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Magnetism- a force of attraction or repulsion due to the arrangement of electrons. Mag Lev vid.

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Presentation on theme: "Magnetism- a force of attraction or repulsion due to the arrangement of electrons. Mag Lev vid."— Presentation transcript:

1 Magnetism- a force of attraction or repulsion due to the arrangement of electrons.
Mag Lev vid

2 Why are some materials magnetic?
Iron, nickel and cobalt are magnetic because the electrons in the material have the same axial and orbital spin, creating a net electrical force. Cancellation of this effect occurs in most materials since the electron movement is random in most matter. link

3 Magnetic Domains- a microscopic magnetic region composed of a group of atoms whose magnetic fields are aligned in a common direction.

4 There are NO Magnetic Monopoles…
No matter how many times a bar magnet is cut in half, there is always a north and south pole, even in the smallest piece.

5 Magnets-like poles repel opposite poles attracts
video All magnets have north & south poles. North poles attracts South poles, South poles attract North poles. North poles repel North poles, South poles repel South poles. In general, magnetic fields originate on North poles and terminate on South poles.

6 Compass Needles are Tiny Magnets
link2 Compass needles are just small magnets which twist into alignment with the Earth’s magnetic field The Earth’s magnetic field is caused by the movement of charged particles in the core.

7 Earth’s magnetic reversals

8 Magnetic Fields are defined as a region in which a magnetic force can be detected.

9 Magnetized Iron filings line up around bar magnet.
This shows the shape of the magnetic field. Like all field forces, greater distance from the magnet reduces the field strength by an inverse square.

10 Just as an electric charge is surrounded by an electric field, the same charge is also surrounded by a magnetic field if 1) it is moving and/or 2) if the electron spins are aligned.

11 Moving Charges, like current in a wire, creates Magnetic Fields.
Proof: Compasses (bar magnets) line up in circles around a wire carrying current. link3

12 Magnetic Field Patterns around a Current Carrying Wire

13 What is an Electromagnet?
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of current through a wire wrapped around an iron core. The iron is temporarily magnetized when there is a current. Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays and speakers. Making an Electromagnet

14 How can we increase the strength of an Electromagnet?
Increase number of turns of wire 2. Increase the current and/or voltage 3. Use more iron in the core

15 On the flip side, an electric current can be created in a wire by changing the magnetic field.
video Electric current can be produced in a looped wire simply by moving a wire near a magnet or via versa. Rapidly changing the magnetic field induces a change in the electric field causing electrons to move (current is produced). The voltmeter reflects the amount of current produced by the oscillating magnetic field inside the loop.

16 Electromagnetic Induction
What happens to the current produced if the magnetic flux is increased? Current is increased What will be the ammeter reading if the coil number is increased to eight? 2 loops = 1 A 4 loops = 2 A 6 loops = 3 A 8 loops = 4 A 2x coils = 2x I

17 Magnetic Fields exert force on moving charges and on current-carrying conductor.
video A wire carrying current has charges moving in it. Therefore, if a current-carrying conductor is in an external magnetic field, it experiences a force. I

18 Electric Motors: Convert electrical energy into mechanical.
video Here’s how: Current creates magnetic field, which interact with secondary magnetic field (usually a stationary magnet), causing motion due to the attraction and repulsion between the two changing fields. Motor explained video x

19 Computers, cell phones, credit cards and other devices that store information in the orientation of magnetic domains should never be brought near electric motors. Since the motor produces a magnetic field, it can interact with the stored data, causing devices that store information to lose it.

20 Never put a magnet near a TV or computer screen!
Older screens form images by firing a steam of electrons which negatively charges the screen. The magnet will deflect the electrons, thus distorting the image, often permanently.

21 Opposite of a motor is a generator, which uses electromagnetic induction to convert mechanical energy to electrical energy. applet Video Coils Rotating in a Magnetic Field Induce a Current

22 Step-down Transformer
A transformer is an electrical device that takes electricity of one voltage and changes it into another voltage.

23 Energy in = Energy out In this step-up transformer, the number of turns of the coil are increased, thus increasing current and therefore, voltage. The greater length of wire create greater resistance but not proportionately. Ultimately, the power is the only variable conserved.

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