CoolStuff Newsletters

Three Right Hand Rules of Electromagnetism

 

 
Teaching electricity and magnetism is complicated by the challenge that the magnetic forces are perpendicular to the motion of the particles and currents.  This requires a three-dimensional perspective which can introduce a variable of a “wrong” direction.  To prevent errors, let us be “right” and use the right-hand rule.
Some would claim that there is only one right-hand rule, but I have found the convention of three separate rules for the most common situations to be very convenient.  These are for (1) long straight wires, (2) free moving charges in magnetic fields, and (3) the solenoid rule – which are loops of current.  Calling these “rules” is the right name. They are not laws of nature, but conventions of humankind.  We use rules to help us solve problems, laws would be the underlying cause as to why the rules work.
Rule #1 – Oersted’s Law

Danish Physicist and Chemist

Our story begins with Oersted’s Demonstration, which was performed for the first time during a lecture in 1821.  What Oersted showed for the first time that when a current carrying wire passes over a compass the needle – which is a magnet – the needle deflects.  When it is underneath the magnet it deflects the other way. The direction that the magnet points is called the magnetic field around the wire.  And you can predict that with your right hand.

Replicating Oersted’s demo is quite easy to do. The compass is dialed to the north, the current flows from North to South and the compass underneath is deflected toward the West. In this case, I am using about 5 amps.

Point your right hand’s thumb along the flow of current – defined as the imagined flow of positive charge.  Now curl your fingers as if they were wrapping around the wire.  The direction that your fingers point, is the field.  I sometimes like to call this the RIGHT-HAND CURL, or Ampere’s Law.  Ampere himself described it as the face of a clock:  if the current flows into the face of the clock then the magnetic field would wrap clockwise.

As the current flows upward, the magnetic field will wrap around. Again, your thumb is the flow of current, and your wrapping fingers are the curl of the field.

Here is the situation in real life with the wire pointing upward and the compasses wrapped around. Normally they just point North, but when I turn the current on we see them all pointing around it, just as we predict with our right hand.

 A good way to demonstrate this phenomenon is with a set of the Small Clear Compasses.  When these are wrapped around a vertical wire, with no current, they will all initially point North.  But, if the current is switched on, the compasses will align in a loop around the current.  It is important to note that the compasses do affect each other, so finding the right distance between them can help make the demonstration more dramatic.
Rule #2 – The Lorentz Force

This second right-hand rule is usually applied to freely moving charges, called cathode rays, or otherwise to push on electric currents.

This cathode ray tube computer screen was originally all red. But these magnets have deflected the electrons from landing on their proper pixels. Note that the silver-colored cow magnet is more powerful than the plastic-coated ceramic iron magnet.

A goldfish is made green by application of a magnet. This is because the electrons (cathode rays) are hitting different pixels (phosphors) on the screen when they are deflected by the magnet.

A cathode ray tube computer screen is one vivid way to demonstrate the Lorentz Force. The screen is illuminated by moving electrons and moving charges are pushed about by magnetic fields.  This is a surprise to many people who think that magnets only affect metals such as iron and nickel.  (After using the CRT just leave it unplugged for a few minutes and that will restore almost all of the original screen color.)

The Electric Swing Apparatus proves that magnets affect currents and can demonstrate that the direction of that force obeys a right-hand rule.

Since electric current is made of moving charges we can also push it around with magnets.  One way to show this is with an Electric Swing Apparatus.  This will highlight that the current, field, and force are all three at right angles.

The magnetic field acts on the current in 3D. The direction of the force can be predicted with your right hand. Let your thumb be the current, I. Next aim your pointer finger in the direction of the magnetic field, B. Then the force will be directed along your middle finger, perpendicular to both of these.

The fingers are directed correctly along the vectors using the right hand.

Using your right hand, the current flows from positive to negative – thumb.  The magnetic field – pointer finger – is directed from North to South (that usually means from red to blue).  The force on the current is perpendicular to both of these and is predicted by your middle finger.

This 2nd rule is usually called the Lorentz Force named after H. A. Lorentz, a contemporary of Einstein, although its effects were known at the time of Michael Faraday.

Now, some people and some books prefer to use the palm to represent the force, that would be current field force (open hand).

The right-hand palm is a common alternative form of the same right-hand rule.

Another way to demonstrate this is with the Electricity and Magnetism Light bulb demo.  When there is alternating current, the wire vibrates, but when it is direct current we can apply force in a specific direction.  Using your right hand, it is possible to predict the direction the current is flowing.

This Edison-style light bulb has currents that are readily deflected by magnets.

For the flow of currents, which are the imagined flow of positive charge, it is appropriate to use your right hand.  But when it comes to negative currents, such as electrons, it is appropriate to use your left hand, which generates the opposite result that a positive charge would experience.  If one wishes to demonstrate the Lorentz force on a CRT, it helps to know to emphasize “use the left-hand rule for negative charges.”
Rule #3 – The Solenoid Rule

An air core solenoid can act just like a bar magnet. Repelling north and attracting south. In fact – if you trace the magnetic field with a compass, you can see that it truly matches the behavior a bar magnet perfectly

Using a third right-hand rule, we can we predict which side of the coil is north.

