Download Useful Demonstrations for Units 1 to 4

2014 STAV/AIP Physics Teachers Conference
Day 1: Friday 14 February
Paul Fielding, Billanook College
Paul Fitz-Gerald, Ivanhoe Girls’ Grammar School
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Demonstrations for Physics Units 1 to 4
The following contains details and information to help you run useful demonstrations to help
student understanding of physics concepts. The demonstrations generally use commonly available
equipment and materials.
Magnetism
Showing magnetism is a vector using compass and 2 (or more) bar magnets. PF
S
S
N
N
S
N
N
S
Oersted’s experiment. Use long enough wire so power pack does not shut-off. Alternative is a 6V
lantern battery but it does drain quickly when shorted, plus it says on the side of the battery that it
may explode. PF
Activity booklet PFG
Electricity
Lenz’s law tube, and ‘post box’. The tube can be purchased from suppliers, the post box is
homemade. PF
Faraday’s experiment, looking for the changing magnetic field to produce a current. Demo. PF
Parallel and series circuits – watch for different bulbs – use resistors rather than bulbs. PF
Electronics and Photonics – use components: thermistor, LDR etc, use log graph paper
I print graph paper into prac sheets. Students need to understand log scale graphs, and plotting
their own is a good way to learn this. I use the program “Graph Paper Printer” by Philippe Marquis
and simply cut and paste in. Use log-linear for thermistors to plot resistance (log scale 4 decades
from 1, to 10000 Ω) versus temperature.
Coils experiment showing the relationship between turns and voltage (transformers). PF
AC/DC. Rectification circuit. With 4 LEDs set up a
full wave rectifier, and one set up as the load.
(Only one load resistor required). Connect to a
signal generator (sine wave 0.5 Hz) to show which
part of the rectifier is conducting. PF
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Investigating the resistance of a thermistor
Aim:
To investigate the effect that a change in temperature has on the resistance of a thermistor
Equipment:
• 1 x thermistor (Dick Smith Electronics Cat No. R1895 or similar)
• multimeter
• connecting wires
• hotplate
• 500 mL Beaker
• blu-tack
• Thermometer (-5oC to 110oC)
• 6V lantern battery
• Resistor to build voltage divider circuit 22kΩ
Method:
Wrap the thermistor wires with blu-tack in order to create a waterproof
barrier. The thermistor needs to contact the water.
The circuit is to be set up as a voltage divider. The thermistor and resistor are
to be connected in series and connected to the 6V battery.
The voltage across the resistor is to be measured with the multimeter.
Step 1 Measure the battery voltage and an accurate measurement for the
fixed resistor.
Step 2 Fill the beaker with about 200 mL of chilled water (with a small amount of ice slurry) and place the
thermometer into the water and measure its temperature.
Step 3 Place the thermistor into the beaker of water. Do not let it touch the glass walls of the beaker and
make sure that its leads do not touch the hotplate. Wait until the temperature is stable before you start taking
results.
Step 4 Read the voltage across the resistor using the multimeter.
Step 5 Calculate the resistance of the thermistor.
Step 6 Turn the hotplate to high and record the thermistor’s resistance at 10 oC intervals until the water just
starts to boil.
Results:
Once you have recorded your results, you then need to work on your own.
Your report should include:
Appropriate titles and headings
Your data neatly recorded in an appropriately labelled results table
A carefully drawn circuit diagram showing all components used
A complete sample calculation for the thermistor resistance at 30 oC (starting from the voltage divider
formula)
A plot of the Thermistor’s resistance (kΩ) against temperature (oC) on appropriate graph paper
A line of best fit shown
A conclusion drawn from your results about the behaviour of a thermistor as a temperature measuring device
The report should also contain respond to the following:
Question 1
State the definition for an ohmic device and then explain whether you think the thermistor
displays ohmic or non-ohmic characteristics.
Question 2
Use your graph to predict at what temperature the thermistor’s resistance will be 30 kΩ.
Question 3
Use your graph to predict the thermistor’s resistance when the temperature is 65 oC.
Question 4
Explain very briefly how thermistors are used in household appliances.
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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10000
1000
100
10
1
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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The Light Dependent Resistor (LDR) and Changing Light Intensity
Aim:
To investigate the resistance of an LDR as the intensity of
the incident light on it changes.
