Unit 7. Magnetism. The North end of a compass or any magnet is the end, and is called the. The South end of a compass or any magnet is the

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1 Unit 7 Magnetism Origin of the term magnetism The Ancient Greeks discovered a mysterious mineral which attracted, and would point if it were allowed to rotate freely. This mineral was found near a place called, in Greece, hence the term. This mineral later became known as because it always pointed towards the leading, or "lode" star. Today this star is called the. Definition: North and South Poles The North end of a compass or any magnet is the end, and is called the. The South end of a compass or any magnet is the end, and is called the. Properties of Magnets Like Poles Different Poles 1 P a g e

2 Magnetic Field Around every magnet there is a field of force It acts at a - similar to field or field. The direction of the field lines is given in the way that a would point. The lines point from the North end of the magnet and the South end. When drawing magnetic fields, remember that the field lines never and are to the surface. Draw magnetic fields around the following: N S N N S 2 P a g e

3 S S N Earth's Magnetic Field The earth's magnetic field enables people to navigate using a. It is believed that certain animals have a magnetic sense of direction which enables them to navigate. It protects us from harmful by deflecting them into outer space. Provides us with entertainment. It produces the and What causes the earth's magnetic field? It is believed that it results from the motion of (mainly molten ) in the liquid outer core of the earth. 3 P a g e

4 Magnetic field reversals Reversals have been documented as far back as million years. During that time more than reversals have taken place, one roughly every years on average. However, the time between reversals is not constant, varying from less than 100,000 years, to tens of millions of years. Many authors have pointed out that the dipole part of the magnetic field has been during historic times, and that if the present trend continues, the dipole field will go to in roughly years. Some people take this to mean that we are entering a. Although this possibility cannot be discounted, many investigators believe that the trend will not continue and that the field will, as it has many times in the past. 4 P a g e

5 Magnetic Declination: North and North are not in the same place. Magnetic north is near. The angle between the geographic north pole and magnetic north is called varies from place to place and from year to year. 5 P a g e

6 To use a map and compass you must declination to your compass bearing to get true north. The link below shows how to use a compass field/compass_e.php Magnetic Deviation: In a vehicle such as a ship or aircraft, a compass is influenced by the magnetism of the used in the construction of the vehicle as well as the Earth's magnetic field. This causes the compass needle to point in the. This directional error is called ". Many people incorrectly use deviation when they mean declination. Magnetic Inclination (or Magnetic Dip): It is the of the earth's magnetic field. 6 P a g e

7 It is the between the magnetic field and a horizontal line at any point. It is measured with a which is basically a compass that is suspended vertically at its centre of mass. Question: What direction will a magnet point if it were suspended vertically at its centre of mass at the following places? A) magnetic north B) equator C) magnetic south D) in our classroom 7 P a g e

8 Types of magnetic substances: substances are attracted by magnets. They can become strong induced magnets when placed in the of another magnet., and their are magnetic. substances are attracted by very strong magnets. are magnetic substances. substances are by strong magnets. are magnetic. Magnets and Magnetic materials A is an object composed of magnetic material that is. made from material A material is one that is by the force of magnetism. Made from material 8 P a g e

9 Question: Assume that you are given a bar magnet and an identical looking object. Describe how you would determine whether or not: A) The object is magnetic B) The object is a magnet Domain Theory Suppose we take a bar magnet like the one below and break it into 2 equal pieces. Each piece will act like a bar magnet If we do this again we get: If we continue to an atomic level you would discover that each atom acts as a. We call each atom a. 9 P a g e

10 A number of these dipoles can act on each other so that they all have basically the same This area is called a. A ferromagnetic substance that has never been close to a magnet will have its domains If such a substance is placed in a magnetic field the domains will start to with the. The the field, the alignment will take place. If the external field is, then over a period of time the domains of the substance will also direction. The induced magnetic poles of the ferromagnetic substances will 10 P a g e