Let your curling fingers be the direction the current is flowing.  It is looping around.  Then your thumb will be NORTH end of the electromagnet.

This solenoid will behave exactly like this a bar magnet with a clearly defined North and South end. A compass emphasizes that – as far as the magnetic field is concerned – this is a magnet no different than the others.

The North end of the solenoid repels the North end of this bar magnet, in exactly the same manner as would another bar magnet. If the fingers of the right-hand point in the direction of current flow then the thumb will be the North side of the electromagnet.

Electricity and Magnetism are connected phenomena, but at right angles to each other.  So we use the convention of the right hand to predict the direction of the fields relative to each other.

Left Hand Rule

The right-hand rules assume “Conventional Current”, that is… current flows from positive to negative. College-based courses all go with that concept. NOT ALL high school physics courses use that concept. For example, some high schools use the “left-hand” rules because it deals with ELECTRON FLOW, that is… current flow from Negative to Positive (the direction that electrons flow from a battery for example).

The hand rules work the same but they are based on two different current concepts. In this blog we focused strickly on the right hand rule.


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The physics of a roller coaster loop

 
Each year millions of people will visit amusement parks in order to ride some of the fastest, highest, most extreme roller coasters. These machines thrill us because of their ability to accelerate us from a standstill to unbelievable speeds in a matter of seconds while changing from one direction to the next in an instant.
There is so much physics going on in the loop of a roller coaster. Angular velocity, centripetal acceleration, conservation of energy, and more! In this Cool Demo, we are going to look at how we can collect the data by using a Hot Wheels track and by placing a PocketLab Voyager on the Hot Wheels car.
By placing magnets at each connecting section of the track you can now generate “gate” times with PocketLab’s magnetometer. Using a 3D printer you can print a new set of connectors that are designed to house a small magnet. ( 3D print files are available to download in the resource section) When the car passes over these sections of the track you will be able to see a change in the magnetic field. Using this change and time we can come up with “timing gates” at each of these sections, and knowing the distance the car has traveled we can calculate the speed of the car.
The most obvious section of a roller coaster, or in this case, the Hot Wheels track is the loop. Although the loop of the Hot Wheel track is a circle, in reality, roller coaster loops have a tear-dropped shape that is geometrically referred to as a clothoid.
As the car passes through the loop, you can see the track bends into a tear-dropped shape. Once the car passes through the loop we are able to measure the angular velocity or the rate of change of the angular rotations, as it’s moving through that loop using the PocketLab’s Gyroscope.
Roller coaster rides are notorious for creating g-forces. The PocketLab also has an accelerometer, so as the car passes through the loop you can also measure the g-forces a person would be experiencing if they were traveling in the car. Traveling around a circle creates a centripetal force that the rider experiences as a g-force. The force is a function of speed and radius.

The Flip Flap Railway was built in 1895 and was the first roller coaster to have a loop. It was “famous” for its extreme g-forces that it produced on its riders of approximately 12 gs. The circular nature of the coaster’s loop along with its small diameter of 25 feet caused riders to experience neck injuries from whiplash. There are some interesting accounts where riders are hanging on for dear life in a death grip on the sides of the railcar and surviving a 12g ride which is absolutely nuts! Modern looping roller coasters all use teardrop-shaped loops to reduce the g-forces. The Flip Flap Railway was the last coaster to use a truly circular loop.

 
Looking at the Data:
  1. The time it took the car to travel through the loop = 0.34 seconds.
  2. The average angular velocity (gyroscope) through the loop = 1,170 degrees/seconds
  3. The average acceleration through the loop = 3.7 g
Data analysis:

Looking at the angular velocity inside the loop can be done in two ways:

  1. We can calculate the average loop velocity using our timing gates. (The time we exit the loop – the time we enter the loop and using the circumference of our track. Plugging in the geometry in our time we get 1.9 meters per second as our average velocity.
  2. Using the (1.9 m/s) velocity we can calculate the average angular velocity of 18.5 radians per second or 1060 degrees per second.

To get the g-force we need to calculate the following:

  1. Taking the timing gate data to calculate the G-Forces that would be felt inside the loop; (18.5 radians per second)²(0.1 meters per second) = 3.9 g.

The PocketLab Voyager has an array of sensors built into a small package. This allows you to measure data in scenarios such as this Hot Wheels Loop track experiment. Simply connect it to your smartphone or tablet through Bluetooth and you will be able to see the data live in the palm of your hands. On-board memory is also included for when you the PocketLab Voyager is out of Bluetooth range. The best thing about PocketLab Voyager is that that it comes packaged with some many features compared to equipment that costs thousands more.

