What is a magnetic field?http://education-portal.com/academy/lesson/what-is-a-magnetic-field.htmlhttps://www.youtube.com/watch?v=hFAOXdXZ5TM

Electricity and magnetism were regarded as unrelated phenomena until it was noticed that an electric current caused the deflection of the compass needle. Then, magnets were found to exert forces on current-carrying wires. The stage was set for a whole new technology, which would eventually bring electric power, radio, and television.

Magnetic Poles

What are fields?A field is a region of space

surrounding an object that can cause another object to experience a force (gravitational field, electric fields, magnetic fields)

Magnetic field: a 3D region of space around a magnet that causes a magnetic force on magnetic objects

Earth has a magnetic field both inside and surrounding it

A magnetic force is the force produced by the interaction of two magnetic fields.

The direction of the magnetic field outside a magnet is from the north to the south pole.Where the lines are closer together, the field strength is greater. The magnetic field strength is greater at the poles. If we place another magnet or a small compass anywhere in the field, its poles will tend to line up with the magnetic field.

Magnetic Fields

Magnetic field patterns for a pair of magnets when a. opposite poles are near each otherb. like poles are near each other

Magnetic Fields

How magnetic fields are created

http://education-portal.com/academy/lesson/how-magnetic-fields-are-created.html

The Law of MagnetismAll magnets have a north pole (N pole) and a south pole (S pole).

The law of magnetism:“Like magnetic poles repel and unlike poles attract each other”

Section 12.1Pole to Pole

When two magnetic poles are brought near each other, the pattern of field lines reveals whether the poles are like or unlike. You can use iron filings to see this pattern.Click the screen to reveal the field lines. Then, label each image using the terms below.

like polesunlike poles

Section 12.1Pole to Pole

When two magnetic poles are brought near each other, the pattern of field lines reveals whether the poles are like or unlike. You can use iron filings to see this pattern.Click the screen to reveal the field lines. Then, label each image using the terms below.

like poles

unlike poles

The Force of MagnetismIn 1600, it was found that Earth itself is a

lodestone with a north and south magnetic pole.

Magnets exert forces that seem to originate from the magnetic poles, and they can affect another magnetic object even without contact.

This is an “action at a distance” force. For example, if you suspend a magnet on a

string and bring another magnet close to one of its poles, the suspended magnet will rotate, even though there is no visible contact between the two magnets.

Magnetic fields are vector quantities — they have a magnitude (strength) and a direction.

Since the magnetic field is a vector quantity, it is represented by a vector arrow.

In diagrams, the length of the vector arrow represents the magnitude of the field, and the direction of the arrow represents the direction of the field at a point.

The magnitude of the field is greatest near the magnet and diminishes with distance.

Mapping Magnetic Field LinesTo represent the entire magnetic field surrounding

a magnet, it would be necessary to draw arrows at an infinite number of points around the magnet.

This is impractical. Instead, you can draw a few magnetic field lines

with a single arrowhead indicating the direction of the magnetic field.

It is important to remember that the magnetic field exists in three dimensions.

Magnetic Field PropertiesThe pole of a magnet that points

towards Earth’s north magnetic pole is labeled north and the other pole is labeled south.

Since the north pole of a compass needle points north Earth’s north pole must actually be a south magnetic pole since unlike poles attract (north and south)

Similarly, Earth’s south pole must actually be a north magnetic pole

see p. 548 for story

The north pole of a magnetic compass swings toward Earth’s north pole. What does this tell you about Earth’s north pole? How does this question relate to the direction of magnetic field lines?

Section 12.1

Discussion: Pole to Pole

Section 12.1Answers for Discussion Questions:

Sample answer: Earth’s north pole must really be a south magnetic pole. Field lines go from the compass’s north pole to this “south” pole, which is why magnetic field lines are directed toward south.

Properties of Magnetic Field LinesA bar magnet creates magnetic field lines that are

not parallel to each other and are closely spaced (dense) at the poles.

The magnetic field is non-uniform because the lines are not parallel.

If the field lines are parallel to each other, the magnetic field is uniform.

Magnetic field line diagrams have the following properties:

Exist in 3D surrounding a magnet and are more intense at the poles

magnetic field lines are continuous loops that never cross

inside the magnet, the magnetic field lines point from the south pole to the north pole

outside the magnet, the magnetic field lines point away from the north pole toward the south pole

the closeness of the lines represents the magnitude of the magnetic field (the closer the lines are together, the stronger the magnetic field)

if the field lines are parallel, the magnetic field is uniform

HOMEWORKP.552 questions #1,6

Tesla vs Edisonhttps://www.youtube.com/watch?v=gJ1Mz7k

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