Transcript Magnetism and Electricity

Magnetism and Electricity
Quick Write:
Write about how you use electricity in your home.
Were you surprised by any of the
objects you tested?
Look at your lists. Is there anything
you notice
that is the same about all the things
listed in
the column for the things that stick?
Are there any metals in the things
that don’t stick column?
What do you think is different about
the metal items in the
1st column compared to the 2nd?
There is only one common kind of metal
that magnets stick to-iron. Sometimes it’s
mixed with other metals to make steel.
Quick Write
• Can you think of a general rule about what
magnets stick to?
• What about the “rock” that stuck?
(It is magnetite, which is rich in iron!)
Magnet Properties
• What made you sure these objects were iron or steel?
• Which objects you tested in the room surprised you?
• Were there any objects you thought might be iron, but
were not?
• Did you find any steel that was hidden by paint or
something else? How do you know?
Magnet Properties
• How do magnets and iron objects work
together?
• Can the force of magnetism go through
materials?
• Did you discover:
– Some steel objects seem to become temporary
magnets when they are touching a magnet.
– Magnets can attract a piece of steel right through
a piece of paper or plastic.
Magnet Properties
• Does an object have to touch a magnet to become a
temporary magnet?
• Can magnets attract steel through all kinds of materials?
• Can a magnet attract a paper clip through a thin sheet of
metal like copper or aluminum?
• Can a magnet attract a paper clip through a large, thin
sheet of steel, like the side of a cabinet?
• Did you discover?
– Magnetic force acts through all the objects, except those with a
large surface area made of iron.
– And when the distance or thickness of an object is great, the
force may not be strong enough.
Quick Write
• Is the force of magnetism stopped by any
materials? How do you know?
(You could draw a picture!)
Breaking the Force
• How can the strength of the force of attraction
between two magnets be measured?
• From earlier observations, we thought that
the force of attraction didn’t work if the
magnets were too far apart. How could we be
sure that observation is true?
How many washers will break the
force?
Group
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Washers
How many washers will break the
force?
• Why do we have different results?
Technique
• Does it make a difference where you place the
washers in the balance?
• Does it make a difference how you can place
the washers in the balance?
• Does it make a difference if you drop the
washers on the balance?
• Lets decide on how we are all going to do this
now so we can collect data that is the same.
How many washers will break the
force?
Group
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Washers
Remember our
norms for putting washers in:
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Breaking the Force
• How many washers did it take to break the
force with 1 spacer?
• How many spacers were used when it took
about 4 washers to break the force?
• How can you use a graph to predict?
• So: What happens to the force when you put
spacers between 2 magnets?
• As spacers (distance) increases, the force of
attraction decreases!
REVIEW
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Magnets stick only to i____.
Two magnets can a_____ or r______.
A force is a p_____ or a p____.
The magnetic f______ acts through space and
most materials.
• The magnetic force of attraction between two
magnets d________ with distance.
• The greater the distance between the two
magnets, the w______ the force of attraction.
Detecting Magnets
• What role did iron play in each kind of magnet
detector?
• Why do you think the filings work like they did?
• Do you think the compass has iron in it, why?
• How did the compass help you locate the magnet
in the box?
• Quick Write:
• What was the best detector? Why?
Lighting a Bulb
• Anything that uses electricity to do something
is an electricity receiver.
• The light bulb produces light when it receives
electricity as it flows through the whole
circuit.
Lighting a Bulb
• The pathway though which the electricity
flows from the D-cell to the light and back to
the cell is a circuit.
• “Circuit” sounds like circle and has a similar
meaning. The circuit must form a complete
circle from one end of the D-cell back to the
end of the D-cell for the electricity to flow.
• We call the individual items in the circuit the
components.
Lighting the Bulb
The current flows
from the negative
end of the battery
(flat end), through
the circuit, and to
the positive end
(end with bump).
Lighting the Bulb
Now try with just ONE wire!
Lighting the Bulb
Review
• You can’t see electricity. How do you know when
it is flowing in a bulb circuit?
• How many wires connect to the battery, and
where do they connect to make a complete
circuit?
• How did you get the bulb to light with only 1
wire?
