Operating nstructions: WLS1804-45 CENCO Ring Launcher PRODUCT CONTENTS Quantity 1 2 Description Ring Launcher including base and electromagnet with iron core Aluminum Ring Aluminum Ring with split Plastic Ring Coil with lamp Secondary Coil with 200 and 500 turns Connecting Wires for transformer demonstration Adjustment collar ASSEMBLY OF APPARATUS The only assembly required for the ring launcher is to place the adjustment collar on the electromagnet. See Figure 1. Figure 1: Adjustment Collar and Aluminum Ring WLS 804-45 CE1'CO Rmg Launcher Page
DESCRPTON OF USE/BACKGROUND NFORMATON The ring launcher is used to demonstrate some effects of electromagnetically induced currents and Lenz's Law. t consists of a vertically mounted solenoid of thick copper wire ( l) with a removable iron core composed of thin iron rods. The coil can be briefly energized with 110 VAC by pressing the LAUNCH button (2) on the control panel. For safety, an electronic circuit ensures that the coil is energized only briefly for each separate button press, no matter how long the button is held down. A variety of rings are supplied with the launcher. The rings fit over the top of the solenoid and are supported above the base by an adjustable collar (3). A solid aluminum ring, an aluminum ring with a split, and a plastic ring are included. Based on the type ofring used, the behavior of the ring changes when the coil is energized. This behavior can be explained using concepts of electromagnetic induction, including Lenz's Law. A coil of wire with a low voltage lamp attached is also included with the ring launcher. The transformer principle can be demonstrated by placing this coil over the solenoid coil and energizing the launcher. Figure 2: Ring Launcher with Secondary Coil and Connecting Wires for Transformer Demonstration Specifications: Overall height: 45.5 cm Power requirement: 110 VAC/60 Hz Fuse Rating: 250 V (30 A) Weight: 2.98 Kg Coil Dimension Diameter: 4.0 cm Length: 19.2 cm Coil with lamp: 10 turns Lamp: 5.1V/ 0.15 A Core Dimensions Diameter: 3.0 cm Length: 30.5 cm Ring Dimensions Diameter: 6.1 cm Width: 2.4 cm Thickness: 4.3 mm Secondary Coil 700 turns (200-0- 500) WLS 1804 45 CENCO Rmg Launcher Page2
Displays the voltage/current reading one data point at a time. Changes the displayed graph to current vs. time. Changes the displayed graph to voltage vs. time. Changes the settings when used as a transformer. This engages the built-in voltmeter. Energizes the electromagnetic coil. Figure 3: Control Panel The large display area on the front of the launcher shows a variety of useful information. When the LAUNCH button is pushed, a graph is displayed, that showing either the current or voltage output. A is the first point on the graph, B is the second point, C is the third point, etc. Each LED displayed on the graph represents 50 milliseconds, and the letter displayed on the upper left comer corresponds to the time interval value. n Figure 4, the voltage at position C represents the third 50-millisecond time interval; the voltage after 150 milliseconds is 34 V. The voltage graph is the default graph and will always be displayed first. Position C 34 v Figure 4: Voltage at Position C Pressing the CURRENT button displays the graph of the current vs. time during the launch in increments of 50 milliseconds. The UP button cycles through the graph so a current or voltage at a specific point will have its value displayed. n Figure 5, the current at position C, 150 milliseconds, is displayed....,... ':i....... -. ",,.......,... ~ Position C 11.5 A "l' -... t ~ ~4 ~~ ~ ~ 4~~~ ~ ~*~~~- ~~ u ~ ~ o~ ~~ ~~~4 ~ 0 ~ ~ '' ~<>." " ~*.. ~#.. ~.. it * &< t}~l;,\t'. lt "'"* " i.:i-1"~ ";;; ~.@;;;.;,<;\>... ~ c 4 ~ ~ ~ :t: <: '/j" '6- :.t '*Co~ Qi ~ i: ~ z, ~~ :: ::... ii ~~ ~ o~~ ~ ~z ~~ ~ ~ $ ~ ~- ~ -~~98D ~~- ~~~ ~ - ~~ 5D~~ ~~ ~ --~~~~Q~ ao ~ - ~* ~* ~~6 g ~ ~~--~ s a ~~ ~ ~ e 6 ~@~0 ~M~~~~ ~~~ ~ ~~~ 6 ~--~-~~~~-1~ ~ * ~ ~ ~ ~e + ~~ F 60~ b» me ~8~~-~-~~0-~~ ~~-~ P #c Figure 5: Current at Position C WLS804-t5 CE1'CO Rmg Launcher Page 3
The conventional explanation of the ring-launching phenomenon involves the induction ofa current in the aluminum ring placed around the energized coil, and invokes Lenz's Law to show that a repulsive force is generated. The explanation of the generation of an (experimentally observed) axially directed force is more complicated. The popular explanation will be given here, and for those inclined to dig deeper, an outline of the underlying physics with a reference for further study is given in the appendix. Popular Explanation When the complete ring is placed over the coil, with the iron core in place, and the coil is energized with an increasing AC current (-coil), shown in Figure 6, a large magnetic induction builds up on the axis of the coil. This changing magnetic induction (B-coil) generates a large induced current (-ring) in the ring. According to Lenz's Law, the current (-ring) tends to oppose the changes