Electromagnetism introduction in the radiology world

1. ELECTROMAGNETISM

2. ELECTROMAGNETIC
FORCE
•Electricity and magnetism are
different aspects of same
electromagnetic forces
•Electromagnetic force is one of
the fundamental forces of nature
•The development of the battery
led to an increased understanding
of Electromagnetic phenomena

3. BATTERY
•discovered by Italian anatomist,
Alessandro Volta, 1700s
•Using zinc and copper plates, he
succeeded in producing a feeble
electric current. To increase the
current, he stacked the copper-zinc
plates similar to a Dagwood sandwich to
form what was called the Voltaic pile, a
precursor of the modern battery.

4. BATTERY
•Each zinc-copper sandwich is
called a cell of a battery
•Modern dry cells use a carbon
rod as the positive electrode
surrounded by an electrolytic
paste housed in a negative zinc
cylindrical can.

5. BATTERY
•The battery is an example of
Electromotive Force (EMF)
•Any device that converts some
form of energy into electric energy
is said to be a source of EMF or
stored electric energy
•EMF has units of joules per
coulomb or volts

6. ELECTRICITY AND
MAGNETISM
1820- Hans Oersted, Danish physicist,
fashioned a long, straight wire supported
near a free-rotating magnetic compass.
With no current flowing through the wire,
the magnetic compass pointed north as
one would expect.
When a current was passed through the
wire, however, the compass needle swung
to point straight at the wire.

7. ELECTRICITY AND
MAGNETISM

8. •Oersted’s experiment
demonstrated that electricity can
be used to generate magnetic
fields.
•This was evidence of a direct link
between electric and magnetic
phenomena.

9. •Any charge in motion induces
a magnetic field.
•A charge at rest produces no
magnetic field. Thus electrons
flowing through a wire produce a
magnetic field around the wire

10. •The direction of the magnetic field
lines can be determined by using what is
called RIGHT-HAND RULE.
•Imagine gripping the wire with the
right hand. If the thumb is pointed in
the direction of the current flow, the
fingers of your hand will then curl in
the direction of the magnetic lines.
These same rules apply if the current is
flowing in a circular loop.

11. Right hand rule:

12. •A coil of wire is called a SOLENOID
•An ELECTROMAGNET is a ferromagnetic
materials wrapped in a coil of wire.
•The magnetic field produced by an
electromagnet is the same as that produced by
a bar magnet.
•The advantage of the electromagnet is that its
magnetic field can be adjusted or turned on and
off simply by varying the current flow through
its coil of wire

13. LAWS OF ELECTROMAGNETIC
INDUCTION
First law: FARADAY’S LAW
Michael Faraday’s law says
that an electric current will be
induced to flow in a circuit if
some part of that circuit is in
a changing magnetic field.

14. LAWS OF ELECTROMAGNETIC
INDUCTION
First law: FARADAY’S LAW

15. LAWS OF ELECTROMAGNETIC
INDUCTION
First law: FARADAY’S LAW
Faraday’s concluded that an electric
current cannot be induced in a
circuit merely by the presence of a
magnetic field. To induce a flow of
current using a magnetic field, the
magnetic field cannot be constant
but must be changing.

16. LAWS OF ELECTROMAGNETIC
INDUCTION
Second law: LENZ’ LAW
1834, a Russian scientist,
Heinrich Lenz expanded on
Faraday’s work. He established
the principle for determining
the direction induced current
flow.

17. LAWS OF ELECTROMAGNETIC
INDUCTION
Second law: LENZ’ LAW
Heinrich Lenz’ law states that induced
current flows in a direction such that it
opposes the action that induces it.

18. There are 2 basic types of induction
(production of electricity in the
magnetic field):
1. Self- induction
The induction of an opposing
EMF in a single coil by its
own changing magnetic field.

19. There are 2 basic types of induction
(production of electricity in the
magnetic field):
1. Self- induction

20. There are 2 basic types of induction
(production of electricity in the
magnetic field):
2. Mutual-induction
•The process of inducing a
current flow through a
secondary coil passing a
varying current through the
primary coil.

21. There are 2 basic types of induction
(production of electricity in the
magnetic field):
2. Mutual-induction

22. ELECTROMECHANICAL AND
ELECTRONIC DEVICES
1. Electric generator
2. Electric motor
3. Transformer
4. Rectifier

23. ELECTROMECHANICAL AND
ELECTRONIC DEVICES
1. Electric generator
In a electric generator a coil of wire
is placed in a strong magnetic field
between two poles of a magnet
Converts mechanical to electrical
energy

24. ELECTROMECHANICAL AND
ELECTRONIC DEVICES
2. Electric motor
•In an electric motor the electric
energy is supplied to the current loop to
produce a mechanical motion, that is
the rotation of the loop in the magnetic
field
•Converts electrical to mechanical
energy

25. ELECTROMECHANICAL AND
ELECTRONIC DEVICES
3. Transformer
•Electric potential and electric and
electric current are changed to higher
or lower intensities.
•Transformer operates on the principle
of mutual induction, it will only operates
with a changing electric current (AC)

26. Transformer Law for Voltage:
VS = NS
VP VP

27. Transformer Law for Current:
IS = NP
IP IS

28. Transformer Law for Voltage
and Current:
IS = VP
IP VS

29. There are 125 turns on the primary side
of a transformer and 90, 000 turns on
the secondary side. If 110V AC is
supplied to the primary winding, what will
be the voltage induced in the secondary
winding?
125X = 9,900,000 X= 79, 200V
125 125 or X= 79.2 kV

30. The turns ratio of a filament transformer
is 0.125. what will be the filament current
if the current flowing through the
primary winding is 0.8 A?
0.125X = 0.8_
0.125 0.125
X= 6.4 A

31. Types of transformers:
1. Closed-Core Transformer
•The closed core transformer is a square
doughnut of magnetic material
•The closed-core transformer is not a single
piece but rather is a built-up slab of laminated
layers of iron.
•This layering helps reduce energy losses
caused by the heat built up by the changing
magnetic field in the transformer.

32. Types of transformers:
1. Closed-Core Transformer

33. Types of transformers:
2. Autotransformer
•An autotransformer consists of an iron core
with only one winding of wire.
•This single winding acts as both the primary
and the secondary winding.
•The transformer is based on the self
induction rather than the mutual induction.
•The autotransformer is not suitable for the
use as the high-voltage transformer in an x-
ray machine

34. Types of transformers:
2. Autotransformer

35. Types of transformers:
3. Shell-type transformer
•A shell-type transformer traps even
more of the magnetic field of the
primary winding and is thus a more
efficient transformer than closed-core
transformer.
•This type of transformer used in modern
x-ray equipment.

36. Types of transformers:
3. Shell-type transformer

37. ELECTROMECHANICAL AND
ELECTRONIC DEVICES
4. Rectifier
•Changes AC to DC
•Types of rectifiers:
1. Vacuum-Tube rectifiers
Ex: X-ray tube (cathode &
anode)
2. Solid-state Rectifiers
N-type
P- type

38. END