MAGNETIC FIELDS AND ELECTRIC CURRENT

1. MAGNETIC FIELDS AND ELECTRIC CURRENT Electromagnetism: when an electric current flows through a wire a magnetic field is created.

2. Conductors • A magnetic field is created whenever an electric current flows through a conductor • The conductor can be a “straight-line” conductor (i.e. an uncoiled wire) • Or it can be a coiled wire called a solenoid or a coil

3. Solenoid • Wire wrapped around a core (tube) • Have a current flowing through them • Have a magnetic field • Their magnetic fields look like the magnetic field around a bar magnet. Electromagnet

4. Cores • A Core is the object that is inserted into the solenoid, creating an electromagnet. • Different materials influence the strength of the electromagnet. • Different metals can be used for the core: iron, steel, nickel or cobalt. • Iron is most commonly used because when you turn off the electricity it demagnetizes. • Metals like steel remain magnetized thus creating a permanent magnet.

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. The Left Hand Rules

7. Electron Flow • If you use “electron flow” to describe the direction of the current, it flows from the negative to the positive terminal • You must use the “Left Hand Rules”

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

9. Straight Line Conductors (Uncoiled Conductors) + • Find the positive and negative ends of the wire • The electrons flow from negative to positive • Point the thumb of your left hand to + with hand flat on page • Your knuckles will be on the NORTH • Your fingertips will be on the SOUTH Direction of the electron flow -

10. Solenoids (or coils) • Find the positive and negative ends of the wire • The electrons flows from negative to positive • Draw (or imagine) arrows on the front of the coil pointing in the direction of the electron flow. • Place your hand on the page 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. 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?

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 (Nerd to Sexy). 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 (Nerd to Sexy). N S + -

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. Key Points to Remember • 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 • North and South are never on the ends of the wire • There is no North or South Pole. The magnetic field flows in a continuous circle around the wire. • The magnetic field flows in the same direction as the compass points.