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615-4700 (10-155) St. Louis Motor

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615-4700 (10-155) St. Louis Motor ©2005 - v 8/05 615-4700 (10-155) St. Louis Motor DC Armature Assembly Knurl You May Need: Nut Attach 80-0105 Field Coil Assembly • Galvanometer Brush (Electromagnet Attachment) by South • Rheostat removing Pole Pieces and sliding North Pole • DC power supply, 6-12 volt bracket into Clip. Pole Product Description: The value of this motor lies in its open Activities design, allowing you to view and un- derstand the functions and relationships 1. Transformation of Electri- among the working parts of a DC motor. cal to Rotational Mechanical It has the further advantage of sharing Energy parts with 615-4705 Motor Generator. By You Need: Low Voltage Power Supply 2. Transformation of interchanging magnets from 615-4705 Apply 1.5 - 6 VDC to study the con- Rotational Mechanical to you build a motor with electromagnets. cept of the electric motor. Key compo- Electrical Energy nents, including the brushes, commutator, You Need: String, Galvanometer Warranty and Parts: windings, and magnetic field are seen in Wrap piece of string around axle We replace all defective or missing action. By switching the polarity of the of the armature, pull string to spin coils parts free of charge. For replacement part applied potential, you see the effects on within the magnetic field, thus inducing orders, we accept credit cards and school the fields created. a current. Attach galvanometer to your P.O’s. Products warranted to be free from See Worksheet #2. circuit to detect presence and amount defect for 90 days. Does not apply to ac- of induced current. Spin the coils in the cident, misuse, or normal wear and tear. opposite direction and note the difference in the induced current. Trace current flow through meter. What See Worksheet #1. happens when current is reversed? Why Accessories Recommended: may the motor need help to start? 80-0105 - Field Coil Assembly Pair Makes this motor function as an electromagnet. Connect to low-voltage 615-4065 Battery Kit - low-voltage DC power source. power supply with clip leads. 611-1045 Table-Top Pulley Assembly Tips: Diagram 1 To install electromagnet attachment, remove North and South pole pieces by sliding brackets out, slide leg “L” of Spin armature with string to Field Coil (electromagnet) bracket into induce current. slot of clip. To adjust, push in closer to armature or slide back. To adjust brushes, bend slightly if needed so they touch the Galvanometer armature. While brushes are tested in the factory, they may need further adjustment Diagram 2 Pull String due to shipping. SCIENCE FIRST® | 86475 Gene Lasserre Blvd., Yulee, FL 32097 | 800-875-3214 | www.sciencefirst.com | [email protected] SCIENCE FIRST® | 86475 Gene Lasserre Blvd., Yulee, FL 32097 | 800-875-3214 | www.sciencefirst.com | [email protected] ©2005 - v 8/05 3. Forces of Magnetic in series) or by connecting the potential Field Interactions source to a rheostat. (615-4065 Battery Kit recommended.) DC Power 1. Between Permanent and Electro- Supply The direction of the force on the magnetic Fields armature coil and thus the direction of A With two-pole armature in place and rotation may be determined by applying knowing the direction of the current, you DC the third left-hand/right-hand rule before Power A can apply either second left-hand or the current is actually passed through the Supply right-hand rule to determine the mag- coils. One could test this prediction by netic polarity of armature electromagnet. actually applying the current to the coils. Connected in series to 2 power supplies You can then predict how the magnetic with electromagnet attachment forces of attraction and repulsion will cause the armature to rotate. With the 3. Analysis of force applied to a cur- split ring commutator, the polarity of the rent carrying conductor in the current applied to the coils is reversed as presence of a magnetic field. the armature spins, causing a reversal in A To make more quantitative measure- the field produced. ments of the changes in the force on the These rules apply to determine the armature coils of the motor, attach a magnetic polarity of an electromagnet: string to the armature axle that runs over a pulley to a mass. (611-1045 Pulley rec- DC ommended) Time how long it takes the S N Power Electron Supply motor to raise the mass a fixed distance. flow Third Left-Hand Rule (You would actually be determining the power generated by the motor, which is directly proportional to the force it exerts.) P = W/t = Fs/t Second Left-Hand Rule Therefore, the shorter the time to Second Right-Hand Rule identical to left-hand rule except thumb points in raise the same mass a fixed distance, the direction of current (+ to -) greater the force the current carrying wire experiences due to the presence of a magnetic field. 