11 Magnetic Induction Magnets can be made by stroking a ferromagnetic material, such as a nail or needle, with another magnet. It can also be done with a hammer! How? Magnetic Saturation Keepers for Bar Magnets Prevents the bar magnets and horseshoe magnets from losing their. What type of material is used for keepers? Reverse Magnetism This occurs when a magnet is exposed to a stronger magnetic field, that is in orientation, over a period of time. Why shouldn't a compass be transported in a gun case? 11 P a g e

12 ELECTROMAGNETISM The study of the relationship between electricity and magnetism is called Before, it was believed that there was no connection between electricity and magnetism. Who discovered the connection? Although magnets receive a lot of exposure, we use and depend on much more in our everyday lives. Electromagnetism is essentially the foundation for all of. We use electromagnets to: Electromagnetism works on the principle that an. This magnetic field is the same that makes metal objects stick to permanent magnets. In a bar magnet, the magnetic field runs from the pole. In a wire, the magnetic field forms the wire. 12 P a g e

13 Magnetic fields are generated by moving electric charges. wire The direction of the around a carrying conductor can be found using the first Left Hand Rule. First Left Hand Rule. The thumb points in the direction of the. The fingers wrap around the electron flow in the direction of the. 13 P a g e

14 NOTE: There are right hand rules: These work for. Recall that is the of electron flow. The is still in the same direction. Example: Draw the magnetic field around the following 1. A) e - B) C) out in 2. At each point labeled below on the circuit. A C B 14 P a g e

15 3. Which way would a compass point in the circuit below? 4. Indicate the direction of the electron flow in each of the following: A) B) C) Page 638 #1, Page 663 # P a g e

16 Magnetic Fields in a Curved wire or in a Loop. Draw the current and the magnetic field around the cross section of the loop of wire as shown below back wire front wire What do you notice? Looking from the bottom: 16 P a g e

17 We can apply this to a series of loops wrapped around a toilet paper roll. Draw the current on the front of the loops. Now imagine that we cut the loops as below. In your mind's eye, discard the half of the coil nearest you and draw the magnetic field around the cross section of the loop of wire as shown below. Top wire Bottom wire What do you notice? In fact a series of loops provide a magnetic field similar to one found in a bar magnet. 17 P a g e

18 Second Left Hand Rule The direction of this magnetic field in a coil is determined by: wrapping the of your left hand around the coil in the direction of the. the points in the direction of the inside the coil. (The thumb is the pole of the magnetic field) Page #2,3 18 P a g e

19 Note: A large number of loops can be classified as. flowing through a coil produces a. This is how are produced. Magnetic field strength is measured in a unit called Most classroom magnets are The earth's magnetic field is Junkyard magnets used to pick up old cars produce fields of about. Factors Affecting the Magnetic Field of a Coil. (page 636) The strength of the electromagnet can be increased by: increasing the in the coil increasing the of coils. The more the coil is, the stronger will be the field. decreasing the of the coil. A smaller results in a stronger magnetic field. The more the material within the coil, the greater the magnet s strength. The reason is that the within the ferromagnetic core line up due to the magnetic field passing through the centre of the coil. The fields associated with the domains then the applied field. 19 P a g e

20 Would you use soft or hard ferromagnetic material? The best ferromagnetic core is because not only do the domains line up when the current is flowing, they also go back to their when the current is shut off. Why is this an ideal control condition for a magnetic crane that moves car wrecks from one location to another? What is a special term that accounts for the change in the strength of an electromagnetic according to the type of material that comprises the core? Note: You can think of permeability in a general way. For example, a is not very permeable as far as is concerned, but a is very, very permeable! So, too, some materials are very permeable as far as are concerned. are examples. And, as you know, have very little permeability for magnetic lines. So, it is easy to compare substances according to how well travel through them. 20 P a g e