in B-coil, and so builds up an oppositely directed magnetic induction (B-ring). The repulsion between the two oppositely directed inductions drives the ring off the coil. Tt is clear that the key to this action is the induction of a current in the ring, and so, substituting a ring with a split in it to interrupt the closed conducting circuit should prevent the ring from being thrown off the coil. This is indeed observed. Similarly, using a non-conducting plastic ring in place of the aluminum one also shows no motion. Using the coil with the lamp demonstrates the existence of the induced current. When the coil is energized, the lamp will be illuminated. This demonstration can also be used to introduce the transformer principle. The main coil with many turns is energized by 0 volts and lights a 5.1 volt lamp using a coil of few turns. This small coil also experiences a force tending to throw it off the main coil, but the current developed is limited to a small value by the electrical resistance of the lamp and the force is too small to throw the coil off. B-coil Figure 6 -coil -ring B-ring Operation Safety To operate the launcher safely, the following precautions should be taken. 1. The launcher should always be plugged into a GROUNDED 0 Volt 60 Hertz outlet. 2. The launcher should never be operated in wet or damp locations. 3. Caution should be taken when operating this launcher near individuals with internal electromechanical devices, such as pacemakers. 4. Any damaged components should be replaced immediately. Always check components for damage before operation, particularly the power cord. 5. The launcher should always be used under adult supervision. 6. The current draw of this launcher can temporarily reduce the local supply voltage for other devices on the same power circuit. This can interrupt computers, televisions; stereos, etc. f possible operate the launcher on a separate circuit from these types of devices. 7. The ring is projected upwards suddenly with considerable force. Make sure that no person or object that could suffer damage is above the ring launcher when it is energized. Allow sufficient free height for the ring's trajectory. 8. Do not operate the ring launcher repeatedly without the iron core in place. Doing so can lead to overheating and a blown fuse. 9. When you are finished with the launcher, always be sure to turn off the power switch and unplug it from the wall outlet before storing it. Adjusting the Height of the Launch The height to which the ring is launched can be adjusted by moving the transparent adjustment collar up or down on the coil. Moving the collar up reduces the launch height, and moving it down increases the launch height. The minimum launch height is about m when the collar is flush with the top of the solenoid. The maximum launch height is between 4 m & 5 m, depending on the local power circuit. Note: when moving the collar down to increase the launch height, the collar must remain above the middle of the coil. f the ring is too low on the coil, it will not launch, but vibrates and quickly becomes hot. Below the magnetic midpoint of the solenoid assembly, the ring is forced downward instead of up. J M ore None Figure 7 WLS 1804-45 CENCO Ring Launcher Page4
Launching the Aluminum Ring. Place the ring launcher on a stable, level surface with adequate vertical clearance for the ring's flight. 2. To prevent accidental launches, remove the rings from the launcher before proceeding and make sure the power switch on the back of the launcher is turned off. 3. Plug one end of the power cord into the socket on the back of the launcher base, and then plug the other end into a grounded wall outlet. 4. Turn on the power switch on the back of the launcher base. The "OM Display" on the front display panel will show 000.0 V. 5. Slide the transparent adjustment collar onto the coil, leaving it close to the top of the coil. This will reduce the height that the ring will be projected. Place the ring over the coil so that it rests on the adjustment collar. Figure 8 6. MAKE SURE THE AREA ABOVE THE LAUNCHER S CLEAR. 7. Press the red LAUNCH button on the right of the control panel to energize the coil and launch the ring. The ring will launch and rise 1.5-2 m, depending on the position of the adjustment collar. 8. The display will show the voltage vs. time graph for 24 samples. With the help of the UP button, you can check voltage at any particular data point. For the example in Figure 9, C 034 V represents 3rd sample voltage. C represents sample number 3. Figure 9 9. Repeat the launch procedure using the split ring, and then the plastic ring to show that these do not launch. 