615-4585 (10-110) Electromagnet Kit (Gilley Coil)

as a result of the approach or departure Warranty Background Ideas of a magnetic field or as a result of We replace all defective or and Concepts for the strengthening or weakening of a missing parts free of charge. Ad- stationary one. The flow depends on ditional replacement parts may be Experiments change. ordered toll-free by referring to the An electric current is a flow of In Experiment 3, iron filings are part numbers above. All products electrons. The cause of electron flow used to outline magnetic lines of flux. warranted to be free from defect can vary. They may be made to flow If we move a magnet towards a coil for 90 days. Does not apply to due to electrostatic attraction or repul- (as in Experiment 1), the flux linking accident, misuse, or normal wear sion. Electrons in metallic substances with the coil is increased. During that and tear. are quite mobile and can be induced time when the magnet is approaching to flow by the presence of amagnetic the coil (i.e. flux is changing) an EMF field. is induced in the coil. The magnitude It is not fully understood what a of the EMF depends on how fast the magnetic field is. We describe it in flux is changing (i.e. how fast the mag- Introduction terms of its effect on materials. net is approaching.) The magnitude This apparatus is used to of the EMF can be calculated using Faraday's Law. demonstrate induced currents. It The following properties apply consists of two coils, each 210 to magnetic fields: 1. Electrons flow only at right angles Avg induced EMF = Nd volts turns of #20 gauge copper wire and 1.01 dt various soft iron magnetic cores. to the direction of the magnetic field. The coils are mounted in plastic 2. The electromotive force (EMF) N = # of turns in coil saddle blocks enabling them to is a measure of a source's ability d = change in flux stand vertically. to cause a current to flow in an dt = change in time No assembly is required. Indi- electrical circuit. The pressure, Another important idea in Experi- vidual setups are outlined in each or EMF, of the electron flow is ment 1 is Lenz's Law. Lenz's Law experiment. proportional to the rate of change of states that the EMF induced in a coil the magnetic field. acts to circulate a current in a direc- 3. The number of electrons which tion which opposed the change of respond to the push of the magnetic magnetic flux which gave rise to the field depends upon the resistance of induced EMF. the electric circuit including the coil In other words, any changes are Other Materials and the counter EMF generated by opposed. Therefore, when we move a this flow. magnet (N-pole) towards a coil (as in Needed Figure 1a), then the flux entering the • 6 volt (or greater) battery left end of the coil is increased. Ap- or Magnetic Flux plying Lenz's Law, the polarity of the The next basic concept necessary EMF produced in the coil must cause a • Power supply exceeding in understanding the idea of induction current to flow in the coil such that the 1 amp DC is magnetic flux. In order to induce a flux produced by the coil opposes the coil, we need a in flux. change flux entering the coil. Magnetic flux is related to the num- In Experiment 2, one coil is used ber of lines of magnetic force either en- to induce another. When two coils are P/N 24-0110 tering or leaving a magnetized surface. magnetically coupled, the coil which © Science First/ Morris & Lee Inc. A magnet with a strong magnetic field Science First is a registered is responsible for producing the flux produces more lines of flux than does a trademark of Morris & Lee Inc. all is knows as the primary winding. The magnet with a weak field. It is immate- rights reserved. winding which receives energy is rial whether the magnetic flux changes known as the secondary winding.

What is an Objective: same direction as that caused by the • To demonstrate magnetic induction approaching N-pole in Step 1, thus Electromagnet? • To show the direction of current creating an electromagnet. A current carrying wire can be flow and its potential Next, bring the N-pole of the bar looped to form a coil. The coil is • To create a simple electromagnet magnet towards the coil. called a solenoid. By placing a soft Does the new magnet attract or iron rod in the core of the coil, we cre- Procedure: repel the approaching N-pole? ate a magnetic field around the coil. Connect one coil to terminals of a Explain your answer. The coil along with its iron center galvanometer as shown in Figure 1a. create what is known as an electro- 1. Move the N-pole of the bar magnet magnet. towards the coil center. Note the Results for Experiment 1 The strength of an electromagnet direction in which the galvanometer depends upon the number of turns (N) needle moves. Step 1 & 2: Direction of Current in its coil and the material that coil 2. Repeat with a departing N-pole, and core are made of. An electromag- approaching S-pole and departing Pole & Direction of Direction of net is a temporary magnet. One benefit Direction of Needle Current S-pole. Record your results. Magnet Deflection of a magnet of this type is that the 3. Using the n-pole of the magnet, magnetism can be controlled. When N approach Pointer right Clockwise bring the magnet towards the coil N depart Pointer left Counterclock the current is shut off, the electromag- first with a slow approach/departure S approach Pointer left Counterclock net loses most of its magnetism. and then with a fast approach/ S depart Pointer right Clockwise In Experiment 4, we create an departure. In this case we wish to electromagnet and demonstrate its observe the distance that the pointer Step 3: Direction of flow lifting power. moves. This shows the intensity of flow or potential. Additional materials are required. Step- 4. Knowing that the flow (flux) by-step procedures and results accompany will continue only as long as the each experiment. magnetic field is changing, what

would you expect to happen if the Approach Fast

Slow Approach Slow

magnet were to remain stationary: Initial Pointer Experiment 1 a. To check your result, bring either Magnetic Induction end of the magnet towards the coil in a Coil center and record the deflection of the needle after a few seconds. Approaching N-pole Materials Needed: Compare your expectations with • One coil the actual outcome. • One bar magnet 5. To form an electromagnet: • Galvanometer Connect the coil to the battery as • 9V battery shown in Figure 1b. This will • Two (2) clip leads (included) Initial Pointer

cause the current to flow in the Approach Slow Fast Approach Fast

Figure 1a Departing N-Pole

Step 4: With a stationary magnet, the change in flux = 0. We would expect no deflection in the needle. Note that Figure 1b this idea corresponds to results in Step 3. The slower approach or departure of the magnet caused a smaller deflection of the needle. A stationary magnet would cause minimum or (zero) movement.

