Transcript electrical current

The Physics of
Electricity and
Magnetism
Magnetic
Induction
of Current
9-12 Science Std: Phys 5h
It was a very special discovery….
When Oersted found that current in a wire made
a magnetic field…..
Physics
was
changed
from
then
on….
It was a very special discovery….
But then scientists asked…..
If electricity can
make a magnet…
Can a magnet make
electricity?
Then in 1831…….
Two scientists found a way to do it!
In England
And here in the U.S
Michael Faraday
Joseph Henry
They both found a way to do it at the
same time in different places
Before 1831….
The only way to make an electric current was..
Dissolving
special
metals in
acids
Which was
very
expensive
and
dangerous
But now…..
We can make electricity any time, anywhere!
To make Electricity we need:
N
S
A
magnet
And a
piece of
wire.
Wait a second……
Didn’t we say before….
N
Electricity
(a current)
S
To make a magnet we need:
Yes, we
did!
And a
piece of
wire.
Wait a second……
In fact, we said….
As long as charged particles are moving…
A magnetic field
is made using the
Right Hand Rule
S
And the current
is going
through a wire
N
Like with an
electrical
current
Wait a second……
But now we are saying…..
To make an electrical current……
You take a
magnet
S
And you use a
piece of wire…
N
And you get
an electrical
current!
So how does this work…..
When we made the magnetic field….
The charged particles were moving…
Which is an electrical current
And they were moving because of an electric field or
voltage potential…
So how does this work…..
So now to make the electrical current…..
We still need some movement…..
But this time instead of moving the current to
make the magnet….
So how does this work…..
So now to make the electrical current…..
We still need some movement…..
We move the magnet to make the current!
N
S
So how does this work…..
When we move the magnet across the wire….
S
And the voltage
makes an
electrical current
in the wire
N
The lines of
the magnetic
field move past
the wire….
As the
magnetic
field lines
pass the wire
It makes a
voltage
potential in
the wire
Let’s see this in action….
Demonstration time!
On the front desk is a
meter called an
galvanometer
This is a meter that
can measure the
amount of current or
voltage
And it can show the
direction the current
is flowing
Let’s see this in action….
Demonstration time!
The more the needle
moves on the meter…
The more current is
flowing in the wire
The direction the
needle moves…
Shows which direction the current is moving
Let’s see this in action….
Demonstration time!
The ammeter is hooked
up to a coil of wire
We use a coil
because the more
wire – the more
current is made
Let’s see this in action….
Demonstration time!
Then we take a magnet
and move it through the
coil of wire…
While the magnet is
moving, watch what
happens to the
ammeter……
N
S
Can the amount of current change?
Yes it can……
The amount of current depends on…
The amount of wire
A little wire……
Makes a little current
A lot of wire…..
Makes a lot of current
Can the amount of current change?
Yes it can……
The amount of current depends on…
The amount of magnetic field
A small magnet
A big magnet
N
N
S
S
Makes a small current
Makes a big current
Can the amount of current change?
Yes it can……
The amount of current depends on…
How fast the magnet moves
Magnet moves slowly
N
S
You get a small current
Move the magnet fast
N
S
And you get a large current
Can the amount of current change?
Yes it can……
So remember…….
The amount of current depends on:
1. The amount of wire
2. The size of the magnet
3. And how fast the
magnet moves
N
S
So where can we use this?
Where are some places we can use this?
But we can also use
it to power a
flashlight without
batteries
To make
electricity that
we use at
home
Important Points…..
Changing magnetic fields make electric fields
Electric fields are voltages
Electric fields or voltages can be seen by
using a voltmeter
Electric fields or voltages can make
electrical currents in conductors
Electrical currents in conductors can be
seen by using an ammeter or a voltmeter
Homework for tomorrow’s activity:
You will need a cell phone
Turn off the cell phone and take out the battery
On the battery you will find 2 numbers:
xxx mAh – This the number of milliamps that
your cell phone battery will make for 1 hour
(mine is 950 mAh)
xx V – This is the voltage that your cell
phone battery makes (mine is 3.7 V)
Bring these numbers to class tomorrow
So if you would like to take a closer
look…..
You can come up and give it a try