Transcript L46-magnets-Jan15.

What are we doing Today?
Ch. 5  Magnetism
• Homework Questions Check
• Hand in Lab 41-42
• Chapter 5 Notes
• In class questions & homework
p. 174 Question 19 (b,c)
textbook
p. 174 Question 20 (a,b)
Magnetism (Chapter 5 - p.163)
Magnet – An object that can
attract other objects
containing iron, cobalt or
nickel
Magnetic Poles
Iron filings
N
The strength of a magnet is
concentrated at the ends,
called north and south
“poles” of the magnet.
S
W
N
S
Bar magnet
N
S
N
E
Compass
If you cut a magnet in half,
you get 2 magnets!
Magnetism (Chapter 5 - p.163)
Magnetic Field – Is the area of
space in which the magnetic
force of a magnet can act on
another magnet.
Magnetic Fields
*Magnetic field lines move away from
north poles and toward south poles.
Magnetic Field Lines
We can describe
magnetic field lines
by imagining a tiny
compass placed at
nearby points.
The direction of the
magnetic field B at
any point is the same
as the direction
indicated by this
compass.
N
S
Field Lines Between Magnets
Unlike poles
N
Attraction
S
Leave N and
enter S
N
Like poles
N
Repulsion
Ferromagnetic Substance (p.167)
Ferromagnetic materials are materials that
have magnetic properties similar to those
of iron. They can become permanently
magnetized. Examples of ferromagnetic
materials are nickel and cobalt.
ELECTROMAGNET
A magnet with a field produced by an electric current
Electromagnetism
a moving charge (electricity)
produces a magnetic field
•
More coils of wire=
more current =
stronger magnet
•
Bigger battery =
stronger magnet
• Magnetic field pattern around
a straight wire.
• The resulting magnetic field
lines form concentric circles
around the wire.
The Right-Hand rule can be
used to predict the direction
of the magnetic field
Magnetic field around a wire carrying current
The Electromagnet
 By the Right Hand Rule, a coil of wire with current
flowing in it will create a magnetic field
 The strength of the magnetic field depends on
 The amount of current in a wire – More current
means stronger magnetic field
 The number of turns in the coil – More turns means
stronger magnetic field
 The material in the coil – Magnetic materials like
iron and steel make the magnetic field stronger
The Electromagnet
• A simple electromagnet can be made by
coiling some wire around a steel nail, and
connecting a battery to it.
• As current rotates around the nail, a magnetic
field is created with the North pole at the
bottom and the South pole at the top
The Electromagnet
• Electromagnets are found in many everyday
objects such as
– Motors and generators
– Doorbells
– Speakers
– Hard drives
– VHS and Audio cassette tapes
– Telephones
Solenoid (p.169) EST
• Solenoid: Is a cylindrical coil of live wire.
Magnetic Field of a Solenoid(EST)
Look at p.169 in your
textbook
Classwork
• P. 174  Questions 21-25
Exit Question(s)
Draw the following circuits and which of the circuits below are
connected in series, and which are connected in parallel?
Number 1
Answer: Parallel
Number 2
Answer: Series
Number 3
Answer: Parallel
Number 4
Answer: Series
The circuit is composed of a 6.0-V battery connected to a 10-Ω
resistor. It includes an ammeter and a voltmeter connected to the
resistor terminals.(look up in chapter 5 on diagrams of circuits).
a) Draw the circuit diagram, including the measuring instruments.
Exit Questions
1) The potential difference in a circuit is determined to
be 10 volts. If the resistance is 5 ohms, what must the
current intensity be?
The potential difference in a circuit is
determined to be 10 volts. If the resistance is 5
ohms, what must the current intensity be?
Answer:
1. Determine what you are looking for.
2. List what you know and don’t know.
• V = 10 Volts
• R = 5 ohms
• I =?
3. Use equation
V = R x I
Solve for I, so I = V/R
4. I = 10 Volts / 5 ohms = 2 A
Answer: The current intensity will be 2 A (Amps)
What To Do Now?