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 and wrap your hand around the conductor.
The direction of your fingers curved around the conductor will determine the magnetic flow. Knuckles = N and Fingertips = S
Direction of the
electron flow -

11. - Solenoids (or coils) + N S
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 - +

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

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

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

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

18. 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

19. 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 - +

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

21. Key Points to Remember
Hand Rule for Straight Line Conductors – Your thumb points in the direction of the electric current
Your fingers 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.