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Chapter 21: Magnetism

Chapter 21: Magnetism. What is a magnet? A magnet is anything that carries a static magnetic field around with it.. A magnet has a North and South pole. Magnetic lines of flux make up the magnetic field and travel from North to South outside of the magnet.

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Chapter 21: Magnetism

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  1. Chapter 21: Magnetism

  2. What is a magnet? • A magnet is anything that carries a static magnetic field around with it.. • A magnet has a North and South pole. • Magnetic lines of flux make up the magnetic field and travel from North to South outside of the magnet. • This magnetic field is responsible for the force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.

  3. Chapter 21 Describe a permanent magnet. • Permanent Magnets are the most common type of magnets . These magnets are permanent in the sense that once they have been magnetized they retain a certain degree of magnetism. • Permanent magnets are generally made of ferromagnetic material. Such material consists of atoms and molecules that each have a magnetic field and are positioned to reinforce each other.

  4. Chapter 21 The four types of permanent magnets are: 1. Neodymium Iron Boron (NdFeB or NIB) strongest types. From the rare earth or Lanthanide series of elements . 2. Samarium Cobalt (SmCo) weak and affected by temperature. 3. Alnico weak and can easily become demagnetized. Least affected by temperature. 4. Ceramic or Ferrite Most popular, strength varies greatly with Temp

  5. Chapter 21 Explain why some materials are magnetic and some are not. • It's all about unpaired electrons. • The transition metals add electrons to the second shell in, so there is the possibility of them being unpaired. Hence Fe Co and Ni. • The other Ferro magnets are the rare earths, which likewise are filling the second rather than the outer shell.

  6. Chapter 21 Draw the magnetic field of a Bar Magnet

  7. Chapter 21 How are magnets similar to charges? How are they different? (C1) • Similar in the following ways: • In charges positive (+) and negative (−) electrical charges attract each other. • In magnets, the N and S poles attract each other. • In electricity, like charges repel • In magnetism like poles repel.

  8. Chapter 21 2. Different in the following ways: • The magnetic field must have two poles (N and S). • A positive (+) or negative (−) electrical charge can stand alone. How can you determine the polarity of a magnet? (C2) • Polarity identifies a magnets North and South Pole. • The North Pole is attracted to the Earth’s geographic North Pole and the south pole of the magnet is attracted to the earth’s geographic South Pole.

  9. Chapter 21 3. Unknown magnet Polarity : a. Suspend the magnet by a thread. b. The North Pole of the magnet will point towards the geographic North Pole. c. A known polarity magnet brought near the suspended magnet will attract the opposite pole and repel the like pole. - Like poles repel (N-N, S-S) - Unlike poles attract (N-S, S-N)

  10. Chapter 21 Determine the polarity of the Earth and compare the poles to the geographical poles. WARNING WARNING WARNING • The geographic north pole is the magnetic south pole. • The geographic south pole is the magnetic north pole.

  11. Chapter 21 What are magnetic domains? What does the magnetic domain depend on? (C3) • Magnetic substances like iron, cobalt, and nickel are composed of small areas where the groups of atoms are aligned like the poles of a magnet. These regions are called domains. • All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field. • The magnetic domain depends on the type of material. Ferromagnetic materials form large magnetic domains.

  12. Chapter 21 The Domain Theory States that the atoms have their magnetic field lines line up forming atomic magnets called dipoles. The alignment of groups of atomic magnets (dipoles) form domains. It is these aligned domains that then form a bar magnet.

  13. Chapter 21

  14. Chapter 21 What is the magnetic field?(C4) • A magnetic field consists of imaginary lines of flux coming from moving electrically charged particles. (Ex. Electric current) • A charge moving through this magnetic field experiences a force. Calculated by F= Bqv • The SI unit for magnetic field (B) is the Tesla (T). 1T=N/(Cm/s).

  15. Chapter 21 4. Magnitude of a magnetic field (B) is calculated using: B = Fmagnetic /qv • Fmagnetic = magnetic force on a charged particle (N) • q = magnitude of charge (c) • v = speed of charge (m/s)

  16. Chapter 21 Draw the Earth’s Magnetic Field

  17. Magnetic Field of a current carrying conductor.(Right Hand Rule)

  18. Chapter 21 How can magnetic field lines be used to find the poles of a magnet? (C5) • Magnetic field lines travel from North to South Poles outside of the magnet. • A compass reveals that magnetic field lines outside of a magnet point from the north pole (compass points away from north pole) to the south (compass points toward the south pole).

  19. Chapter 21 How do we know that the Earth is a giant magnet?(C6) • The compass was used to discover that the Earth is a huge magnet. The North-seeking pole of the compass needle will always point toward the Earth's North magnetic pole.