Download lab resources:
  1. Click here to download – 3D print file (track connector Magnet Single)
  2. Click here to download – 3D print file (double track connector loop)
  3. Click here to download – Hot Wheels Loop Experiment Instruction

Explore the world around you with the sensors built into the PocketLab Voyager:

  • Measure Acceleration
  • Angular Velocity
  • Magnetic Field
  • Range Finder
  • Altitude
  • Barometric Pressure
  • Ambient Temperature
  • Humidity
  • Light
  • Dew Point
  • Heat Index

More Labs using PocketLab Voyager:

If you enjoyed this lab using a Hot Wheels track, we have two more you can download using a Constant Velocity Car and Air Powered Projectile.

  1. Click here to download – PocketLab Voyager with Constant Velocity Lab
  2. Click here to download – PocketLab Voyager with Air Powered projectile

 


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Demonstration of The Photoelectric Effect!

 

In 1905 Albert Einstein had his miracle year, publishing 5 papers, including the Special Theory of Relativity, the Mathematical Description of Brownian Motion, and the E=mc2 formula.  One of these papers was titled “On a Heuristic Point of View about the Creation and Conversion of Light.” [Ref 1]  In section 8 of this paper he develops a mathematic model that describes how light creates cathode rays.  What was heuristic was that he described light as “energy quanta” (photons) for the first time but what was worth a Nobel Prize, was that he was correct.

Figure 1.A –Max Planck presents Einstein with the 1929 Planck Medal for extraordinary achievements in theoretical physics.

Figure 1. B – Albert Einstein c1905 at the patent office desk where he worked as a third-class clerk, and occasionally worked on his “miracle” papers.

It is quite easy to demonstrate the photoelectric effect with an electroscope and a short wave UV-C lamp. By placing a negative charge on the electroscope, and shining the short wave UV light on top, it will discharge. Short wave UV is usually blocked by glass, but visible light is not, thus a pane of glass can be used to show that it is not just regular light that is causing the discharge.

Figure 2 – The electroscope is discharged by shining short wave ultraviolet light upon it.

It helps that on the top of the electroscope there is a zinc plate which has been scrubbed with steel wool.  This removes the zinc oxide layer and makes it more sensitive to the light.  Also note that if the experiment is tried with a positive charge, for example with a piece of glass rubbed with silk, it will fail to discharge.  This is because the photoelectric effect is only for electrons and will only work on negative charges because they are at the surface, but the positive charges are held deep in the nucleus by the strong force. In fact, the photoelectric effect is a great way to identify positive vs. negative charge.

With any form of visible light, you will not get the electroscope to discharge. It does not matter how bright the light is, even lasers will fail.  It takes ultraviolet, specifically the short wave UV-C, because even blacklights are not energetic enough to liberate the electrons.

The thing with light is, the shorter wavelength the more energy it has, and this was already well-known, from Max Planck’s formula  E = h f  but what was worth a Nobel prize, was the idea that the light hits one electron at a time.  Not as waves, but as individual pieces of light.  ONE particle of light hitting ONE electron at a time.  Einstein called this particle a quantum of light, meaning that it is a discrete exchange of energy.  We now call this a PHOTON.

Figure 3 – Albert Einstein took Max Planck’s formula for the quantization of energy in black bodies and extended it to describe light.  This implied that light delivered its energy in bundles of E=hf.  This was a new and heuristic idea, but it explained the photoelectric effect.  KE is the energy of the escaping electrons and W is the energy required to liberate them from the metal.

Figure 4 – The Phet Simulation of the photoelectric effect is a great way to engage students with the details of this modern physics concept. It is based on the experiments of Robert A. Millikan who proved Einstein’s perspective by experiment.

It is also possible to demonstrate the photoelectric effect with a small neon bulb.  These will turn on at about 70 volts.  Hook one to a high voltage source and then dial it back until it is just about to turn on.  Now it will be so sensitive, that just a little extra energy will make the electrons jump and conduct. This will NOT work for red and green light.  It must be blue, or ultraviolet.  That’s right, blue light ACTUALLY DOES have more energy than red and green light.  This is because light travels as photons, and the shorter the wavelength of light, the more energy per photon.

Figure 5 – The energy of blue light can cause electron conduction in a small neon bulb. The bulb stays on because plasma conducts better than rarefied neon.

Reference

http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_1905_heuristic.pdf


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Reflection, Refraction, Diffraction & Interference…… That’s COOL!

The Mini Ripple Tank is a great way to address the wave-energy standards and to teach about the properties of waves by showing how water waves behave.  This is in keeping with the history of physics and the modern experimental approaches to science instruction.

The Mini Ripple Tank eliminates the clumsiness of the larger ripple tanks of old and gives the opportunity for students and teachers to interact with the wave properties quickly and engagingly.  Because of the competitive price, and variety of available experiments.  It is even reasonable to buy a class set.

Fig 1.  Plane waves are being produced and are readily visible on the built-in screen.

