1. Applications of Inductor
Section 6.4

2. Magnetic Field
Applications of Electromagnetism
Transformer

3. Magnetic Field Flux lines are used to represent the strength
and the direction of the field.
The flux lines are always drawn from the north pole to the south pole.

4. Flux Lines of magnets
Unlike Poles Attract
Like Poles Repel

5. How materials become magnetized
Ferromagnetic Materials such as iron and nickel become magnetized when
Placed in the magnetic field of a magnet
Objects become magnetized (i.e. they become magnets themselves) under the
Influence of the permanent magnetic field and become attracted to the magnet.
When removed from the magnetic field, the objects tends to lose its magnetism.
Ferromagnetic materials have minute magnetic domains created within their
atomic structure.

6. Application 1: Magnetic switch
When the magnet is near the switch mechanism, the switch is closed.
When the magnet is moved away, the spring pulls the arm open.

7. Electromagnetism

8. Magnetic Field
Note: The field is stronger closer to the conductor and becomes weaker
with increasing distance from the conductor.

9. Right-Hand Rule Thumb: Points in the direction of current
Fingers: point in the direction of the magnetic lines of force.

10. Cumulative magnetic force

11. Application #1: Electromagnet
When the coil of wire is connected to a battery, there is current.
A magnetic field is established.

12. Application #2

13. Solenoid A basic solenoid consists of three parts: (Section 10-3)
1. Coil
2. A stationary iron core
A sliding core (plunger) is attached to the stationary core with a spring.
Applications: opening and closing valves and automobile door locks.

14. In the rest state, the plunger is extended.
Magnetic fields in the core points from right to left.
Steps:
In the rest state, the plunger is extended.
The solenoid is energized by current through the coil, which sets up an
electromagnetic field that magnetizes both iron cores.
3. The south pole of the stationary core attracts the north pole of the movable
coil causing it to slide inward, thus retracting the plunger and compressing the spring.
When the current is cut off, the magnetic fields collapse and the force of the
Compressed spring pushes the plunger back out.

15. Application #3
A relay is used to open or close electrical contacts.

16. When there is no coil current, the iron armature is held against the upper contact
by the spring, thus providing continuity from terminal 1 to terminal 2.
When energized with coil current, the armature is pulled down by the attractive
force of the electromagnetic field and makes connection with the lower contact,
providing continuity from terminal 1 to terminal 3.

17. Application #4 Reed Relay
Reed is made of ferrous material.
When there is no coil current, the reeds are in the open position.
Where there is current, the reeds make contact because they are magnetized
and attract each other.

18. Application #5: Meter Movement

19. Current in: crowded flux lines above, resulting in downward force on the right.
Current out: crowded flux lines below, resulting in upward force on the left.

20. A transformer

21. Polarity of transformerB B I
Bind
Bind I I

22. Symbols of transformer

23. Dot Convention (Section 6.4)
When the reference direction for a current enters the dotted terminal of a coil,
the reference polarity of the voltage that it induces in the other coil is positive
at its dotted terminal.

24. How to use Dot Convention in Circuit Analysis
i2 leaves the dotted terminal.
i2 leaves the dotted terminal, therefore, the induced voltage across L1 is
negative.
i1 enters the dotted terminal, therefore, the induced voltage across L2 is
positive.

25. A Procedure for Determine Dot Markings

26. Example

28. Practice for Determining Dot Markings

29. Alternate Technique for Determining Polarity Marks

30. We will revisit transformer in Chapter 9.

31. Example 6.6

32. Derivation of L1 and M

33. Derivation of L2 and M

34. Energy Storage