Equipment:
• 1 x Light Dependent Resistor (LDR)
(Dick Smith Electronics Cat No. Z4801)
• torch or Hodson light box
• 6 x primary red filters from the Hodson light box kits
• blu-tack
• empty 35 mm opaque film canister
• multimeter
• connecting wires
(banana plug & alligator clip at either end)
Your teacher will have already placed the LDR inside the film canister with a hole drilled in the bottom to let light in
for you.
Using A Multimeter
Caution:
Do not use the multimeter to measure the resistance of a load in a circuit whilst the circuit is ‘live’. You
risk damaging the multimeter if you do. Instead remove the load from the circuit and measure its
resistance using the Ohms (Ω) scale on your multimeter.
Method:
Set up your equipment as shown in the diagram above. Use blu-tack to hold the film canister and torch
in place.
Step 1
Connect the multimeter across the ends of the wires of the LDR.
Step 2
Place the torch (Hodson light box) about 20 – 25 cm from the LDR.
Step 3
Turn the torch (Hodson light box) on. Direct the light so that it shines through the hole in the bottom of
the film canister and onto the LDR. Place one of the primary red filters against the end of the torch. This
represents the initial intensity, Io, of your light source.
Step 4
Record the resistance of the LDR for this initial intensity, I o.
Step 5
Place each additional primary red filter in front of the torch and record the LDR’s resistance. This will
give you six data points that you can plot.
Results:
• Enter your data into an appropriately labelled results table.
• Plot a graph of the LDR’s resistance (kΩ) against Intensity, I, (number of filters from 0 to 5).
• Draw in a line of best fit for your data.
Discussion:
Question 1
Does the LDR behave as an ohmic conductor? Explain your answer.
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Part 2B – The Light Dependent Resistor (LDR) and Constant Light Intensity
Aim:
To investigate the resistance of an LDR as the intensity of
the incident light on it changes.
Equipment:
• 1 x Light Dependent Resistor (LDR)
(Dick Smith Electronics Cat No. Z4801)
• 1 x 10kΩ resistor • torch or Hodson light box
• 1 x primary red filters from the Hodson light box kits
• blu-tack
• empty 35 mm opaque film canister
• 2x multimeter, or 1 voltmeter and 1 ammeter
• connecting wires
Caution:
Do not use the multimeter to measure the resistance of a load in a circuit whilst the circuit is ‘live’. You
risk damaging the multimeter if you do. Instead remove the load from the circuit and measure its
resistance using the Ohms (Ω) scale on your multimeter.
Method:
In the space provided below draw a circuit that shows the LDR and the 10kΩ resistor connected in
series with a 12V variable power supply. Include in your diagram an ammeter and voltmeter so that they
can be used to measure the current flowing through, and potential difference across the LDR.
Remember to use a ruler when drawing your circuit diagram.
Step 1
Connect the multimeter across the ends of the wires of the LDR.
Step 2
Place the torch (Hodson light box) about 20 – 25 cm from the LDR.
Step 3
Turn the torch (Hodson light box) on. Direct the light so that it shines through the hole in the bottom of
the film canister and onto the LDR. Place one of the primary red filters against the end of the torch. This
represents the initial intensity, Io, of your light source.
Step 4
Record the resistance of the LDR for this initial intensity, I o.
Step 5
Using the appropriate pieces of equipment set up the circuit you designed so that you can measure the
current flowing through, and the potential difference across the LDR.
Step 4
Set the variable power supply to 2V and record the current flowing through, and the potential difference
across the LDR.
Repeat this process for settings on the power supply of 4, 6, 8, 10 and 12V.
Results:
• Enter your data into an appropriately labelled results table.
• Use the data you have collected, and the definition of resistance, to calculate the LDR’s resistance
for each of the settings on the variable power supply.
Discussion:
Question 1
Based on your results and calculations, does the resistance of the LDR change when the intensity of
light falling on it is constant but the potential difference across it and current flowing through it change?
Conclusion:
Use a summary of your results to the two parts of this experiment to summarise what you have learned
about LDR’s.
