressure according to the gas
law. As the air flows upwards past the gauze most of it will already be hot because it has just
come downwards past the gauze during the previous half cycle. However, just before the
pressure maximum, a small quantity of cool air comes into contact with the gauze and its
pressure is suddenly increased. This increases the pressure maximum, so reinforcing the
vibration. During the other half cycle, when the pressure is decreasing, the air above the
gauze is forced downwards past the gauze again. Since it is already hot, no pressure change
due to the gauze takes place, since there is no transfer of heat. The sound wave is therefore
reinforced once every vibration cycle, and it quickly builds up to a very large amplitude.
This explains why there is no sound when the flame is heating the gauze: all air flowing
through the tube is heated by the flame, so when it reaches the gauze, it is already hot and no
pressure increase takes place.
When the gauze is in the upper half of the tube, there is no sound. In this case, the cool air
brought in from the bottom by the convection current reaches the gauze towards the end of
the outward vibration movement. This is immediately before the pressure minimum, so a
sudden increase in pressure due to the heat transfer tends to cancel out the sound wave
instead of reinforcing it.
The position of the gauze in the tube is not critical as long as it is in the lower half. To work
out its best position, there are two things to consider. Most heat will be transferred to the air
where the displacement of the wave is a maximum, i.e. at the end of the tube. However, the
effect of increasing the pressure is greatest where there is the greatest pressure variation, i.e.
in the middle of the tube. Placing the gauze midway between these two positions (one quarter
of the way in from the bottom end) is a simple way to come close to the optimal placement.
The Rijke tube is considered to be a standing wave form of thermoacoustic devices known as
"heat engines" or "prime movers".
Resonance of a Wine Glass
Experiment instructions:Turn on the Signal generator and adjust the frequency setting,
the drinking straw in the wine glass will “dance” when the resonance frequency is reached.
A glass has a natural resonance. Resonance is the natural frequency at which the glass will
readily vibrate. To find the resonance of the glass, ping the glass and listen to the sound. That is
the correct frequency (or tone) for the glass to start to vibrate.
The glass itself must not be affected by damping. Damping is interference with a force which will
act to prevent the glass from vibrating. Embossed glasses should be avoided. Lead in lead crystal
may provide damping although otherwise the glass is very pure. The glass should be empty.
A wine glass is a good shape because it stands on a stem. This reduces the amount of damping
that could be caused by a glass sitting directly on a surface such as a pint glass. The walls of the
glass should be as thin as possible.
Making the same tone as the natural frequency of the glass will induce vibration in the glass.
However, the note alone is not the only factor - volume is also important. The louder the sound,
the more violent the vibrations will be. When they reach a level that the glass cannot withstand it
will shatter.
The volume required is more than 100 db. A level that is difficult but not impossible to reach
with just the voice (examples of glasses being smashed by the human voice can be found on
youtube). Normal speech is around 50 db. In experiments, often an amplifier and speaker are used
so achieve the required volume.
Safety notes: - Please ensure to wear safety glasses provided, and do not leave signal
generator on for too long as it may damage eardrums.
Forced Vibrations and Resonance
Experiment instructions:Firstly for this experiment you will need to turn on the signal generator.
At most frequencies the mass on the spring oscillates gently, but at resonant frequency
(Indicated in the picture of SG) the vibration is violent.
Alter the frequency of the forcing vibrations by adjusting the SG
The Perspex tube prevents the “Pendulum” mode of oscillation.
A scale in the background enables a graph of amplitude against frequency to be made.
Resonance frequency
Safety notes:Please ensure to turn off the Signal generator.
Resonance of hacksaw blade projected
onto a screen using
a torch
Experiment instructions:You will find the apparatus set up as in the picture. Switch on
the Signal generator, then the light source by pressing the button at the top of the torch
once.You can then adjust the frequency by turning the dial on the Signal generator. Then
observe the behaviour of the hacksaw blade. When the driving frequency matches the
natural frequency of an oscillator the amplitude of oscillation can rise dramatically. This is
resonance. This experiment gets you to measure how the amplitude of an oscillating
hacksaw blade changes with the frequency of the driver. The hacksaw blade is linked to the
vibration generator by a piece of cord. You will see the blade oscillate but will have to
decide how to measure the amplitude of oscillation.
Torch
Hacksaw blade
Signal
generator
Vibrating generator
Safety notes:-Please ensure to switch the SG and the torch off after use (torch will need to
be pressed three times)
Alien Mass
Experiment instructions:Students vary mass and measure the time period of oscillation of the hacksaw blade. A
calibration chart is drawn and then the unknown mass of the alien is determined from the
graph. They can finally check the accuracy of their result using a mass balance.