21 You could even say the magnetic lines are " very well in substances with permeability. The of a substance is a of the of the magnet when the core is made of that substance to the when there is at all ( ). substances have a high permeability. You can find the magnetic permeability of some familiar substances in Table 15.3 on p. 637 of your textbook. However, here is a cautionary note: the permeability coefficients in the table are not values, but rather appear to be permeabilities. Notice that µ for a vacuum and oxygen (and you can assume also for air) is taken to be. For iron, µ is given as, which we should interpret to mean that if an core is place inside a coil, the magnetic field strength of the coil will increase by a factor of. By what factor would the following increase or decrease the magnetic strength of an electromagnet with an air core? A) An iron core B) A core of aluminium C) A core of copper 21 P a g e

22 Magnetism (Revisited) The Nitty Gritty of Magnetism What do electrons have around them when they are still? What additional field do electrons have around them when they are moving?. Are the electrons moving in an atom or are they sitting still?. Since the electrons are moving, what can we say about the atom? What is the word for such a tiny magnet? 22 P a g e

23 Is this magnetic effect the same for all materials? As you can see from the picture, a couple of electrons in the same region can have a effect if they rotate in ways. That is, if one rotates while the other rotates, there will be a effect on the. How does the different possibilities for electron movement affect the magnetic nature of materials? Some materials are by a magnet, some are, and some are even if the magnet is strong enough. substances are attracted by a magnet. In such substances the spin of one electron is by another. If paramagnetic substances are strongly attracted, they are given a special title, 23 P a g e

24 What are some ferromagnetic substances?. Other paramagnetic substances that are attracted to a lesser degree are: What is the name given to substances that are repelled by a magnet? WHY are they not magnetic? In some substances electrons are paired in such a way that the of one. Examples are: A cautionary note: Some textbooks state that the term is applied only to substances that experience a attraction to a magnet. In this view is not under the umbrella of paramagnetism, but instead is a separate category. 24 P a g e

25 Motor Principle motors may look complicated when you look at them (don't dismantle Mom's mixer!), but the underlying principle is as simple as this: if two magnetic fields are in the same vicinity, they will on each other. Depending on how they are brought near, their magnetic fields either each other, or each other. That is, one magnet can make the other. This is the basic operation of a! If the inside part is then connected to beaters, you can make a If the inside part is connected to a saw, you can cut a. Who first devised the first motor that produced continuous motion using a form of energy? What was the energy? When was this? Basic Idea: A carrying conductor placed in a field experiences a. WHY? Consider the following: In the picture below you can see only one magnetic field. There is no sign of a circular field yet. This is because the switch is. 25 P a g e

26 There is no flowing, and no circular field around the straight conductor which is hanging like a motionless swing. Below shows what happens when the switch closed. In this picture the switch is closed (i.e., the motor is turned on), the current flows and a circular magnetic field is created around the conductor according to left-hand rule. Look at the two magnetic fields to the left of the conductor. 26 P a g e

27 . This means the two fields are each other to the left of the conductor. WHY?! The magnetic fields to the right of the conductor are in directions. Here the fields are each other. WHY? The end result is that the conductor is kicked to the. We have made out of electricity and magnetism! Example: Determine the direction of the wire below. Two magnets are aligned as shown and the circle represents a current carrying conductor. N S Hint: Draw the magnetic fields. What do you notice? Which way will the wire move? Rather than have to draw the magnetic fields each time, we can determine the direction of movement of the wire by the, yet again, another 27 P a g e

28 Third Left Hand Rule: With an opened left hand The thumb points in the direction of the The fingers point in the direction of the The palm faces the direction of the applied to the wire. (Notice the 3 right-angles) Example: Determine the missing force, electron flow, and poles. A) B) C) S N 28 P a g e