Getting Familiar

The Mini Ripple Tank contains a small pan for water and a vibrating source.  The strobe light below projects waves of various frequencies on a fold-down screen.  Both the strobe and the wave frequencies can be varied, generating many interesting effects.  There is also a synchronizing mode which links the two (this is very helpful when measuring wavelength).

Fig 2. Water is filled up to half of the height.  The adjustable strobe projects from underneath.

The device comes with three distinct wave generating mechanisms: single source, double source, and plane waves.  The single source is the most fundamental and is helpful in instructing on wave basics and Huy gen’s Principle (plane waves are a sum of circular waves).  The double source can be used best at teaching interference experiments (more below) as well as testing out the diffraction formula.  The plane wave source is the one I tend to use the most often because it sets up a standard wave that can readily land upon the other implements which are used to redirect the waves.

Fig 3. The nine components.  Left to right: the two lenses and the prism, the two barriers and the parabolic mirror, and the double and single sources, as well as the plane wave source.

As for general tips, it is helpful to use a document camera for larger classes, also adding blue dye can sometimes improve visibility, and try to not overload the tank with water – either fill halfway or just enough to barely cover the lenses and prism.  Experiment a lot with wave and strobe speeds to improve the visibility of the desired effects.  

Refraction by the Lenses and the Prism

The bending of light waves by glass is well-known, but is this a property of all waves?  Yes! Demonstrate this dramatically by bending water waves with lenses and prisms.  The shallower the water, the slower the waves.  This is analogous to the denser the medium, the slower the light waves (with few exceptions).  

Fig 4. The prism can bend the waves by slowing their propagation.  

Again, remember to keep the water shallow.  Some experiments can include measuring the focal lengths of the two lenses (positive for convex, negative for concave), measuring the index of refraction for the prism (by wavelength change, speed change, or Snell’s Law), and measuring how water depth affects refractive index.  

Fig 5. The refraction formulas that can be used for quantitative experiments.  The first formula might be the least familiar – wavelength changes with index of refraction.  The second formula compares a standard speed c with the new slower one v to define the index n.  The third is the famous Snell’s Law.  

Somehow it is very satisfying to see the focusing of water waves when using lenses.  The ray approach to drawing images known as geometric optics does not provide a hypothesis as to the wave nature of light, but this experiment convincingly demonstrates that refraction and focusing is something that waves do!  Refraction and lens effects are a powerful piece of evidence that demonstrates the wave nature of light.  

Fig 6. The convex and concave lenses demonstrate convergence and divergence of waves respectively.

Reflection by Barriers and the Parabolic Mirror

The law of reflection can be readily demonstrated by the Mini Ripple Tanks (by stacking the barrier pieces) however, the best demonstration is the focusing of waves by the parabolic mirror.

When a plane wave enters parallel to the axis of a parabolic mirror, it will be reflected to the focus of that mirror.  This is the basis for Newtonian Reflector telescopes that remain the standard style in modern times.  A reversal can also be achieved by placing the single source at the focal point and reflecting out plane waves.  

Fig 7.  Reflection of plane waves off a parabolic mirror will focus them to a point.  

Diffraction by Barriers

le-slit diffraction of waves is easily demonstrated with this simple device.  Just place the barriers in the path of the plane wave source and the effect is immediately present.  Manipulating the opening and wavelength can help illustrate the variables: more diffraction occurs the smaller the opening is allowed to be.

Fig 8.  Single slit diffraction shows the bending of a plane wave source as it passes through an opening, illustrating Huygen’s Principle that plane waves are a sum of circular waves.

The diffraction formula for quantitative experiments is best applied to the two-source case, however, and while this is only a case of interference and not diffraction, it does provide an opportunity to apply the formula experimentally.    Here, we see both versions of the formula, the angular version, and the small angle approximation.  I prefer the second one because lengths are usually easier to measure than angles.    

Fig 9. The diffraction formulas:  The symbol d represents the distance between the sources, and lambda as always is wavelength (which is the dependent variable in this experiment).  Theta is the angular distance to an interference fringe as measured from the spot half-way between the sources.  X is the linear distance between the interference fringes, these are the locations of constructive interference.  L is the linear distance from the point between the sources to the point of interest, and because there is more than one location of constructive interference, m is the index number which labels these points as m=1,0,-1,2, etc, (any integer).  

Fig 10. An interference pattern is easily generated with these two sources.  The diffraction formulas above will apply to this double source interference pattern, even though no diffraction is occurring.  This demonstration can be converted into a quantitative experiment.

 


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Powering Imagination and Creativity OneCar at a Time

 

The OneCar is Arbor Scientific’s answer to the various needs of STEM Educators. It is an open-ended creativity-driven approach to science teaching that addresses cross-cutting concepts and offers an opportunity for tinkering and design.

Pictured here is one of the eight OneCar Packets which comes in every kit. Each can be used to construct eight different cars. Students can be creative.

