Transcript Lets look at the magnetic field….

The Physics of
Electricity and
Magnetism
Making a
Magnet
9-12 Science Std: Phys 5h, 5j
First, a quick review about magnets
Magnets are usually metals or ceramic
•They come in many shapes
•Horseshoe magnets
•Flat magnets that can go on a
refrigerator
•Bar magnets
First, a quick review about magnets
But these magnets all have some things in common…
•They all attract things that contain iron
•Nails, paper clips, etc
•They are most strongly
attracted to the ends of the
magnets – called the poles of
the magnet
•There are 2 poles – called the
North Pole and the South Pole
•Opposite poles attract, same
poles repel
•Lines of force (magnetic field) surround
the magnet going from north to south
First, a quick review about magnets
And you have heard of electromagnets…..
•Wrap some wire around a
nail and put current through
it…
•And you get a magnet just
like a bar magnet with a north
and a south pole…
N
S
•But how does a bunch of electrons moving through a wire
make a magnetic field?
How does this work?
Scientists in the late 1700’s started working on this…
•They thought that electricity
and magnetism worked
together somehow
•But no one had an idea how
they worked together
•So they didn’t know where
to start….
How does this work?
Then in 1820, an experiment was done…..
•Hans Oersted did an
experiment with a
wire and a compass
•He held a wire next to a
compass and ran a current
through it
How does this work?
Then in 1820, an experiment was done…..
•When the current
was turned on….
•The needle of the compass
turned away from pointing
towards North
How does this work?
Then in 1820, an experiment was done…..
•When the current
was turned off
•The needle went back to pointing
to North
•Disc 19 Demo 8
How does this work?
Why did the compass needle move?
•When an electrical current flows through a wire
•A Magnetic field is created by the moving electrons that
wraps around the wire
How does this work?
Why did the compass needle move?
•Here is a video demonstration showing the magnetic
field around a wire…..
•Disc 19 Demo 9
Lets look at the magnetic field….
Which way does the magnetic field go?
•From the
video we
saw that the
iron filings
made a
circle
around the
wire
Lets look at the magnetic field….
Which way does the magnetic field go?
•We also saw
how the iron
filings take
shape around
a coil of wire…
Lets look at the magnetic field….
But why does the magnetic field have these shapes?
•When the
current goes
through the
wire
•A circular
magnetic field
wraps around
the wire using
the Right
Hand Rule
Lets look at the magnetic field….
What is the Right Hand Rule?
•Imagine your pencil is
a wire carrying an
electrical current
•Now picture the
current going from the
bottom of the pencil to
the top….
Lets look at the magnetic field….
What is the Right Hand Rule?
•Now take your right
hand
•And wrap it around the
pencil with your thumb
pointing in the direction
the current is going
Lets look at the magnetic field….
What is the Right Hand Rule?
•Your fingers are
wrapped in the
direction of the
magnetic field
Lets look at the magnetic field….
What is the Right Hand Rule?
•We can see this
better in the video
demonstration
using a wire and a
compass….
•Disc 19 Demo 7
So now lets try it ourselves…..
Using the Right Hand Rule…
•If we have a wire
like the one here…
•And the current is
flowing from top to
bottom….
•Which way is the
magnetic field
going to go?
So now lets try it ourselves…..
How about this one….
•If we have a coil of wire…..
•And the current is flowing
from top to bottom….
•Which way is the magnetic
field going to go?
•So this will look just like a
bar magnet!
•Disc 19 Demo 10
Important things to remember…
•Electrical current
makes a magnetic
field
N
S
•The more the
current, the stronger
the magnetic field
•The direction of the magnetic
field is shown using the Right
Hand Rule
Important things to remember…
•Current through a coil of
wire makes an
electromagnet
•Electromagnets are just
like regular magnets
•They have north and
south poles
N
S