29 That magnetic swing was not much of a motor. However, can you remember being in a swing with someone you really hard? Were you ever scared that the swing would make a and come down on the other side? If we had the right set-up, the magnetic fields could make the straight conductor do that. This would result in motion, which is the motion that all make. If you have ever taken a motor apart, you know that the inside piece that rotates consists of many, many turns of. This is too complicated to draw here, but we can show why the " rotates by looking at just one of the turns of wire. Single loop motor "g and "h" are. "e" and f make up a with a halfring attached to each end of the loop inside the motor. The brushes allow the to pass into and out of the loop via the split rings. 29 P a g e

30 Apply the third left hand rule to both sides of the wire. Since the left-hand side is moving, and the right-hand side is moving, the loop (when properly mounted on bearings) will. Now, this is more like a! Not much has been said about the split-ring commutator. It is a simple but necessary device for a. (DC means - that is, current which travels in ). What can you say about the current in the loop when the loop has rotated 1/4 of a complete rotation from its present position? Will the loop stop after making 1/4 turn? Is the inertia required to make the loop rotate very far? How come? Because almost immediately split ring comes in contact brush, and split ring comes in contact with brush. When that happens, the flows in the loop once more. What fascinating thing has happened to the current in the loop? 30 P a g e

31 When the loop started, "e" was in contact with "g" and "f" was in contact with "h". (Look and see.) That meant that the current entered through split ring _" and left via split ring _". After ¼ turn the current is entering via split ring _" and leaving via split ring _". Since the half rings are to the ends of the loop, the current in the loop has. Why is it important for the current to be reversing? It is only in that way that the left hand side of the loop will always be forced, and the right hand side of the loop always forced 31 P a g e

32 Formula for Magnetic Force Note: If a wire, or conductor is parallel to the magnetic field, the wire experience any. On page 641 there is a formula for calculating the force produced on a current carrying conductor by the motor principle F- B I L - angle made between and If = 90 o then, which will produce the force. Conductor is to magnetic field If = 0 o then, which will produce NO force. Conductor is to magnetic field 32 P a g e

33 What are the units for T? Solve the equation for B. Sub in the units. The unit for B is named to honour the Croatian-born, American engineer, ( ) is the magnitude of the magnetic field strength that causes a conductor of length to experience a force of when the conductor is carrying a current of and is to the magnetic field. Practice: 1. Calculate the magnitude of the force on a 2.1 m wire that is carrying a current of 5.0 A perpendicular to a magnetic field of strength 1.4 x 10-4 T. 2. The wire (and current) in practice exercise 1 is running from east to west. The magnetic field direction is from north to south. In which direction will the force be exerted on the conductor (ignore gravity). The net force on the conductor in this case will be 33 P a g e

34 3. Determine by what factor the force diminishes if a conductor changes its orientation from being perpendicular to the magnetic field to a new position that makes an angle of 45 o with the field. 4. A certain current-carrying conductor which is perpendicular to a magnetic field experiences a force of magnitude F 1. If both the current and length of the conductor are tripled, but the conductor moves from a perpendicular orientation to an angle of 30 o with the field, the new force is F 2. Compare the magnitudes of the forces. 5. A 3.0 m wire has a linear density of kg/m. The wire is sitting in a magnetic field of strength 3.5 x 10-3 T and the wire is perpendicular to the lines of force. How large a current would be required in order for the wire to be suspended against gravity in the magnetic field? In your textbook: on p do #1, #2. on p do #10, #11. on p do #25, #26 on p do #37 34 P a g e

35 Other Formulae for Electromagnetism Biot's Law. Biot's Law states that the magnetic field strength is directly proportional to the in a straight conductor, and to the perpendicular distance away from the conductor. The constant of proportionality being, where the is the of the substance in which the field is located. NOTE: If the field is in free space, the µ is written as where (where T = tesla, m = metre and A = ampere) can be considered to be free space. Mathematically: This law is attributed to Jean-Baptiste Biot ( ). Practice 1. Find the magnetic field strength (B) in air 7.0 mm away from a straight conductor in which there is a current of 2.0 A 35 P a g e