Dick Smith Electronics
Thermistor
http://www.dse.co.nz/dse.filereader?4d40d3f90073fcde2742c0a87f3b071c+EN/catalogs/SUP1000077
Light Dependent Resistor LDR
http://www.dse.co.nz/dse.shop/4d40d3f90073fcde2742c0a87f3b071c/Export/catalogs/SUP1000072
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Modelling electric current
using your students and
M&Ms.
This is my slightly modified version of one of Christina Hart's models for electric circuits that she
presented at the Physics Teacher's Conference a few years ago. Her original articles can be found on
the VICPhysics website via the url below.
Model 4: Energy in a simple circuit:
The ‘smarties’ model
By Christina Hart (STAV Physics Teacher's Conference 2008)
http://www.vicphysics.org/electricity.html
Instead of each student representing a single electron I have each student represent one coulomb of
charge, and that the atoms of their body represent the number of electrons that are required to make
up one coulomb of charge.
Remember to have your students move from the negative terminal of your battery to the positive
terminal.
The charge on a single electron is 1.60 x10-19 C.
It takes 6.25 x1018 electrons to make up one coulomb of charge.
→
−19
÷1.6×10
coulombs×1.6×10
−19 electrons
←
The M&Ms are still use to represent energy, the energy that each coulomb of charge has. It is also
important to impress upon the students that energy is not a thing – even though we are representing
it with sugar coated chocolate!
Using this modified model I can talk about:
Current.
Current (A) = charge (q) / time (s)
The number of students that walk past a point in the circuit each second is equal to the current flow
in the circuit.
Energy
Energy (J) = voltage (V) x charge (q)
The number of M&Ms given to each student represents the energy in joules given to each coulomb
of charge that flows out of the battery. This energy has to be 'given up' to the various loads within
the circuit so that each coulomb of charge returns to the battery with 0J of energy.
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Light
Figuring Physics – Hewitt Drewit!
The Physics Teacher – Vol. 37, Feb. 1999
Question
The lens projects an image of a white candle on a screen. How would the image differ if the top half
of the lens is covered with a green filter and the bottom half with a red filter?
green filter
object
image
red filter
convex lens
Answer
The image of the candle will be yellow. Each and every part of the image on the wall is formed
from light that passes through each and every part of the lens. The red and green light transmitted
by the lens will simply overlap and average to be yellow.
Additional Questions
Write down your predictions to each of the following questions,
trial them experimentally and comment on your findings.
1. How would the image differ if the top half of the lens is
covered with a red filter and the bottom half with a blue filter?
green
red
blue
2. How would the image differ if the lens was 1/3 covered with a
red filter, 1/3 covered with a blue filter and 1/3 covered with a
blue filter as shown in the diagram to the right?
3. How would the image differ if the bottom half of the lens was
covered by an opaque card?
Answers
1. The image of the candle will be magenta. Each and every part of the image on the wall is formed
from light that passes through each and every part of the lens. The red and blue light transmitted
by the lens will simply overlap and average to be magenta.
2. The image of the candle will be white. Each and every part of the image on the wall is formed
from light that passes through each and every part of the lens. The red, blue and green light
transmitted by the lens will simply overlap and average to be white.
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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3. The image of the candle will be white, but dimmer. Each and every part of the image on the wall
is formed from light that leaves each and every part of the candle and passes through the
uncovered half of the lens. See the accompanying ray diagram.
opaque filter
object
image
f
•
f
•
convex lens
Marbles in a flask (TIR) PF
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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The Invisible Beaker
Place a 150 mL Pyrex beaker, preferably
without any writing on it, inside and in the
middle of an empty 500 mL beaker.
Now pour some canola vegetable oil into the
smaller beaker until it overflows and
eventually is surrounded inside and out by the
canola oil.
What do you ‘see’ happening to the 150 mL beaker as the oil overflows into the larger beaker?
Use your understanding of refraction, reflection and how it is that we actually get to see things to
explain what you have just seen.
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Answer
In order for us to see an object, light from the object has to reach our eyes. There are two ways in
which this can happen. The first is that the observed object is luminous and the light we see comes
directly from it. The second occurs as a result of scattering (reflection) whereby light from a source
is reflected from off the object to our eyes.