  20. Chapter 21 Give two examples of the effect of Earth’s magnetic field. • Deflects the needle of a compass. • Interferes with AM radio • Northern lights

  21. Chapter 21 How is the Right Hand Rule used to figure out the direction of force, field, and current? (C7) • Hold your right hand as if you were going to shake someone's hand. The thumb forms a right angle with the index finger. Thumb- Direction of current flow (+ to -) Fingers- Direction of magnetic field Palm- Direction of force

  22. Right Hand Rule

  23. FLEMMINGS RIGHT HAND RULE • Also known as the Generator Rule this is a way of determining the direction of the induced emf of a conductor moving in a magnetic field. The thumb, the first and the second fingers on the right hand are held so that they are at right angles to each other. If the first finger points in the direction of the magnetic field and the thumb in the direction of the motion of the conductor then the second finger will point in the direction of the induced emf in the conductor.

  24. FLEMMINGS LEFT HAND RULE • Also known as the Motor Rule this is a way of determining the direction of a force on a current carrying conductor in a magnetic field. The thumb, the first and the second fingers on the left hand are held so that they are at right angles to each other. If the first finger points in the direction of the magnetic field and the second finger the direction of the current in the wire, then the thumb will point in the direction of the force on the conductor.

  25. Chapter 21 What is the difference between the Right Hand Rule and the Left Hand Rule? (C8) • The right hand rule is used to determine the direction of induced current when a conductor is moved through a magnetic field. • The left hand rule is used to determine the direction of the force (motion) on a current carrying conductor in a magnetic field.

  26. Chapter 21 How are the magnetic fields and electric fields related? (C9) • Electric fields result from the strength of the charge while magnetic fields result from the motion of the charge, or the current. • A changing magnetic field creates electrical current---an electric field. • The magnetic field will be perpendicular to the electric field and vice versa.

  27. Chapter 21 What conditions are necessary for a current to be induced in a wire? (10) • The wire must be a current carrying conductor connected into an electric circuit. • The wire must move through a magnetic field or the field must move through the stationary conductor. • This is called electromagnetic induction.

  28. Section 1 Electricity from Magnetism Chapter 20 Electromagnetic Induction in a Circuit Loop

  29. Chapter 21 What is an electromagnet and how is it made? (C11) • An electromagnet is a magnet that runs on electricity. a. Strength depends on the amount of electric current. b. The poles can be reversed by reversing the current flow. • One can be made by: • Wrapping insulated copper wire around an iron core. • Attach a battery to the wire. • Current will begin to flow and the iron core will become magnetized. • When the battery is disconnected, the iron core will lose its magnetism.

  30. Chapter 21 What is Lenz’s Law and how does it relate to Faraday’s Law? (C12) • Lenz’s law -The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it.

  31. 2. Lenz’s law allows you to determine the direction of an induced current in a circuit. 3. Faraday’s law- The emf (Voltage) generated through magnetic induction is proportional to the rate of change of the magnetic flux. *the (-) in front of N comes from Lenz’s law

  32. Chapter 21 What is the electromotive force (emf)? (13) • When a voltage is generated by a battery, or by the magnetic force according to Faraday's Law, this generated voltage has been traditionally called an "electromotive force" or emf. • The emf represents energy per unit charge (voltage) which has been made available by the generating mechanism and is not a "force". • Emf is voltage

  33. Chapter 21 What is an electric motor and how does it work?(C14) • Rotating coils of wire with current flow are driven by the magnetic force exerted by a magnetic field on an electric current. • Motors transform electrical energy into mechanical energy through motor action. • Motor action- When a current-carrying conductor is located in an external magnetic field the conductor experiences a force due to the interaction between the two fields.

  34. Chapter 21 How is an electric motor similar to a generator? (C15) • A generator works by the turning of a coil in a magnetic field which induces voltage (emf) in the coil. Current flows out of the coil to the circuit loads. • Generator action- A conductor, a magnetic field and relative motion between them will result in a voltage being induced in the conductor.

  35. Chapter 21 4. Reversing a generator can cause motor action. 5. Reversing a motor can cause generator action. 6. The machines can be converted to motors or generators. Such machines are called motor-generators.

  36. Chapter 21 What is mutual and self-inductance and how do they occur in circuits?(C16) • The changing magnetic field created by one circuit (the primary) can induce a changing voltage and/or current in a second circuit (the secondary). (Transformer works this way) • The mutual inductance, M, of two circuits describes the size of the voltage in the secondary induced by changes in the current of the primary:

  37. Chapter 21 3. Self Inductance- When current changes in a individual circuit the magnetic field caused by the original current flow begins to collapse. This induces an opposing voltage in the circuit.

  38. Chapter 21 What types of radiation are considered part of the electromagnetic spectrum? (C17) • Radio waves • Microwave • Infrared • Visible • Ultraviolet • X-Ray • Gamma Rays

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