The equipment for this experiment is laid out on the bench in front of you. Also on the
opposite page, there is a worksheet to fill out if you would like to have a go at “finding the
mass of the Alien”
Safety notes:Take care when using the hacksaw oscillator especially when loaded
with masses.
Alien Mass
Ripple Tank
Experiment instructions:The ripple tank is already set up and levelled for you to use,
plug the other lead into the battery pack that runs the motor, and turn on the lamp (switch at
the front ) of the overhead projector. You can adjust the waves by speeding up or slowing
down the motor. With the ripple tank you will find a basket of accessories (feel free to use
them) to encounter different wave formations.
Safety notes
Please ensure to turn off the lamp on the overhead projector and unplug one lead to the
motor.
Ripple Tank continued…
Observing Refraction:
The waves travel more slowly in shallow water because of friction with the bottom.
With the glass edge parallel to the vibrating beam, students should notice that the wave speed
is
reduced
and
wavelength
becomes
smaller
as
waves
cross
the
boundary.
With the glass edge at various angles to the incoming waves, students should notice that the
waves change direction as they cross the boundary.
Practical Guidance
The tank and the glass plate need to be very clean and free from grease.
To get sufficient change in wave speed at the boundary with the glass:

Make the water on top of the glass very shallow.

Pour water into the tank until it just covers the glass and then drain off a little of it. It
may be necessary to re-level the tank to ensure that the film doesn’t break up into
puddles.

Use a low frequency, long wavelength (about 10 rev / second).
To get sharp waves, adjust the height of the vibrator so that it is just below the mean water
level. The vibrator should just ‘hold up a film of water’ when it is still.
This simple stroboscope enables students to 'freeze' repetitive motions – or to slow them
down for closer study. For example, continuous ripples are easier to see by using a
stroboscope, especially those ripples with higher frequencies.
Pepper’s Ghost
Experiment instructions:The apparatus is ready for you to use.
Using the small grey remote control provided, switch on the background (picture of chairs
and table in garden) by pressing Number 1 on .To make the ghost appear in the picture
(next to the chair) press Number 2 on. Pepper's ghost is an illusion technique used in theatre,
haunted houses, dark rides and in some magic tricks. Using plate glass, Plexiglas or plastic film and
special lighting techniques, it can make objects seem to appear or disappear, to become
transparent, or to make one object morph into another. It is named after John Henry Pepper, who
popularized the effect.
Hole where the camera is placed.
Image of the ghost
View of the inside of the box
Safety notes:-Please ensure that you turn the apparatus off, by pressing Number 2 off and
Number 1 off on the small grey remote control.
Pepper’s Ghost continued..
How Does It Work ?
The following question from the IGCSE Edexcel paper 1 from Jan 2014 assessed Pepper’s
Ghost:
Disappearing beaker
Experiment instructions:You will find a beaker on the bench like the one in the
picture. Using the tongs provided lift the inner beaker up and see it appear.
Glass objects are visible because they reflect some of the light that shines on them and bend
or refract the light that shines through them. If you eliminate reflection from and refraction
by a glass object, you can make that object disappear.
This is achieved by using oil and pyrex glass which have almost identical refractive indices.
Safety notes:Please do not take the small inner beaker out fully due to the oil.
Polymer Beads
Experiment instructions:Look into the mixing bowl, take the draining spoon and place
it into the water, gentle using a scooping action look at the polymer beads.
The reason for the beads appearing invisible is because the water and the beads have the
same refractive index as each other, (bending the light in the same way)
Polymer beads on draining spoon
Safety notes:Please do not eat the beads.
Measuring Speed of sound with a
Scaler timer
Experiment instructions:The apparatus will be as in the picture, switch on the Scaler
timer. Holding the round weight in one hand and the hammer in the other, tap the weight
with the hammer alongside the speaker on the left. Do not strike the weight when on the
bench, as this will give a false result.
The speed of sound is the distance travelled per unit of time
by a sound wave propagating through an elastic medium. In dry air at 20 °C, at sea level, the
speed of sound is 343 metres per second. Now repeat the experiment by placing the weight
on the bench and hitting it with the hammer – you will get the speed of sound through the
solid bench.
Safety notes:Please mind your fingers when striking the weight with the hammer.