When light is incident at a boundary between two materials of different refractive indices (optical
density) as well as refraction occurring, some of the light is reflected. Hopefully you and your
students will have noticed this when you did the refraction experiment on pages 80 and 81 of
Science Links 3. An example of this partial reflection from the boundary between two surfaces is
shown in the diagram below. Remember that the angle the reflected ray makes with the normal will
be equal to the angle of incidence.
So how does the demonstration work?
Well, in this particular instance the Pyrex glass and the Canola oil both have the same index of
refraction; therefore there is no light reflected (scattered) from the glass-oil boundary and the 150
mL beaker magically disappears!
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Reflection Illusions - The Cold Candle
PIRA 6A10.60
http://www.physics.isu.edu/physdemos/optics/reflect1.html
Place two identical candles on opposite sides, and equidistant from, a vertical pane of clear glass as
shown at right. Adjust their positions so that each lies at the image point of the other for reflections
from off of the glass. If only one candle is lit, it appears as if the other one is lit as well, if the
observer is on the same side of the glass as the lit candle. This works best on a wheeled cart that can
be turned to show the view from different angles and from the other side.
An amusing variation is to have one of the candles inside a beaker, but still at the image point of the
other candle. With the other candle lit, the beaker can be filled with water to make it look as if the
candle is burning underwater.
This is the basic idea behind a whole series of vaudeville stage illusions, such as the "head in the
box" and the "ghost king on the throne" tricks. The Haunted House at Disneyland uses this quite a
bit too. David Copperfield used this to make the Statue of Liberty "disappear".
And the magic candle that burns under water…
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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YouTube Video Clip
http://www.youtube.com/watch?v=YqbRiz9Ky50
Explanation:
http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/peppers-ghost/
Although glass is mostly transparent, it
reflects a significant proportion of the light
that hits it. Normally the light going
straight through is so much brighter that
you can't see it, but if you use something
bright, like a candle, in front of the glass
and a dim room behind, the reflection can
dominate what you are seeing.
So you see the reflection really well. The
neat thing about reflections is that they
look as if the object is behind the mirror.
So when you move your head, the
reflection moves in exactly the same way
as the candle behind, so the illusion works
from lots of directions.
The demonstration clearly shows that an image formed in a plane mirror is:
• Virtual
• Upright
• Same size as the object
and
• Laterally inverted (look carefully at the candle flame and its image when it flickers)
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Colour Addition
A useful set up uses 3 overhead
projectors. I cut out some circles in
manilla folders and stuck on
coloured cellophane. Two layers for
blue and red, 3 for yellow.
This gives surprisingly good results,
the centre is close to white.
I usually show an app that labels
the colours. PF
Subtraction of colour
Use quality filters PFG
With secondary filter (eg magenta that
lets through red and blue) on overhead,
overlap with another secondary (eg
yellow, that lets through red and green,
therefore the overlapped section will be
red)
magenta
blue
(s)
(p)
red
cyan
(p)
(s)
green
(p)
yellow
(s)
white
Light Spectrum
Turn on camera on computer (webcam, iPad etc) on point a remote
control at it. Pressing buttons will flash codes on the IR LED. This
part of the spectrum is “seen” by a CCD camera.
Human view versus insect/predator view. pfg
Polarising – insects (eyes – IR and UV) CCD camera spectrum
Polarising lens demo. Sticky tape of microscope slide. PFG
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Sound
Speed of sound with starting pistol,
Vibrations (toys, wine glass),
Sound in vacuum (Bell jar and vacuum pump),
Video – hearing test can be easier than running frequency generating software
Spectrum software (iPad SpectroPro, SpectrumView)
Investigation Experiment (collect points)
Resonance equipment (3 points)
- use resonance equipment to find the fundamental frequency
- find nodes and antinodes and determine distance between them
- compare the above 2 results
Speed of sound in air versus steel (2 points)
- use a section of the pipe railing of the fence around the top oval
- one student lightly tap the pipe with a hammer
- another student a distance away places their ear on the pipe
- compare the sound of the tap as it arrives through the steel, compared to through
the air
- Safety: take care with hammer and only tap lightly
Strobe on electric fan/guitar string/vibrating object (1 point)
- use stroboscope to measure frequency of rotating and vibrating objects
- Safety: do not stare into strobe light
Chladni plate (1 point)
- watch a Chladni plate video from youtube
- vibrate plate with violin bow
- produce and describe different patterns obtained
- analysis of frequency versus pattern bonus +1 point
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Motion: Forces
Fluffy dice/Student demonstration PF
3rd laws PFG
Sparkvue
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Nuclear
M&M’s decay PFG
Decay rate and half-life of Dice – ‘order out of randomness?’ (assembled by Martyn Wood)
Introduction: Radiation occurs when a radioactive nuclei decays, emitting a particle or energy.
