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## Magnetic Forces, Fields, and Oersted

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### MAGNETIC FORCES, FIELDS, AND OERSTED S PRINCIPLE Lesson 10 A magnet is a material or object that produces a magnetic field. The distribution of a magnetic force in ... – PowerPoint PPT presentation

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Title: Magnetic Forces, Fields, and Oersted

1
Magnetic Forces, Fields, and Oersteds Principle
• Lesson 10

2
• A magnet is a material or object that produces a
magnetic field.
• The distribution of a magnetic force in the
region of a magnet.
• Magnets are labelled North and South and have the
same field laws as electric charges.
• Similar magnetic poles repel and dissimilar poles
attract.

3
• To map a magnetic field a test compass can be
used. Much like a test charge, a test compass
will point north in line with the south field.

4
• Magnetic forces can act between some metals that
are not magnetic. These metals are called
Ferromagnetic metals and include metals such as
cobalt, iron, nickel, or mixtures of the three.

5
• The atomic structure of these metals seems to
make them strongly magnetic. Think of magnetic
materials, being made up of a lot of smaller
magnets.

6
Domain Theory of Magnets
• All large magnets are made up of many smaller and
rotatable magnets, called dipoles, which can
interact with other dipoles close by. If dipoles
line up, then a small magnetic domain is
produced.

7
Electromagnets
• Force at a distance is the common element between
electrostatics and magnetism. Hans Oersted
studied this and came up with the following
principle.
• Charge moving through a conductor produces a
circular magnetic field around the conductor.

8
• Mapping the magnetic field of a conductor enables
one to be able to predict the direction of the
electromagnetic force from the current.
• There are several hand signs developed to predict
how magnetic forces will act.

9
Left-hand rule 1 for Conductors (LHR 1)
• Grasp the conductor with your left hand such that
the thumb points in the direction of the electron
(-) current flow. The curved fingers point in the
direction of the circular magnetic field around
the conductor.

10
• Using this rule allows us to produce a weak
magnet that we can turn on and off.
• To make the electromagnet stronger and straighten
out the field so that it is more like a bar
magnet, the wire conductor is made into a coil.
The individual field lines fall on top of each
other strengthening the entire field. Coiling the
wires also straightens out the field.

11
Left hand rule 2 (LHR2)
• Grasp the coiled conductor with the left hand
such that the curled fingers point in the
direction of the electron (-) current flow
through the conductor. The thumb points in the
direction of the magnetic field within the coil.
Outside the coil, the thumb represents the north
(N) end of the electromagnet produced by the
coil.

12
• This allows us to create a magnet that acts like
a bar magnet but that can be tuned off when it
needs to be. The other advantage is that strength
of the electromagnet can be controlled by the
following factors.

13
1. Current in the coil
• The greater the current flow, the greater the
field strength. Strength varies directly as the
current in the coil.

14
2. Number of turns in the coil
• The greater the number of coils, the greater the
field strength. Strength varies directly as the
number of turns in the coil of the current is
constant.

15
3. Type of material in the coils centre
• The more ferromagnetic the material within the
coil, the greater the magnets strength. Iron is
one of the better materials to use.

16
4. Size of the coil
• the smaller the diameter of the coil, the
stronger the magnetic field.

17
Questions
• Given the direction of current flow in the
conductor seen below, find the direction of the
magnetic field.
• Given the direction of the magnetic field, find
the direction of the current in the conductor
seen to the right.
• What happens to the strength of the magnetic
field around a coil if the current through the
conductor is increased from 1.0 A to 2.5 A?
(Hint Look at the 4 factors that affect
electromagnetic strength.)

Current
18
• What would happen to the field strength if the
number of turns in the coil of the electromagnet
were reduced by half and the current remained the
same? (Hint Look at the 4 factors that affect
electromagnetic strength.)
•
• What would happen to the strength of an
electromagnet if over time the conductor started
to corrode and increased the resistance of the
conductor?
•
• What would happen to the strength of the
electromagnet if the coiled conductor started to
unwind causing the diameter of the coil to
increase?
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