The kit itself is jam-packed with 8 sets of experiment options, enough for large classes and extras for spare parts. A typical starter lab would be building the battery-powered motor car.

A motor in its housing slides into the chassis. These cars can be assembled and disassembled each class period.

This might be used for speed and acceleration experiments. But the options expand rapidly as more options are introduced.

The OneCar offers 8 ready to go experiment options. These can be extended and combined in creative ways to allow for the open-ended labs that STEM teachers have been searching for.

For example, the motor can be used to drive a fan or be powered by a rechargeable capacitor. The lessons can go beyond physics or include chemistry lessons such as air pressure and electrochemistry or even acid-base reactions. Perfect for Physical Sciences courses. There is more too. The Potential energy in a rubber band lab or the classic mousetrap car can be readily created using this kit.

The rubber band-powered car can be used to investigate potential energy.

The mousetrap car is a classic lab in physics used to teach energy and simple machines. Adding a lever arm and CDs for wheels is a common innovation.

You can also build a solar-powered car. Challenge your students to discover what can be done to optimize its traveling speed? Face it south? Angle the collar panel? Use a mirror to reflect the sunlight?

A solar powered car can be created and manipulated to optimize its efficiency. The solar panel can be either connected directly to the motor or, in this case, used to charge up one of the supercapacitors. Note how the solar panel is angled to be perpendicular to the sun, just like solar panels on rooftops.

All of these options can be mixed and matched. That is the whole idea of open-ended inquiry education. The OneCar gives students many opportunities to be creative in solving engineering challenges. Many of the above images come from videos on our website: ArborSci.com/OneCar.   Take a look and see how fun and easy it is to build these designs.

 


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Lab4Physics Classroom Edition Powered by Arbor Scientific

The Lab4Physics App is a helpful tool for teaching physics and physical science. It is a lab app for smartphones and tablets, and because of the familiar controls and friendly, easy-to-use interface, all your students can use it

 

The App works by using the built-in features of cell phones and tablets that convert easily to probeware, such as the accelerometer, which we will explore first.


Fig 1.  The Lab4Physics home screen.  When you open the app, there are lots of experiments you can try (which are categorized on the left) or you can go straight to the tools (right) and perform your own experiments.

 

ACCELEROMETER

 

If you shake the phone up and down, the accelerometer records this motion in 3D. Deleting the X and Z axis, we will now graph only the Y-vertical motion.

Fig 2.  It is easy to use the accelerometer to measure the earth’s gravity field strength.  Here the phone was held vertical then slowly turned to lay flat.  The gravity constant 9.8 m/s2 is measured.

The app allows you to zoom in, both vertically and horizontally, and slide the image around, just like a picture or map.  Because this interface is so familiar, students will already know how to do this.

Fig 3.  The phone’s Acceleration is measured in 3 dimensions, but typically you only need one.

Because the accelerometer is so easy to use, you will find yourself using it in many different applications, such as spring and pendulum experiments.  Note that when facing the phone, X is right and left, Y is up and down, and Z is toward and away.  The positive axes are right, up, and toward, which you can remember with thumb X, open fingers Y, palm-slap Z.

Fig 4.  Zoomed-in on the image of the above data.  Vertical zoom for precise amplitude measurements and horizontal zoom for precise time (period) measurements.

Fig 5.  A plastic bag is a convenient container for the phone when performing spring and pendulum experiments.  The touchscreen still works fine through the plastic.

 

SONOMETER

 

Using the microphone, Lab4Physics can analyze the intensity and frequency of a sound that the phone records. With this device, you can see the waveform of the frequencies that the phone picked up. Use this to compare the amplitudes of loud and quiet sounds or the frequencies of a high and low pitch.  This works as an instant oscilloscope. It is also possible to measure the period as the time between peaks, it helps to zoom in for this.

Fig 6.  The Sonometer makes a measurement of the author’s whistling ability.  The period can be measured as the peak to peak time, or the Highest peak frequency can be displayed automatically by using the Intensity vs. Frequency feature.

The waveform displayed looks transverse, but the sound is a longitudinal wave.  Therefore, it is important to explain how this wave was generated.  It was the motion of the vibrating microphone that moved a small magnet that generated the electricity that became the signal displayed. The device also can calculate the frequency of the loudest part of the signal it is detecting.  This can be used to test who sings with the highest or lowest frequency or just to check the frequencies of musical instruments.

Fig 7.  A tuning fork, which is supposed to be the musical tuning standard A 440Hz, is revealed to be very nearly correct by the Lab4Physics App’s Sonometer feature.

 

CAMERA / MOTION TRACKING

 

One of the most useful features is the ability to track an object’s motion.  Utilizing the phone’s camera, film an object (usually with a ruler in the picture), and by tracking at a specific point on the object, you can follow its motion through the frames of footage.

Fig 8.  An accelerating toy car has its motion tracked through ten frames of footage generating the expected parabola of an accelerating object.