If we have a block of radioactive nuclei is there a pattern to how they decay?
If there is a pattern, how do the nuclei know when it is their turn to decay?
Experiment:
Collect 100 small die, each dice has one red side.
Put the die in the container, give it a quick shake and turn the container upside down.
Place the red die on one side in a column.
(When you remove them place them in lines and build a bar chart)
Repeat the experiment three times.
Record your results in the table and collect the results for the class.
Roll
Count
Expt. 1
Count
Expt. 2
Count
Expt. 3
Total count
Expts. 1-3
Total count
for class
0
1
2
…
30
Analysis:
To analyse the results we will draw two graphs using EXCEL
Graph 1 – results of expts 1-3, plot Count v Roll number
Graph 2 – results for the whole class.
Print the graphs and staple into your booklet
Is there any pattern in the graph?
Do you recognize this shape of graph? What it is called?
Does the pattern become clearer?
What is the probability of getting a red side when you role a dice?
Using Graph three calculate the half-life in minutes. We will assume it takes 1 minute between
rolls
The following equation describes how radioactive isotopes decay
N = No e-λt
N = final count
No = Start count
λ = Decay rate of die
t = time
e = mystical number in nature = 2.71828
Using your calculator sub you values of N, No, t and e and find the value for λ.
Extension question:
If there were three sides painted black what would you expect the number of roles to be for half
the die to ‘decay’?
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Detecting radiation with a Geiger-Müller tube demonstration (based on Heinemann exp)
TASK
To investigate the penetrating ability of three common types of nuclear radiation and the ability
of different materials to absorb the energy associated with nuclear radiation.
THEORY
Besides the obvious fact that none of our senses can
detect individual decay events, the nuclear decay
process seems to be random, yet, at the same time,
predictable. It is impossible to say which nucleus will
become unstable enough to decay next, but it is fairly
easy to use a Geiger counter to count the number of
nuclei which decay per second throughout a radioactive
sample.
DATA & ANALYSIS
Part I: Background radiation
Count 1:
Count 2:
Count 3:
Count 4:
Average count during activity:
……….
……….
……….
……….
……….
1. How do these values demonstrate the random nature of radiation.
Part II: Radiation shielding - Source Am241
Record your final data as the net count per 60 seconds (i.e. the recorded count minus the
average background count).
Alpha Source
Material
Beta Source
Count
Material
Gamma Source
Count
Material
Air
Air
Air
Paper
Paper
Paper
Glass
Glass
Glass
Aluminium
Aluminium
Aluminium
Lead
Lead
Lead
Count
QUESTIONS
1. Which type of radiation is the most penetrating?
2. Which type of radiation is the least penetrating?
3. What generalisation can you make about the effect of the thickness of the shielding material
on the count rate?
4. What generalisation can you make about the effect of the density of the shielding material on
the count rate?
5. Why was background radiation measured? Do you expect the value to be constant?
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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Light and Matter
Microwave kit (IEC)
Lots of useful phenomena can be demonstrated. Reflection, diffraction, polarisation, interference
patterns, and MODULATION. pf
Guess the gas activity (very high voltage)
I set up different discharge tubes. From their desks,
students can look through spectrascopes, measure
dominant emission lines, and using charts, work out what
gas it is. Don’t forget the fluro lights give mercury lines.
Ideas for Year 11 and 12 Physics Extended Experimental Investigations
From Dr Richard Walding, FAIP, FRACI, CChem, Griffith University, Australia
Author New Century Senior Physics textbook by Oxford University Press.
Email: [email protected]
http://seniorphysics.com/physics/eei.html
P Fielding, P Fitz-Gerald STAV AIP Physics Teachers Conference 2014
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