• The part of the bulb that makes light is the
filament. When electricity goes through it, it gets
so hot that it gives off light.
Quick Write
• What components are needed to make a
complete circuit?
Conductors and Insulators
• An object like the steel nail, which makes a
closed circuit and lets the electricity flow, is
called a conductor.
• An object like the plastic straw, which cannot
close a circuit- one that does not let the
electricity flow- is called a nonconductor, or
insulator
• So: Electricity flows though conductors, not
insulators.
Quick Write
• Why is it helpful to know whether an object is
a conductor or an insulator?
Advanced Connections
• How can we get 2 bulbs to light at the same
time?
• Need: 1 circuit base, 1 D-cell, 1 switch, 3 short
wires, 2 bulbs in holders
• When 2 bulbs are connected in one big circuit,
so that the electric current has to go through
all the components one at a time, that is a
series circuit.
• Why are the lights dim?
• How can we make 2 bulbs bright?
• May use: another D cell, cell holder, and wire
Parallel Circuits
• Last time we lit 2 bulbs with 1 battery, but
they were dim.
• We learned: A circuit with 1 path is a series
circuit. Components in a series “share” the
electric energy.
• D-cells must point in the same direction to
work.
• How can we light 2 bulbs brightly with just 1
battery?
• You may use: 1 D-cell, 1 cell holder, 2 bulbs, 2
long wires, 4 short wires
• So: Whenever a circuit splits and goes to two
or more components, that is a parallel circuit.
The bulbs are said to be in parallel.
More complex Circuits
• What could you do with a switch?
• What could you do with another cell?
• Other ideas to try:
– In a circuit with 2 bulbs in parallel, where would you put a
switch to turn one bulb off?
– Where would you put the switch to turn both bulbs off?
– If you are using Design A, what do you do to add a 3rd
bulb?
– Would another D-cell affect the brightness of 2 bulbs
connected in parallel?
– How many bulbs in parallel can one D-cell light?
Electromagnet
I am thinking about a big
old junkyard crane that I
once saw. The crane used
a big magnet to lift cars
and put them on train
cars. The crane operator
could turn the magnet on
and off! Can you make a
miniature junkyard crane
that turns on and off?
•Electromagnetic Crane
• An electromagnet is a piece of iron with insulated
wire wrapped around it. While electric current is
flowing through the wire, the piece of steel
becomes a temporary magnet.
• How can we make the best electromagnet so we
can compare results?
– Use the same number of winds
– Pick up washers with the head of the rivet
– Count the washers lifted to determine the strength of
the magnet
Quick Write
• How can you make a magnet that turns on
and off?
• How else can you change the strength of an
electro magnet?
– Change the number of winds
– Add another D cell
– Use thicker wire
Electromagnet
• Does it matter how tight the coils are?
• What would happen if you wound half the
coils one way and half the other way?
• What would happen if you added a D-cell?
• What would happen if you made it a parallel
circuit?
• What would happen if you used thicker or
thinner wires?
The Telegraph
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In the summer of 1860, if you had the money, you could send a message from
St. Joseph, Missouri to Sacramento, California in 10 days. That’s how long it
took a good rider and a fast horse to cover the distance. To keep the message
moving at this rapid pace, several riders and over 1000 horses were used. This
was the Pony Express, the fastest way to communicate across the 1800 miles
of the western frontier. However, it lasted only 18 months. In 1861 the
telegraph crossing the country was completed, and the Pony Express faded
into history.
The telegraph story starts in 1844, when Samuel Morse sent the first message
by telegraph from Baltimore, Maryland to Washington, D.C.. People couldn’t
actually hear each other talk on the telegraph, as you can when you use a
telephone. The telegraph made clicks at the receiving end each time the key
(switch) was pressed at the sending end. Morse developed a code that lets
people make letters of the alphabet out of patterns of clicks and pauses. In
this way words were sent from city to city. In it’s day the telegraph was the
most important tool for rapid communication. It wasn’t until the invention of
the telephone in 1876 that the telegraph began to decline in importance.
• Can you explain how the telegraph works?
• What were some of the problems you
encountered in telegraph communication, and
how might you improve this system?