 Because the frames are equally separated by time intervals the app can turn this data into a distance vs. time graph.  From this data, it further generates the acceleration and velocity graphs.  Even a Data Table is provided so you can sort out anomalous data or analyze further.

 

SPEEDOMETER

 

Lab4Physics also has a speedometer which is a streamlined alternative to stopwatches.  Students can, for example, set up a series of positions and click the split button to get the individual times for when the object is at that position.  Using this, graphs are generated for position and velocity.

Fig 9. A typical Speedometer experiment. Tracking the position of a toy car through space. Changing it from going slow to fast can show up on a position vs. time graph.

 

EXPERIMENTS AND LABS

 

Lab4Physics has lots of ready to go labs to instruct your students, or you can use them to give you ideas.  Here we explore some of the labs on waves.

Fig 10.  Left, a screenshot from the app shows the four labs on waves.  Choosing Do-Re-Mi takes us eventually to this screen, right, which shows how we will be exploring the frequency of a musical instrument.

 The labs take the students through the experiment in five or six steps.  They are self-contained and complete and let you know how much time the activity should take.

 


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test

Cool Stuff Demos with Violet Lasers

 

If you are talking about optics in the classroom and students are learning about how light waves behave, take a look at the blue-violet laser, which produces wavelengths at 405 nm.

“I definitely want one of those blue LASERS! Ahhhh… to write my name on a phosphorescent board the FIRST day of class in the dark from the back of the room. That WILL get their attention!”   -Buzz Putnam

 

Sure, it is a different color and that is always cool, but why use this over any other Laser?

  • Cover most of the visible spectrum – If you only have the red (650nm) and green (532nm) Lasers, you are still missing a large part of the visible spectrum. At 405nm, the blue-violet Laser provides a good representation of the shorter wavelengths present on the opposite end of the visible spectrum from red.
  • Diffraction grating differences – You can compare the red, green, and blue-violet Laser colors by pointing them through a diffraction grating to observe where the different wavelengths end up.
  • More Fluorescence – Unlike the green Laser, the blue-violet Laser can produce fluorescence on a wide variety of materials. In other words, the blue-violet wavelength of 405 nm excites the electrons of most materials to a higher energy level than the green Laser.
  • More phosphorescence – For your next trick, we recommend shining the Laser on something with “glow-in-the-dark” properties, such as a sheet of glow-in-the-dark paper. The effect, called phosphorescence, is due to the same characteristics of excited electrons that we saw in florescence. Only with phosphorescence, it takes longer for the material to transition back to its ground state, and therefore you see it longer with those types of materials. The green Laser does not produce these same effects. Show your students both situations and ask them why!

 

Why pay $79 for a violet LASER

Arbor Scientific has carefully screened all of our Lasers to make sure they offer a higher level of safety and peace of mind. There are low-cost versions available on the market today that could pose serious risk to your students due to a lack of infrared (IR) filters. Even pointers that use IR filtering could still be harmful, due to shoddy manufacturing that provides poor conversion efficiency (when converting from infra red to visible light). While all Lasers should be handled carefully to prevent users from harm and should never be pointed at unprotected eyeballs, these lower cost Lasers are particularly problematic in the academic atmosphere where there are many people in close proximity. For the safety of your students, please always make sure you have taken all the proper precautions possible, including the use of effective IR filtering.

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Phosphor Glow Paper

Specially coated paper absorbs light and emits it slowly. Use a camera flash to create lasting shadows and explore phosphurescence. Try different colors and intensities of light – even ultraviolet!

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Deluxe Green Laser Pointer

With a range of 2 miles the Deluxe Green Laser Pointer has the highest output power allowed by the FDA! 532 nm green laser pointer includes two AAA batteries.

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Standard Red Laser Pointer

The powerful laser emits a beam at a frequency of 650nM that can focus upon a board or diagram — anywhere you want your audience’s attention — up to 500 yds away.

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Laser Tripod

Clip-on stand makes hands-free laser use a snap! The tripod comes with a mount that will hold down the ‘on’ button of our laser pointers. The angle is fully adjustable. Use the Velcro® strap to attach it to a ring stand or solid object.

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Air Powered Projectile in-depth look [W/Video]

The Air Powered Projectile in-depth look

One of the best ways to engage your students in the study of projectile motion is with direct experiment and observation. For this purpose I recommend the air-powered projectile. It safely and reliably demonstrates projectile motion by simply releasing compressed air. Here are five experiments to get you started.

launch
The soft nose cone provides a high degree of safety while the body’s sleek design minimizes the effects of air resistance.
soft_nose