36 2. When a potential difference of 12.0 V is applied to a straight conductor, the magnetic field strength (B) 2.0 cm from the conductor is 3.0 x 10-5 T. What is the resistance of the conductor in ohms? 3. Two parallel wires each carry 5.0 A of current in opposite directions. A) Which way are the wires forced to move? B) What is the magnetic field strength midway between the wires if the wires are 10 cm apart? 36 P a g e

37 4. Repeat practice exercise #3 with the current in the wires running in the same direction. Solution: 5. Two 1m parallel wires each carry 1.0 A of current in opposite directions. What is the force that acts on one of the wires? 37 P a g e

38 6. How far from a conductor carrying 5.0 A of current is a second wire with a current of 10.5 A if the force between the two wires is 2 x 10-5 N/m Magnetic Force on Moving Charges Thus far, we have been saying that the force on a current-carrying conductor in an external magnetic field is The key phrase here is. If there were no, there would be no on the conductor So, the force is really exerted on the. The conductor provides a for the current. 38 P a g e

39 If a stream of were shot through a magnetic field the force on the stream would still be, where, in this case, L would be the length of the that falls within the magnetic field. To simplify things, instead of picturing a of electrons passing through a magnetic field, imagine a single electron,, being fired into the field. Of course, the single charge,, doesn't have to be an electron. It could be a. If q is traveling at a speed v and takes a time of t to travel a distance L, what is the relationship between L, v and t? Think back for a moment to a stream of electrons. If there are n charges of size q in the stream, what is the total charge (Q) in the stream? Think back even further to the expression for current, I. How did we write it? Write an expression for I by using nq and t. Use this expression above and L = vt to re-write F = BIL sin. 39 P a g e

40 The previous expression gives the force on charges. But we are looking for the force on a single charge, that is, n=1. The expression becomes where _ is the magnetic field strength in _ is the magnitude of the charge in that is moving at a velocity in, and is the angle between and Direction of the Force To determine the direction of the force on a charge that is passing through a field, just apply left-hand rule #3: Point your fingers in the direction of the field, your thumb in the direction that the is moving, your palm points in the direction of the on the charge. While the left hand rule will work to show the deflection of a stream of electrons, the will be useful for a stream of positive particles. 40 P a g e

41 Example: 1. A magnetic field of 44.0 T is directed into a computer screen. A particle with a negative charge of 2.0 x C is shot into the field from the right, making an angle of 90 o with the field lines. If the particle is moving at 5.4 x 10 7 m/s, what magnetic force does it experience? p do #6--#8. p do #12, #14 p do #31 41 P a g e

42 More fun stuff! If a charge is shot in horizontally (or perpendicular to the lines of force), it will follow a path. This is because the moving charge has a circular field around its direction of motion. This field and the permanent field reinforce each other on one side of the charge, therefore forcing it into circle. N - Pole N - Pole e e S - Pole S - Pole Electron shot in to magnetic field Electron shot in to magnetic field What would happen if the charged particle was a proton? N - Pole N - Pole S - Pole S - Pole 42 P a g e

43 Describe the behaviour of beams of charged particles passing through a magnetic field. N - Pole e S - Pole Centripetal Magnetic Force For a particle moving at a speed and experiencing a constant at to its traces a. What is providing the force? The force is. 43 P a g e

44 Example: An electron is shot perpendicularly into a magnetic field of strength T with a velocity of m/s. What is the radius of the electron s path inside the magnetic field? Review example 8 page 654 A) What is the velocity of an alpha particle moving in a circular path of radius 10.0 cm in a plane perpendicular to a 1.7 T magnetic field? Solution: An is a particle consisting of two and two that is identical to the and is emitted during certain. What is the charge on an alpha particle? 44 P a g e

45 B) If this alpha particle is accelerated by the application of an electric field over a set of parallel plates, what voltage is required to accelerate the alpha particle from rest? Recall: and Kinetic Energy is given by Page 665 #28,29,30 45 P a g e

