2What are magnets?Let’s first start off with what causes an magnetic field…A magnetic field is created around any moving charged object.
3What is charged that is moving within an atom? Electrons (e-)The atoms within most materials have paired up electrons spinning in opposite directions so the magnetic field that is created by one is cancelled out by the other.
4Some materials like iron, nickel, and colbalt have a single electron or pair of electrons that spin in the same direction creating a magnetic field or a small atomic magnet.
5The atomic sized magnets line up to create domains within the material. The individual domains line up to form a magnet.
6A magnet has two ends called poles (dipoles), where the magnetic force is the strongest. No matter how many times a magnet is broken, each piece always has a north pole and a south pole.There is no such thing as a monopole.
7A magnetic field exists around a magnet or any moving charged object. Magnetic fields are like electric fields or gravitational fields in that they allow magnets to interact without touching.
8Imaginary lines that map out the magnetic field (B) around a magnet are known as magnetic field lines or magnetic flux lines.
9Rules for drawing magnetic field lines (same as an electric field): 1. Magnetic field lines always go from the north pole to the south pole (outside a magnet).
10The direction of the magnetic field is determined by using a compass The direction of the magnetic field is determined by using a compass. The needle of the compass points in the direction of the magnetic field.
11Rules for drawing magnetic field lines: 2. Magnetic field lines are closed loops and never cross or intersect.
12Rules for drawing magnetic field lines: 3. Where the magnetic field lines are closer the magnetic field is stronger.
13Draw magnetic flux lines around the magnets below:
14Magnetic Field Strength (B) B = FqvThe number of magnetic lines of flux per unit areapassing through a plane perpendicular to the directionof the lines is called the magnetic field strength (B).The magnetic field strength is a vector like electric field strength.The weber (Wb) is the unit used formeasuring the number of lines of flux.1 Wb = 1 Tesla (T)m2Tesla’s are used as the unit for magnetic field strength (magnetic flux density).
15Feeling the strongest magnetic force… An object that enters this magnetic fieldwill feel a maximum forceonly if it is movingperpendicular to the flux lines.F = 0FmaxIt will feel no magnetic forceif is is movingin line, or parallel, with the flux lines.B
16MagnetismMagnetism is the force of attraction or repulsion between magnetic poles.
18What we do know… The north magnetic pole and the geographic North Pole do not coincide. The magnetic pole is about 1500 km(930 mi) south of the geographic North Pole and it wanders.A compass actually indicates the direction of magnetic north,not true north. Therefore a navigator must need to know themagnetic declination for a specific area. This is the angulardifference between magnetic and true north.The details and mechanisms ofhow and why the Earth has amagnetic field are unclear.They do believe that it mayhave something to do withmotions in the liquid outer core.
19Charges moving through a wire: Remember what createsmagnetic fields-a charged object in motion.Current is the flow of electrons. A moving charged object.Current in a wire produces a magnetic field around the wire.A compass can be used to detect amagnetic field around a wire thathad current flowing through it.
20e- LEFT HAND RULE: Helps us to analyze the path of a charged object in a magnetic field.Which way will the magnetic field below push this electron traveling through the field?NBSe-Thumb is aligned with thedirection of current (I) or movement.We use the LHR for electron flow.Fingers are alignedwith the direction ofthe magnetic field (B).Your palm indicatesthe direction theobject would movedo to the magnetic force.
21LHR Symbols: WIRE: FIELD: Sometimes the magnetic field or current is going into or out of the page.For this we us the following symbols:Coming out of pageGoing into pageWIRE:FIELD:
23Looking at wires straight on… Which way is the magnetic field around the wire? Use the LHR.
24Effects of two wires: WIRES WILL ATTRACT EACH OTHER 1. Two wires next to each other that both have currents in the same direction.WIRES WILL ATTRACT EACH OTHER
25Effects of two wires: WIRES WILL REPEL EACH OTHER 2. Two wires next to each other that have currents in opposite directions.WIRES WILL REPEL EACH OTHER
26Effects of two wires: NO INTERACTION, F=0 3. Two wires with currents flowing perpendicular to each other.NO INTERACTION, F=0
27Practice…The diagram below shows an end view of a current carrying wirebetween the poles of a magnet. The wire is perpendicular to themagnetic field.FIf the direction of the electron flow is into the page, what is thedirection of the magnetic force (F) acting on the wire?