Standing Wave on String
Experiment instructions:The apparatus will be set up as in the picture. Turn the power to the
Signal generator on, you may adjust the dial on the Signal generator to observe the different
wave formations using different frequencies. A strobe can be used to freeze the wave. In
physics a standing wave – also known as a stationary wave – is a wave that remains in a
constant position.
Safety notes:Please take care when using the strobe as flashing lights may cause dizziness.
(Do not use if you suffer from epilepsy).
Loudspeaker - Candle
Experiment instructions:You will find the apparatus as in the pictures.
Light the candle with the matches provided, turn on the signal generator, and adjust the
frequency dial on the signal generator to observe the behaviour of the flame as you change
the frequency.
The motion of a candle flame in front of a loudspeaker has been suggested as a productive
demonstration of the longitudinal wave nature of sound.
Safety notes:Please turn off the signal generator and distinguish the candle when
finished with the apparatus.
Superposition using sound waves and
microphone - CRO
Experiment instructions:Turn on the CRO (this will have set to the required frequency)
ensure that the microphone is also on, and then the Signal generator. Move the microphone
from one side to another between the speakers (you should hear the Max and Min where the
Fringes are formed from the speakers.
Coherent source (signal generator)
A / B (speakers)
X
(microphone)
Path difference = AX – B X
= n λ for maxima
A wave form is made up of a
node and anti-node. The node is
where the wave doesn't move, the
anti-node is the point halfway
between two nodes, it is where
the wave moved the most.
Superposition using sound waves and
microphone – CRO Continued…
Coherent source (signal generator)
A / B (speakers)
X (microphone)
AX – BX = n λ
Fringes are shown in this diagram
(Min and Max)
The signal generator drives the two loudspeakers, connected in parallel, which are at each
end of a metre rule. Connect the microphone, to the CRO which is switched to its most
sensitive range, and put it opposite the point midway between the two loudspeakers, that
is at the central maximum. The CRO has already been set to the frequency needed for use
in the room.
Each loudspeaker contributes half the total amplitude.
The Oscilloscope trace indicates potential differences. When both speakers are emitting
the potential difference is doubled.
Energy is not created or destroyed when two waves superpose, it is just distributed
differently, being proportional to the square of the amplitude of the resulting wave at each
point.
The microphone detects amplitude, as do aerials and radio receivers.
Safety notes:Please ensure to turn off the Signal generator after use.
Diffraction of a microwave
Experiment instructions:Begin with the two metal plates together, Turn the power supply and the amplifier on ,
gently pull the plates apart to see the max signal , when gap size is equal to the wave length
of the 2.8cm microwave, beyond this gap size the signal decreases and there is less
diffraction.
Safety notes:Please ensure to turn off the power supply and the amplifier
Rotating Microwave CD model
To illustrate how a laser reads off the digital information from the surface of a CD/DVD we
can use the much larger wavelengths of microwaves and scale up our surface accordingly!
Experiment instructions:The apparatus has already been set up for you to use.
Turn the power supply on and then the amplifier, gentle spin the CD model disc, carefully
listen as the disc spins to hear the frequency wave form which is being generated by the CD
disc.
PSU: On/Off
Amplifier: On /off
Volume
Microwave transmitter and
receiver
Safety notes:Please ensure to turn both the Power supply and the amplifier off after use.
Rotating Microwave CD model
Continued..
How the Laser Reads Data on the CD
CD Laser Reads Bumps (Pits Inverted) and Lands,
both of which have reflective metal surfaces. The photodetector
receives no signal from bumps, only from lands, due to destructive
interference of light waves. The clever bit is to make the bumps exactly one
quarter of the wavelength of the laser light!
Destructive Interference of Light Waves. The destructive interference
of light waves reflected by the bump and land occurs due to the depth of the pits
being precisely 1/4 wavelength of the laser - thus, the distance the laser beam travels
from laser to photodetector is 1/2 wavelength longer for lands than for bumps.
The laser beamwidth is slightly wider than a bump so it always illuminates the
adjacent land whenever it illuminates a bump; consequently, bumps always appear
dark to the photodetector due to destructive interference of the light waves.
Chladni Plates
Experiment instructions:The apparatus is already set-up for you to use.
Turn on the power to the Signal generator.
Turn the frequency dial to find the different patterns on the plate.
You may add more sand to the plate if necessary, using it sparingly.
Chladni patterns can also be formed by using circular or rectangular metal plates on a
mechanical driver controlled by a signal generator. This method avoids having to practice
your bowing. The patterns are now different since they have antinodes at the centre (which
is being vibrated) rather than nodes with the centre rigidly attached and the edge bowed.