2. Between two electromagnetic fields {with Electromagnetic Attachment 80-0105} Or eliminate rheostat and use a vari- Similar to example above, with use able number of batteries in place of String wrapped around axle of the left-hand/right-hand rule on both power supply electromagnet and coils on the armature. 4. Force on a Current 2. With a variable magnetic field Carrying Wire: F = B I l about the wire Requires 80-0105 Electromagnet Where F = force in dynes, B = magnetic Fixed distance Attachment field intensity in gauss, I = current flowing through wire, l = length of wire in magnetic While maintaining a constant current field. Force on wire is perpendicular to through the armature coils, the effects of Attach string to armature, pulley & mass magnetic field. how a varied magnetic field strength will 1. With current variable in the wire. alter the force experienced by a current By changing the current in the arma- carrying conductor. Again, the current For Shunt Motor You Need: ture coils, you can demonstrate that the may be varied by changing the number force on a current carrying wire is pro- of dry cells applied in series to the elec- • 6 clip leads portional to the current passing through tromagnet attachment, or by using a • electromagnet attachment. that wire. As the current is increased in constant power supply connected in series Attach one positive (+) end of battery to both front terminals & one brush. the armature coils, a greater force causes with a rheostat and the electromagnet Attach negative end (-) of battery to the armature to spin faster. The current attachment. The difference in the force both rear terminals (of electromagnetic in the coils can be changed by changing applied may be seen by the speed of the attachment); other brush. the applied potential (1,2,3,4 dry cells armature’s rotation. SCIENCE FIRST® | 86475 Gene Lasserre Blvd., Yulee, FL 32097 | 800-875-3214 | www.sciencefirst.com | [email protected] SCIENCE FIRST® | 86475 Gene Lasserre Blvd., Yulee, FL 32097 | 800-875-3214 | www.sciencefirst.com | [email protected] ©2005 - v 8/05 5. Electromagnetic Induction case of varied magnetic field strength, in a Conductor String wrapped the armature coils must be turned at the A. Direction of induced current as around axle same rate for each trial. This may be conductor moves through mag- more easily achieved by using the pulley netic field. system with the same mass for each trial. 1. This can be predicted again by ap- See Worksheet 3. plying the third left-hand/right-hand rule to find the direction of the force Variations include: on electrons in the conductor. 1. Replacing accessory electromagnet, 2. Can be demonstrated by connecting power supply and rheostat with a the motor, now acting as a generator, Fixed distance, in series with a galvanometer. Deter- varied mass varied number of batteries. 2. Pulling the string out from the mine polarity of induced current by Pulley regulates speed at which string armature axle by hand each trial at spinning the coils in each direction. is pulled B. The magnitude of the current in a constant rate in place of the pulley conductor is proportional to the system. velocity at which conductor moves C. The magnitude of the cur- through magnetic field. rent induced in the conductor is 6. Induced Electromotive proportional to the intensity of the Force on Existing Current Can be demonstrated by connecting the magnetic field that conductor is A current induced by the motor, act- motor, acting as a generator, in series ing as a generator, can have different with a galvanometer and winding a string moving through. (Requires accessory electromagnet) effects on an existing current depending around the armature axle. upon the direction of the current induced Vary strength of magnetic field by: by the generator. 1. Connecting a rheostat in series with This can be demonstrated by connect- 1. Pulling the string by hand at a constant a power supply to the accessory elec- ing the motor in series with battery and rate for several trials with different tromagnet. By changing the current to small light bulb. When the circuit is com- rates will show an induced current on the electromagnet, the magnetic field pleted, bulb will light. By spinning the the galvanometer proportional to the intensity will also be varied propor- armature in either direction, the effects rate at which the string is pulled. tional to that current. of the induced current can be seen by 2. Utilize the pulley to regulate the vari- 2. Connecting different numbers of the brightness of the light. If the induced ous rates by placing different amounts batteries (1,2,3,4) in series to the current opposes the direction of current of weight at the end of the string which accessory electromagnet, thus vary- supplied by the battery, the light dims.
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