Step 5: Experiment 2 Experiment 3 Because electron flow from the Primary/Secondary Coil Magnetic Lines of Force battery is running in the same direction as the electromagnet, it will repel the approach of the N-pole. ("Like" things Materials Needed: Materials Needed: repel.) • Galvanometer • One coil • Two (2) coils • 2 half-round bars • Battery • Stiff paper • Four (4) clip leads • Iron filings • Iron core • Battery Questions: • Two (2) clip leads 1. What is the source of energy which Objective: caused the current generated in • To demonstrate mutual induction Objective: Steps 1 and 2? • To outline the magnetic field 2. What determines the amount of Procedure: generated by the current flow. current generated: 1. Connect primary coil (A) to a 3. How long does the induced current battery and the secondary coil (B) Procedure: last? Why? to a galvanometer (Figure 2). The 1. Place a half round bar through 4. What determines the direction of terminals for each coil should face one coil flat side up. the induced current? opposite directions. Place the plastic card over the coil 2. In what direction does the and rest it against the half round galvanometer needle deflect? In iron bar. Lay the second half round Answers to Questions: what direction is the flow in the bar on top of the plastic card and 1. The source of energy which caused second coil, Coil B? Knowing that slide it through the coil center. the current generated in the coil is electrons flow from the negative This secures the coil. Figure 3a. the magnet. electrode of a battery, in what 2. The amount of current generated direction is the flow of Coil A? Is depends on the speed at which the flow in each coil the same or the electrons are flowing (i.e. how different directions? Why? Figure 3a fast the magnet is approaching or 3. Separate Coil A from Coil B by departing). 2 or 3 inches. Quickly bring Coil 3. The induced current does not last A towards Coil B and observe the very long. There is only current galvanometer. Does the approach of when flux is entering or leaving Coil A give the same direction of the coil. Once the magnet becomes deflection as seen inStep 2? Why? stationary, the induced current 4. Repeat Step 3 with a departing stops. primary coil, Coil A. 4. The polarity of the magnet 5. Of the procedures 2 and 3, which determines the direction of the generates a higher potential? induced current. 6. Repeat Step 2 using an iron core 2. Sprinkle iron filings on the plastic through the center of the coil pair. card. For best results, scatter the Record the degree of deflectionof filings over the entire card. the galvanometer when the battery 3. Connect the coil to the battery is connected and then discon- terminals (see Figure 3b) using two nected. Does the quantity of of the clip leads. magnetic flux increase or decrease when an iron core is used?

Figure 2

Figure 3b

4. Tap the card lightly. Observe the polarity in each core end. pattern which the filings create Experiment 4 5. Remove either coil and reverse (See Figure 3c, below.) Electromagnetism the direction of the current. (That is, return the coil to the U-shaped core now facing the same direction Materials Needed: as the other coil.) Test the lifting Figure 3c. • Two coils power as before. • U-shaped core 6. Which magnet was stronger? Why? • Battery • Three (3) clip leads • Flat core • Magnet or compass How To Teach With • Two (2) hex nuts (included) Electromagnet Kit Concepts Taught: Solenoid; Am- Objective: pere's Rule; Electromagnetic attraction • To create an electromagnet and test and repulsion; Magnetic permeability; its lifting power Electromagnetic polarity; Flux density; Mutual inductance (transformer effect); Procedure: Induced current and induced magnetic 1. Place the two coils on each end of field. the "U"-shaped core as shown in Curriculum Fit: PS/ Electricity and Note that lines of magnetic flux never Figure 4, below. Magnetism. Unit: Moving Charge and intersect each other! [Note: Coil terminals face opposite Magnets Grades 9-10 directions.] More Experiments Secure coils to each end of the Illustrating Magnetic Lines of U-shaped core by screwing on two hex-shaped nuts provided. Force Related Products 2. Complete the series by connecting The following products can be ordered from 1. Repeat above procedure with both one terminal of each coil to a your distributor, or, if unavailable, from coils close together and current battery and the two remaining manufacturer Science First. flow in thesame direction - and terminals to each other using 3 clip then in opposite directions. • 615-0300 Lifting Magnet - leads. See Figure 4. 2. Repeat above procedure without Weights two pounds, lifts two 3. Test the lifting power of the using the iron core. How does the hundred pounds. Striking display of magnet by grasping the U-shaped pattern differ from your results in electromagnetic power. Precision ma- core and trying to lift the flat core. the original experiment? Why? chined magnet with alligator clip leads [Note: The coils may move around and battery holder, instructions. Needs on the U-shaped cores as you lift 1 1/2 volt D cell battery. it. Their position is irrelevant. Our • 615-4650 Primary Secondary Coil - demonstration only shows that the Excellent for electromagnetic core becomes magnetized.] induction and transformer effects. 4. Use a compass or magnet to test the Contains two coils, both with bind- ing posts and plastic mounts. Soft iron keeper and instructions included. Needs voltmeter. Figure 4 • 615-4685 Toy Motor Kit Construct a working DC motor at a price your entire class can afford. All parts provided, including two coils copper wire; base; field pole; armature core; brushes; all fasteners, battery clips, instructions. Needs AA battery.

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