Introduction to electromagnetism

1. PHYSICS
INTRODUCTION TO
ELECTROMAGNETISM
TEACHER: Telman Askeraliyev, MSc, Italy

2. OBJECTIVES
•Describe Hans Christian Ørsted’s discovery about current-carrying wires.
•Investigate and describe the relationship between electric current and
magnetic fields in wires and solenoids.
•Describe how electromagnets are used in many applications.

3. MISSING LINK
Before 1820, scientists suspected that electricity and magnetism were related,
but they had no proof.
Can you think of any similarities between electricity and magnetism that made
scientists suspect a link?

4. DISCOVERY

5. CURRENTS CREATE MAGNETISM
Current-carrying wires create magnetic fields.
But what do these fields look like?
They circle around the wires!

6. CURRENT AND MAGNETIC FIELD

7. CURRENTS CREATE MAGNETISM
The magnetic field circles
around the current-carrying
wire, and points tangent to
the circle.

8. DIRECTION OF MAGNETIC FIELDS
Use the right-hand rule to find the
direction of the magnetic field.
• Point the thumb of your
right hand in the direction
of the current.
• Fingers curling around the
wire point in the direction
of the magnetic field.

9. DIRECTION OF MAGNETIC FIELDS

10. ELECTROMAGNETS

11. THE SOLENOID
The magnetic field around a single wire may
not be very strong.
A solenoid uses many loops of current-
carrying wire to create a stronger magnetic
field.

12. ELECTROMAGNETS
Electromagnets are made by wrapping a
coil of wire around a iron core.
The iron core makes the magnet even
stronger.

13. APPLICATIONS OF ELECTROMAGNETS
Electromagnets have many useful
applications, such as:
The strength and polarity of
electromagnets can be controlled by
the adjusting the amount and direction
of current and number of loops.
• motors
• computer hard drives

14. MAGNETIC FIELD

15. THE MAGNETIC FIELD
A magnetic field is said to exist at a point if a compass needle
placed there experiences a force.

16. MAGNETIC FIELD PATTERNS
A bar magnet is a piece of ferrous metal which has a north and a
south pole. Looking at the B-field about such a magnet, determine
the north and the south poles.
By convention, the direction of the magnetic field lines is the
direction a north-seeking pole would point if placed within the field

17. MAGNETIC FIELD PATTERNS

18. MAGNETIC FIELD PATTERNS

19. MAGNETIC FIELD PATTERNS
Magnetic Field Lines –
- Arrows give
direction – Density
gives strength
– Looks like dipole!

20. MAGNETIC FLUX
The magnetic flux is a measure of the
number of field lines passing through a
region.
The unit of magnetic flux is the weber (Wb)
It is a vector quantity

21. MAGNETIC FLUX
In a uniform field
the number of
field lines passing
through the larger
region B is greater
than through the
smaller region A.
Therefore we can
say that there is a
greater flux
through B than A
A
B

22. MAGNETIC FLUX
magnetic flux () – a measure of the number
of field lines passing through and area (A). The variable we use to
represent magnetic flux is capital phi.
a) The area can be represented by a vector A perpendicular
to the plane of the area.
b) When the plane of a rotating loop is perpendicular to the
field and  = 0°, then  = max = BA.
c) When  = 180°, the magnetic flux has the same magnitude
but is opposite in direction:  = - max = - BA.
d) When and  = 90°, then  = 0.

23. MAGNETIC FLUX

24. MAGNETIC FLUX

25. MAGNETIC FLUX
m = BA cos  magnetic flux
where B is the magnetic field
A is the area of the loop
 is the angle between B and A
• The unit of magnetic flux is the weber (Wb). 1 Wb = 1 T·m2

26. MAGNETIC FLUX
• If the coil has N number of turns, then the total flux through the
coil is the sum of the flux through each turn. Hence,
m = NBA cos  magnetic flux through a solenoid

27. QUIZ 1
But which way does it circle?
Here are two possibilities:
direction of
electric current
direction of
magnetic field??
The magnetic field circles
around the current-carrying
wire, and points tangent to
the circle.

28. QUIZ - ASNWER
direction of
electric current
direction of
magnetic field

29. THANK YOU!