46 ELECTROMAGNETIC INDUCTION Recall Oersted's principle: when a current passes through a straight conductor there will be a around the conductor. discovered an exactly opposite phenomenon: when a moves near a conductor it makes any free charge in the conductor move. This means a magnetic field creates a. Faraday's law of electromagnetic induction Whenever the in the region of a conductor is moving, or in magnitude, are induced to flow through the conductor. The most critical word in in Faraday's Law is the word. If the magnetic field is not there is It is important to realize that a magnetic field can change in two ways: It can move. This can also happen in two ways: 46 P a g e

47 o moving a back and forth, moves its back and forth o the magnetic field can remain while the is moved back and forth by some outside A magnetic field can also change by having its increased or decreased. This is most easily done with an since all one has to do is increase or decrease the through the coil. DEMO 1. Determine what happens to the Galvanometer in each of the following: A) A wire is connected to a galvanometer and then passed through the poles of a horseshoe magnet. o The needle will and then back to. o When the wire is move out of the poles the needle will and then back to. B) A bar magnet is inserted into a coil of wire which is attached to a galvanometer. o The needle will and then back to after the bar magnet stops. o When the bar magnet is moved out of the coil the needle will move in the and then back to. 2. What affect does more turns have on the magnitude of the induced current?. 47 P a g e

48 3. What affect does the relative speed between the coil and the magnet have on the induced current?. 4. A) How can the magnetic strength of the bar magnet be increased? By increasing the, and the poles in the same direction. B) What is the effect on the induced current of increasing the strength of the bar magnets?. What are the factors that the induced effects are affected by? (i) the number of in the coil (ii) the between the magnetic field and the coil (iii) the of the magnetic field (iv) the of the magnetic field NOTE: The orientation of the magnetic field determines the that the induced current will travel. Direction of the Current: The following pictures show a conductor being pulled into the screen (paper) with external magnetic field and power source. 48 P a g e

49 Next we make the conductor through a magnetic field. Note that this is the same as if the conductor were and the magnet was. Thus, to the conductor, the magnetic field is changing. According to a current will be induced in the conductor,. You can see the circuit because there is a wire attached to the ends of the conductor. The next picture shows why the current is induced as explained by Faraday. 49 P a g e

50 The very important thing to keep in mind is this: either the must move, or the must move, or the must in in order for current to be. If the conductor just sits in the field, there will be current produced. Somehow, the conductor must the lines of force. You should realize that this is a marvelous discovery. We can produce electricity without have a in the circuit. All we need is between a and a in a closed loop in the field. What if the conductor moved parallel to the lines of force? 50 P a g e

51 Lenz's Law (You can't get something for nothing) Consider the diagram. Look at the magnetic field that the induced current produces. How does it interact with the external magnetic field? On the side of the conductor from you, the circular field and the permanent field are in the And on the side to you the fields are in the and thus somewhat. Where does the wire want to move? What does this do to the force required to pull the wire through the field? 51 P a g e

52 Heinrich Lenz put it this way: The electrons of an current flow in such a direction that the they create the action of the. This is known as This is all very good because the is satisfied. That is, in order to get out, you must put in. The can be supplied by as in Bay d'espoir and Churchill Falls,or by as in Holyrood. Another source of the mechanical energy that seems to be more and more desirable is. Determine the missing information 52 P a g e

53 Page 673 # 1, 2 Page # 1 4, 6, 16, 17, P a g e

54 Consider the arrangement below: If a current in one coil is inducing an emf ( ) and in another coil then: (i) the induced effects in the second coil only occur at the instant of and of the switch in the circuit of the first coil. It is only then that there is relative motion due to the and magnetic field around the first coil. (ii) the of the induced current in the second coil will depend on whether or not the switch in the first coil is or. This is because as the switch, the magnetic field around the first coil is ", and as the switch the magnetic field around the first coil is ", i.e., these two fields move in directions. In any case, the direction of the induced current will cause a magnetic field that the magnetic field in the first coil. 54 P a g e