MEASURE LAUNCH VELOCITY
Shooting the projectile straight up is the easiest way to determine launch speed.
The first thing you want to do is determine the launch velocity by shooting straight up. It takes about 5 seconds to go up and come back down when shot vertically. Use the formula v=vo+at , analyze the top of the trajectory. At this point velocity = zero. Then set gravity to negative 10m/s/s. Gravity is pulling opposite the initial launch velocity, which is the unknown. Plugging in 2.5 seconds for time (assuming the trip takes the same time up as down) we get a launch velocity of about 25m/s. You might be concerned whether this is a safe speed, but the soft nose c one, and the fact that there is no chemical propellant ensures this. You may wish to wear safety goggles anyways.
launch-1

The calculation of launch velocity is straight forward, requiring only algebra.
algebra

ANGLE vs RANGE
A classic experiment that I have done every year since I started teaching is to investigate which angle generates the greatest launch distance. Students will have their own hypothesis. Without doing any math, try to hypothesize which angle will maximize the range. This is an experiment that works in both high school and middle school. The theoretical result is that 45 degrees maximizes range.

r-a

Sample data for the Range vs Angle Experiment. Note the systematic error on the zero.
This is because the product of horizontal velocity and time in the air is maximized. The mathematical proof is a common homework problem in Honors Trigonometry classes and can be done without calculus. When you plot the data, a surprising result is that the complementary angles, like 30 and 60 degrees can have the same range as each other. This is because when the velocity is more horizontal, the vertical time is lessened, and vice versa.

wedges

Angled Wooden Wedges help a lot in this experiment. The angle of launch will be the compliment to these angles.
When performing this experiment, it is helpful to use the angled wooden wedges option. These help adjust the angle without the use of clumsy blocks of wood or coupling. Another addition you might want to invest in are the varied speed end caps. The different size caps affect the pressure limit that causes the seal to slip, launching the tube upward with the force of expanding gas. Larger endcaps can capture more of that force so it will go faster. This adds another variable which allows you to make new predictions. But with the same endcap, you get the same time, every time.

caps

Different sized end caps can change the launch velocity, adding a new variable.
ADIABATIC EXPANSION
The air powered projectile does not use any chemicals to launch. It only uses the compressed air of a bike pump, typically around 60 psi (pounds/square inch). When you launch the projectile, you will usually see some clouds appearing beside the base. They only last for a second, but can be made more visible by using a high speed camera. (Many students now have these in their smartphones.)

Adiabatic

Adiabatic clouds appearing during a typical launch event. This image was taken with an iPhone 5s in 120 frames/second mode.
The clouds are caused by the humidity in the air being turned into a vapor due to the rapid temperature change. When a gas expands rapidly, it cools. This is called adiabatic expansion. It is an important idea in thermodynamics and this is a really good example of it. You’ve probably seen it when you open a champagne bottle, or even a soda.

Because the force of launch only acts in the initial moment, the rocket is an excellent example of a free falling projectile (unlike missiles and rockets). The sleek profile minimizes air resistance and turbulence while increasing the accuracy of the experiment.

HIGHLY ACCURATE CALCULATED LANDING SITES
In video we launch the air powered projectile at 30 degrees, and from the first experiment, we already know the initial velocity, Vo=25m/s. We use Vo sin30 to find the initial upward velocity (12.5m/s) and Vo cos30 to find the horizontal component (21.6 m/s).

board

A typical projectile motion problem can now be performed experimentally, with a high degree of accuracy and while being highly engaging.
At the highest moment, it is only moving horizontally, so we once again can use v=vo+at. Only this time the plug step is 0=12.5-10t giving a time of 1.25 seconds to reach the top. Twice that is 2.5 seconds, the total time of flight.
The product of the horizontal component and the total time of flight is the distance traveled. (The horizontal velocity never changes.) The range, x=vhoriz * time = 21.6m/s * 2.5 sec = 54 m.
That the theoretical prediction. Take it with you, and some measuring tape (or the yard lines on the football field) and see what really happens.

field

The impact location proves to be within 2 meters of the expected value.
When we did the experiment we got a result of 56 meters. That is less than 4% error, very good!


james_lincolnJames Lincoln

Tarbut V’ Torah High School

Irvine, CA, USA

James Lincoln teaches Physics in Southern California and has won several science video contests and worked on various projects in the past few years.  James has consulted on TV’s “The Big Bang Theory” and WebTV’s “This vs. That”  and  the UCLA Physics Video Project.

Contact: [email protected]

 


 

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You’re Getting Warmer! [W/Video]

The Little Shop of Physics has developed a series of videos called Flash Science, which show some exciting experiments that can be done with everyday items to demonstrate physics principles in a unique way. All of these experiments have been designed to be done by trained adults using proper safety equipment.

Heat

In physics, heat is something you do; it’s a verb. It is defined as the thermal (non-mechanical) transfer of energy. When you heat an object, you transfer energy to it, which can raise its temperature or even cause a phase change. Traditionally, three sources of heat transfer are cited: convection, conduction and radiation.

Radiation

Radiation is the transfer of thermal energy using electromangetic waves, which includes visible light, infrared radiation, ultraviolet radiation, x-rays and microwaves and radio waves. A camera flash is designed to give off a whole lot of visible light in a short amount of time. The black ink in the newspaper absorbs this radiation and increases in temperature, while the blank paper reflects the light and does not warm up nearly as much.