10. Remove the iron core and attempt to launch the aluminum ring. The ring vibrates, but does not launch. This happens because the coil generates a much smaller induction without the core in place. t will also draw a much larger current because of its greatly reduced self-inductance. Repeatedly energizing the coil without the core in place will cause the coil to overheat and may blow the internal fuse. The Transformer Principle Demonstration Using the Coil with Lamp. Use the coil with the attached lamp. 2. Press the LAUNCH button and observe that the lamp illuminates as long as the main coil is energized. 3. Move the coil up and down in the solenoid and observe the variation in brightness of the lamp when the coil is energized. The maximum brightness is achieved at about the middle of the coil, where the magnetic flux change is strongest. Unlike the ring's failure to launch below the middle of the coil, the lamp will light at all points on the coil. Above the solenoid, the lamp will light weakly as long as the iron core intersects it. The magnetic induction falls off sharply beyond the end of the coil, reducing the induced current in the coil with lamp. WLS804-45 CENCO Rmg Launcher Page 5
The Transformer Principle Demonstration Using the Secondary Coil. Set up the secondary coil and the connecting wires as sho\.\t in Figure 0. Secondary Coil Connection to Built-in Voltmeter Figure 0: 200 turns 2. Press the TRANSFORMER ACTON button. The display will show the primary and secondary coil voltages, as below. ~';... l..... tt t<f tj j '.,-, f: K' ' -- '. ti~ ~ ffij?" ~-- 111 H.. -_ Figure 11: 200 turns or ~-,_ ~... rc... i.1 - t; ~ ~ >;) 1:-. lj......,,.. ' Figure 12: 700 turns :lt,,.. ' ~.., '" r..... 3. Because there is a built-in voltmeter, you could use any secondary coil you choose. Simply make the connections to the two banana plugs on the top of the launcher. WLS 1804-45 CENCO Rmg Launcher Page 6
Ba e Physics of the Ring Launcher The ring launcher is supplied with AC voltage; consider the first half of the AC cycle. During the first quarter of the cycle, the current -coil is increasing, and the field it produces is also increasing. This induces a current -ring in the ring that, by Lenz's Law, opposes this change. n Figure 13, the direction of -ring is clockwise when viewed from above and the ring is repelled upwards, as we expect. But during the second quarter of the cycle, the current -coil is decreasing, and so is the field it is producing, although it is still in the same direction. So by Lenz's Law, the direction ofl-ring is now counterclockwise, and the ring is repelled downward. The net effect in the first half of the cycle is,therefore, zero. The second half of the cycle results in a similar effect, but reversed in direction. So, by simple application of Lenz's Law, we should not expect the ring to move at all, just to vibrate! Figure 13 The actual effect is more complicated and was treated by S.Y.Mak and K.Young (AJP 54, 808, 1986). They considered the total field of the coil and the ring current together, and resolved it into an axial component Ba and a radial component Br. (Figure 13) The force on the ring is proportional to (-ring) (Br). But -ring is proportional to the rate of change of flux through the ring, dba/dt. f the field components Ba and Br were in phase, product (-ring)(br) would have an oscillating term in (sin t x cost t) which would average to zero, as we have seen in the simple analysis. But there is a phase difference 0 between Ba and Br, due to the non-zero inductance of the ring, L. This results in the average value of the product -ring. Br being non-zero, giving a net force. A second factor of comparable importance, which also contributes to the net force, is the variation of the phase difference along the axis, d0/dz. CARE/MANTENANCE OF LAUNCHER The ring launcher needs no special maintenance. With normal use, the unit will not overheat. However, excessive energizing without the iron core in place might cause the fuse to blow. f this happens, it will not display any data when the unit is plugged into a live wall socket. Replacement fuses are available at a local electronics store. The fuse is located within the round fuse holder on the back of the launcher. Make sure that the power button is 5\\itched off and the launcher is unplugged. Turn the fuse holder cap counter-clockwise to access the fuse. Your satisfaction is important to us. Call Cenco customer service for any concerns related to this product. Please do not return any apparatus until we have given you authorization. COPYRJGHT NOTCE The Cenco Ring Launcher operating instructions are copyrighted and all rights are reserved. Permission is granted to all non-profit educational institutions to make as many copies of these instructions as necessary as long as it is for the sole purpose of teaching students. Reproduction by anyone for any other reason is prohibited. Page 7
Steps For Use : 1. nsert the core. 2. Switch it ON. 3. Adjust height of acrylic pipe. 4. Step away from the unit. 5. Press the Launch button twice. & WARNNG DO NOT SWTCH ON OR USE WTHOUT RON CORE NSERTED Allow 10 MNUTES COOLNG TME after every 5 launches. DO NOT LEAN over the equipment while launching ---------- ---------- - -- ----- -