55 Show how the two compasses and the galvanometer will point when : A) The switch closes B) The switch is opens 55 P a g e

56 Generators Describe the construction and operation of an AC/DC electric generator Sketch the characteristic graph of the current. (16.3) Generators A is any device which energy of motion into energy. They were originally called. Every generator has the following components: 1. field - either or 2. in motion - 3. to move the conductor - examples are: wind - falling water - expanding steam - gas engine - 56 P a g e

57 Operation of a simplified AC generator (page 674) slip rings contact brushes There MUST be From the induced must produce a force ( ) that opposes the motion of the. Describe how the generator works. On the right side, the external force is acting, so the induced current must exert a force. Thus the induced current is heading on the right. The opposite occurs on the left side, the external force is acting so the induced current must exert a force Thus the induced current is heading on the right. Where is the maximum induced voltage (current) produced? Where is induced voltage (current) zero? What happens when the coil reverses position from right to left?. 57 P a g e

58 The graph below shows induced current vs. rotation of the coil. This current alternates from (direction) to (direction). What is it know as? o For household AC current we have (or ) This means for every there are complete waves of electricity. What is the frequency of the electricity in Europe? For 60 Hz, what is the period of one cycle? 58 P a g e

59 The following is a sketch a graph of voltage vs. time for the AC electricity available for common household lighting and equipment. What is the amplitude of this graph? This is the graph of current vs. time for a light bulb of connected to a household AC supply. What is the power rating of the bulb? 59 P a g e

60 Sketch a graph of current vs. time for a 60 W light bulb of connected to a household AC (120 V) supply. Slightly Less Simplified AC generator 60 P a g e

61 DC Generator An AC generator can be changed into a DC generator by using a, instead of slip rings. By using the current from each brush leaves the generator in the during the complete cycle. What type of current always flows in the same direction? The graph of current vs. rotation of the coil look like this: 61 P a g e

62 NOTE: This DC electricity has a serious disadvantage over a battery because batteries deliver a current The DC generator above drops its current to every half cycle. This would not be good for any device, such as a computer, which expects a constant current. The ripple effect can be reduced by: using several, with each coil having its own pair of split rings. using a. A behaves like an electrical sponge. If a sponge is drier than its surroundings it up water. If it is wetter than its surroundings the water out of the sponge. Similarly with a capacitor: o If the capacitor contains less voltage than the circuit it " or electric charge. o The capacitor is a. o When the circuit's voltage drops lower than what is stored in the capacitor, the capacitor " some of its charge. o The capacitor becomes a. 62 P a g e

63 Schematic of circuit with DC generator and a capacitor and the graph of the resulting voltage Transformers Transformers are a necessary component of the. The principle behind the operation of a transformer comes from a simple device made by called Faraday's Ring Apparatus: (page 670) 63 P a g e

64 Magent ic Fiel d in Ring Secondar y Coil Note: There is connection between the two circuits. When the switch is closed the entire ring becomes and a current is induced in the secondary circuit. This is the same as inserting a into a coil of wire. When the switch is, the entire ring becomes and once again there is a induced current in the secondary circuit but in the. The following graphs represent the action of Faraday's Ring Apparatus. Pr imar y Coil 64 P a g e Sw it ch Cl oses Sw it ch Opens

65 (These graphs ignore the phase lags associated with induced currents and magnetic fields) Note: The secondary current only occurs as the magnetic field. As the change in the magnetic field gets the induced current gets. When the change in magnetic field so does the direction of the. The induced current in direction. Important: The problem with DC is that the switch must be to get a secondary. However if AC is used, the electricity is always being so that there will be produced in the secondary circuit. The following graphs illustrate what happens with Faraday's Ring connected to 65 P a g e

66 Primary Coil Magentic Field in Ring Secondary Coil NOTE: The induced current is in the same as the inducing current. Thus to get a (Faraday s Ring) to produce in the secondary circuit the circuit be connected to 66 P a g e