Conduction and Convection

When a flame is held underneath a balloon, it’s no surprise that the balloon pops. The flame is at a high enough temperature to heat and melt (or even burn) the balloon, and the air under pressure inside quickly escapes. However, when the balloon is filled with water, the flame no longer pops it. The balloon is very thin, and the thermal energy quickly gets conducted to the water on the inside. The water has a very high heat capacity, so it takes a large amount of energy to increase the temperature of the water.

The water is also effective transferring the thermal energy away from the flame. The water will undergo convection; the warm water by the flame will move upwards, and be replaced by colder water coming in from the sides. Also, since water evaporates at 100°C, liquid water has a limit on how high of a temperature it can reach.

Evaporation

Evaporation is an extremely important and sometimes overlooked form of thermal energy transfer. Evaporative cooling is the mechanism behind human sweating, and the energy stored in evaporated water is extremely important in the Earth’s weather system.

In this video the flame hounds are soaked in a mixture of rubbing alcohol and water. While the alcohol burns, and releases thermal energy, the water evaporates and takes much of that thermal energy away from the flame hounds, so that it does not burn!

If you’re careful, you can even hold flaming bubbles in your hands!

Plasmas

Running electricity through the graphite pencil-lead causes the tip to get extremely hot, so hot that the graphite vaporizes and the vapor ionizes. These hot ions are used to cut aluminum foil, similar to how a plasma cutter or arc cutter works.

Erasing With Heat

Some erasable pens use thermochromic ink, which changes colors from dark to light when it is heated. When the ink is cooled (such as through the evaporation of a liquid), the ink becomes dark again. With this ink, you can erase and re-write messages over and over again!

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Arbor Scientific’s Video Contest Winners Announced

For ten weeks starting in December 2016, physics educators and their students have been uploading their short videos that capture demonstrations of physics in the world- in Slow Motion. The contest was the first of its kind by Arbor Scientific, the educational leader in finding cool science tools for making understanding scientific principles easy, fun and exciting for today’s students.
Arbor Scientific asked Paul Hewitt, a renowned physics professor and author of the best selling textbook Conceptual Physics*, to review all the video entries and choose the winner. Hewitt said “It has been a pleasure watching these. I chose INERTIA BLOCKS, mainly because of the 4 sheets pulled at the same time; a nice lift to a familiar demo”. The second winner was based upon popular votes at the contest website, receiving over 380 fan votes!

 

Both winners will receive a $100 Arbor Scientific gift certificate which will help them purchase new classroom science products, a profile on Arbor Scientifics Blog “CoolStuff” and in the CoolStuff e-newsletter mailed to over 20,000 educators monthly.

 

Amador Valley High School Watch their entry video INERTIA BLOCKS

Amador Valley High School: Students stacked blocks with cardboard pieces attached to string in between. They were able to pull out the cardboard and see that the inertia of the blocks resisted changes in motion enough to stay where they were.


Manistee High School Watch their entry video CONSERVATION OF MOMENTUM


 

Conservation of Momentum by Manistee High School
Hypothesis: The higher density ball when colliding with a lower density ball will knock the lower density ball back no matter the size. Goal of

Experiment: This experiment was testing how collision is affected by the masses of the objects colliding at the same speed. This experiment also tests and confirms Newton’s Third Law of Motion: For every action, there is an equal and opposite reaction.

Materials:

  • Four Balls Were Used in This Video:
  • Two basketballs of an equal mass of 600.29g
  • One Volleyball with a mass of 274.19g
  • One Shot Put with a mass of 4200g

A ramp was placed on both sides of the track to launch the balls. The ramp was 7m tall, two people let the ball roll down the ramp at the same time, then observed the results.

There were three trials conducted in this experiment:

  1. First trial: Two basketballs were rolled down the ramp colliding and knocking each other back an equal distance
  2. Second trial: The basketball from the previous trial and a volleyball were rolled down the ramp. The volleyball was knocked back farther than the basketball
  3. Third Trial: The same basketball was used once again and a shot put were rolled down the ramp. The basketball was knocked back significantly by the shot put.

Conclusion: When objects collide the size of the object has little effect compared to the density (Mass) of the object.
“I’m excited for both of our winners,” said Andrea Kelly, Marketing Manager at Arbor Scientific. “They both encompass what we were looking for: presentation, substance and a passion for physics. We surpassed our goal of over 50 video entries and were impressed with the knowledge and creativity all had. We will definitely do similar contests in the near future.”

The submissions can be viewed in their entirety at www.slowmophysics.hscampaigns.com and will eventually be moved over to the website and blog to remain resources for teachers going forward.

Thanks to everyone for your participation!


*Conceptual Physics Alive! On Demand by Paul Hewitt is online on Vimeo here!

 

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