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5.14 MAGNETIC FIELDS AND ELECTRIC CURRENT

Explore how magnetic fields are generated by electric currents and the application of electromagnetism with detailed explanations of solenoids, cores, and hand rules.

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5.14 MAGNETIC FIELDS AND ELECTRIC CURRENT

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  1. Write this title into your notebook. 5.14 MAGNETIC FIELDS AND ELECTRIC CURRENT

  2. Write this in your notebook. • A magnetic field is created whenever an electric current flows through a conductor. • This is electromagnetism. • The conductor can be a: • “straight-line conductor” (uncoiled wire) or • coiled wire (a.k.a solenoid)

  3. A Solenoid: Write this in your notebook. • When a current flows through the wire …. a magnetic field is generated • Similar to that of a bar magnet. • Is a wire wrapped around a core. Electromagnet

  4. Cores: Write this in your notebook. • A Core is the object that is inserted into the solenoid, creating an electromagnet. • easy to align or misalign the domains • Different ferromagnetic metals can be used for the core: iron, nickel or cobalt. • Iron is most commonly used because when you turn off the electricity it demagnetizes! • Steel is usually not used because it is difficult to demagnetize.

  5. The “Hand” Rules • There are two sets of “hand” rules that can be used to determine the direction of the magnetic field around an electrical conductor • Your choice of which set of rules to use depends on which system you use to describe electric current: • Electron Flow or Conventional Current • Both systems are correct, and both work, but you must be careful not to mix them up! • The “Left Hand Rules” are covered in slides 6 to 11 • The “Right Hand Rules” are covered in slides 12 to 17

  6. Left Hand Rule

  7. 5.15 The Left Hand Rules Write this in your notebook. • This rule will help you determine the direction of the magnetic fields created by an electric current. • The 1st Left Hand Rule is used with a straight wire (uncoiled). • The 2nd Left Hand Rule is used with a solenoid (or coil) • Remember electrons flow from – to + !!!!

  8. Straight Line Conductors (Uncoiled) Write this in your notebook. + • Find the + and - ends of the wire • Point your thumb in the direction of the electron flow (towards +end) • Your fingers are pointing in the direction of the field Direction of the electron flow -

  9. Electron flow (left hand rule) Conventional current (right hand rule)

  10. Solenoids (or coils) Write this in your notebook. • Find the +and - ends of the wire • Draw arrows on the front of the coil pointing in the direction of the electron flow (towards +). • Place your hand on the page with your fingers pointing in the direction of the electron flow. • Your thumb will point towards the north end of the solenoid. Up behind the core and Down in front of the core. N S - +

  11. The Left Hand Rules will help you with all of the electromagnetic problems …got it? Jump to slide 18

  12. The Right Hand Rules

  13. Conventional Current • If you use “conventional current” to describe the direction of the current, it is said to flow from the positiveto the negative terminal • You must use the “Right Hand Rules”

  14. There are two “hand rules” that will help you to determine the direction of the magnetic fields created by electric currents. • The 1st Right Hand Rule is used with a straight line or uncoiled wire. • The 2nd Right Hand Rule is used with a solenoid (or coil)

  15. Straight Line Conductors (Uncoiled Conductors) - • Find the positive and negative ends of the wire • The conventional current flows from positive to negative • Point thumb of your right hand in the direction of the conventional current • Wrap your fingers around the wire • Your fingers will point in the direction of the magnetic field Direction of the magnetic field Direction of the Conventional Current +

  16. Solenoids (or coils) Up behind the core and Down in front of the core. • Find the positive and negative ends of the wire • The conventional current flows from positive to negative • Draw (or imagine) arrows on the front of the coil pointing in the direction of the conventional current. • Wrap your right hand around the solenoid with your fingers pointing in the direction of the electron flow (in the direction of the arrows). • Your thumb will point towards the north end of the solenoid. S N - +

  17. The Right Hand Rules will help you with all of the electromagnetic problems …got it?

  18. Solenoid Example - # 1 • Find the positive and negative ends of the wire • Determine the direction of the electric current • Wrap your fingers around the coil pointing in the same direction as the current • Thumb points “N”. Other end is “S”. • Lines of Magnetic force run Nto S . N S - +

  19. Solenoid Example # 2 • Find the positive and negative ends of the wire • Determine the direction of the electric current • Wrap your fingers around the coil pointing in the same direction as the current • Thumb points “N”. Other end is “S” • Lines of Magnetic force run Nto S S N - +

  20. Determining the Direction of the Magnetic Field around a Straight Line Conductor + - + - + + - -

  21. Effects of a Straight Line Conductor on a Compass Determine the direction of the Magnetic Field - + Compass Compass arrow Points in the same direction as the Magnetic Filed

  22. The Continuous Magnetic Field Around a Straight-line Conductor + - • If we reverse the terminals, the magnetic field will flow in the opposite direction • And the magnets will point the other way… • The magnetic field flows in a continuous circle around the wire perpendicular to it. • Determine the direction of the magnetic field • Compasses placed around the wire will point in the direction of the magnetic field - +

  23. Determine the direction that the compass would point if it were placed on top of the wires as illustrated. Straight Line ConductorExamples + B A + - + - + D C - -

  24. Write this in your notebook. 5.15 continued • Hand Rule for Straight Line Conductors: • Your thumb points in the direction of the electric current • Yourfingers will point in the direction of the magnetic field • There is no North or South Pole. • The magnetic field flows in a continuous circle around the wire. • The compass points in same direction as the magnetic field.

  25. Write this in your notebook. 5.16 Electromagnetic Induction • Is the process where you use a moving magnetic field to produce an electrical current. (p171)

  26. Write this in your notebook. • This is achieved by: • Moving a conductor perpendicularly inside the magnetic field • Moving a magnet around a conductor • eg. Hydro electricity • Electric generators

  27. How it works.

  28. Finish for homework if needed • Textbook p174 21 to 25

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