28Practice…The wire below is moved toward the right through a magnetic field.In which direction will the magnetic force push the wire?
29Looped wire + - What’s the magnetic field around a loop of wire? Where’s thenorth polecreated?The north poleis located whereyour finger tipsend up.e-Behind the wire.+-
30+ - What’s the magnetic field around a loop of wire? Where’s the north polecreated?+-e-Above the wire.Looping a wire around several times into a coil will produce an…
31…Electromagnet An electromagnet is a type of magnet whose magnetic field is produced by the flow of electriccurrent. The magnetic field disappears when thecurrent ceases.
32adds to the field of any others moving in the same direction. An electromagnet is most commonly made by coiling wire around a piece of iron. This electromagnet is called a solenoid. The shape of the magnetic field is the same as a bar magnet.As electrons move through the coil of wire, the magnetic field of one electronadds to the field of any others moving in the same direction.
33Factors affecting the magnetic field of a solenoid: The magnetic field around a solenoid is directlyrelated to the current through the coil.
34Factors affecting the magnetic field of a solenoid: 2. The magnetic field around a solenoid is directlyrelated to the number of turns or coils aroundthe solenoid.
35Factors affecting the magnetic field of a solenoid: 3. The magnetic field around a solenoid is directlyrelated to the material around which the wire iscoiled. The soft iron is more permeable to themagnetic field than the air is.
36Determining the poles of a solenoid: LHR Modified:Have palm away from you.Point fingers of left hand inthe direction of the current(many coils, many fingers).3. Stick thumb out and that’swhere the north pole is.
38Electromagnetic Induction This is the process of generating a potential difference(voltage) in a conductor (wire) due to the motionof the conductor in a magnetic field.Generating a voltage in a wire would mean generatingareas of uneven charge within a wire.How can this be done?What can be forced to move within a wire that will create a potential difference?Moving a wire through a magnetic field will cause a magnetic forcewhich will move electrons towards one end of the wirecreating a potential difference.
39Let’s take a closer look… Motion of wireB-----wire-If this wire is moved up or down (perpendicular to the field), a voltagewill be generated and if the wire is part of a completecircuit then current is induced.If this wire is moved left or right (parallel to the field),no current will be generated because no force is generated tomove electrons and create a voltage.
41This is how Niagara Falls was used to produce electricity… Water flow is used to turn aturbine through a magnetic fieldinducing a potential difference andproducing electrical current.
42This is how an electric motor works… An electric motor utilizes theproperty of electromagneticinduction to convert electricityinto mechanical energy to makethings move. The conductor itself,a coiled wire, will move to opposethe magnetic field. Just when itgets into position the current isreversed, and the coil spins roundand round and round full ofmechanical energy.
43A Generator… A generator is simply the same process in reverse, convertingmechanical energy into electricity.Almost all of the electrical energywe use in our daily lives issupplied by electric generators.
44Combo-Circuits Quiz RT= 6 Ω IT= 5 A VT= 30 V I1= 5 A PART 1: Combination Circuits- Find the following. Make sure to show work!R1 = 2 ΩR2 = 6 ΩR3 = 12 Ω30 V0 VRT= 6 Ω IT= 5 AVT= 30 V I1= 5 AV1= 10 V I2= 3.33 AV2= 20 V I3= 1.66 AV3= 20 V
45PART 2: Magnetic Fields- For each diagram representing a magnet or current-carrying conductor below, draw in the associated magnetic field lines.If the lines are in the plane of the paper, represent them with arrows in theappropriate direction. If the field lines are coming out of the plane of thepaper, represent them with DOTS ; if they are going into the paper, representthem with CROSSES .3.1.current carrying wireperpendicular to the page2.4.
46and a CROSS means the direction is out of the page towards you. PART 3: Magnetic Force Direction- The following diagrams show a chargedparticle or a current carrying wire in a magnetic field. For each diagram usethe left-hand rule to draw an arrow on the object that shows the direction ofthe magnetic force. Remember that a DOT means the direction is into the pageand a CROSS means the direction is out of the page towards you.Bv into paperB3.1.BI-B out of paper2.4.