Input /output
Frequency
Safety notes:Please turn off the power to the Signal generator after you have finished
with the apparatus.
Standing Waves using UHF
Oscillator
Experiment instructions:This apparatus is all set-up and ready for you to use.
Gently push the trolley manually, up and down the track, as the cart moves along the rails you will
see the maxima and minima on the edspot galvanometer.
You may have seen that
1.
A 1 GHz transmitter can set up stationary wave patterns.
2.
The distance between two adjacent nodes is about 15 cm.
3.
The wavelength of the radiation is about 30 cm.
This is less easy to do than other standing wave demonstrations. With care it can yield pleasing
results. It should, if used, be given to students with sufficient patience and skill to produce clear
results.
Marks have been drawn on the top of the guide rails (as seen in picture) to show the maxima.
A determination of the speed of the radio waves can be made:
Speed of wave = F x Wave length
Frequency = 1 x 109Hz
Wave length = 2 x distance between the maxima
2 x distance of maxima is approximately 30cm, which is equal to 0.3m
(0.3 x 109 = 300,000m)
Superposition using UHF Oscillator
continued
Marks drawn on the rails for
maxima.
Safety notes:Please do not move the Edspot Galvanometer whilst switched on.
Diffraction Grating and Fog Machine
Experiment instructions:Switch on the fog machine at the back of the machine, and
wait for the green light to stay on, then press the green push button to generate fog (but
please do not over do the fog as the room soon fills with fog). Turn the laser pointers on by
turning the dials on the top of the pointers clockwise (see picture below).Observe the fringes
projected onto the wall.
A diffraction grating is an optical component with a periodic structure, which splits and diffracts
light into several beams travelling in different directions. The directions of these beams depend on
the spacing of the grating and the wavelength of the light so that the grating acts as the dispersive
element. Because of this, gratings are commonly used in monochrometers and spectrometers.
Diffraction Gratings
To turn the leaser pointers on twist
the dial shown in the picture
clockwise.
Diffraction Grating and Fog machine
continued…
View projected onto the wall of the
fringes.
Beams from the laser pointer shown
by the fog.
The fog enables the diffracted beams to be observed, rather than simply the projected fringes
and you can illustrate the spacing difference for reed and green laser light.
Diffraction Grating and Fog Machine
continued…
Fogger
On / off switch
Green light must be on (not flashing)
before use, then press the green push
switch to generate fog.
Safety notes:-Warning do not look directly into the beam of the laser! Please ensure to
turn the laser pointers and the fog machine off after use.
Dispersion and Colour
Experiment instructions:In front of you is the apparatus as in the picture. Turn the ray
box light source on, using the Power supply. Coloured filters can be used with the mirrors
on the ray box to mix the 3 primary colours to give white light. The 2 glass prism can be
used to disperse the white light and then recombine it to produce white light. The infra-red
detector can be used to demonstrate infra-red beyond the red part of the visible spectrum.
Safety notes:Please ensure that you turn the light source off after use.
Prism experiment. Isaac Newton's diagram of an experiment on light with two prisms. From a
letter to the Royal Society, 6th June 1672. © The Royal Society
Diffraction of light using an
adjustable slit
Experiment instructions:Turn on the power supply to the light source sitting on a
yellow upturned box. Look through the slits on the bench towards the light source. By
adjusting the slit, it is possible to see diffraction of visible light source.
Light source
Power supply
Adjust slit here
Safety notes:Please ensure to turn off the power supply to the light source.
Barton’s Pendulum
Experiment instructions:This classic demonstration shows the effects of resonance (and non-resonance). Draw attention to the
initial transient oscillations that die away. Bring out the point that the pendulums then all oscillate at
the driving frequency, but the ‘resonant’ pendulum oscillates with the greatest amplitude. As an
extension, you can also illustrate how damping affects resonance. Weight each paper cone, (e.g. with
a plastic or metal ring, such as a curtain ring), so that it is less affected by air resistance. The
transient oscillations take longer to die away, and when the ‘steady state’ is reached the amplitude of
the resonant pendulum is larger.
Can you spot the phase difference between the driver and the resonating pendulum??
The demonstration is most effective
in a darkened room with the cones
brightly illuminated by a projector.
Barton’s pendulums are a famous
demonstration of a resonance effect
Safety notes:Please ensure to turn the projector off when you have finished with the
apparatus.