"Magnetic Phenomenon" Electromagnetic Phenomenon PPT Courseware 3

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"Magnetic Phenomenon" Electromagnetic Phenomenon PPT Courseware 3

1. Magnetic phenomena

At the beginning of the 1st century AD, Wang Chong, a scholar of the Eastern Han Dynasty, recorded in "Lunheng" that "Sinan's ladle was thrown to the ground and its guide was used."

The Chinese have long used compasses (compasses) to indicate direction during navigation.

1. Magnets can attract iron, cobalt, nickel and other substances.

2.1 The two parts with the strongest attraction ability on the magnet are called magnetic poles.

(Each magnet has two poles)

2.2 For a magnet that can rotate freely, the magnetic pole that points to the south pole or S pole when it is stationary is called the south pole or S pole, and the magnetic pole that points to the north is called the north pole or N pole.

3. The law of interaction between magnets: magnetic poles with the same name repel each other, and magnetic poles with different names attract each other.

4. Some objects can acquire magnetism under certain conditions, a phenomenon called magnetization.

2. Magnetic field

1. There is an invisible and intangible substance surrounding the magnet called a magnetic field.

think

If a magnetic needle is placed near a magnet and its direction deflects, what does it mean?

The magnetic needle is acted upon by a force.

Force is the effect of an object on an object. If the magnet and the magnetic needle are not in contact, how can there be a forceful effect?

2. In physics, the direction of the force exerted by the magnetic field on the small magnetic needle, that is, the direction pointed by the north pole when the small magnetic needle is stationary, is defined as the direction of the magnetic field at that point.

Experiment 1

(1) Do the magnetic needles point in the same direction?

(2) Are the directions of the magnetic forces on the small magnetic needles the same?

(3) What properties of the magnetic field does this phenomenon reflect?

Experiment 2

Place a piece of plexiglass on top of the magnet, sprinkle some iron filings evenly on the glass, tap the glass and observe.

The magnetized iron filings are like small magnetic needles. Under the action of the magnetic field, they vividly display the distribution of the magnetic field.

3. We draw the arrangement of the small magnetic needles in the magnetic field with a curve with an arrow to vividly describe the magnetic field. Such a curve is called a magnetic field line.

①The direction of any point on the magnetic field line is the same as the direction of the magnetic field at that point.

② Magnetic field lines are a method of describing magnetic fields and do not exist.

③The magnetic field lines outside the magnet all start from the N pole of the magnet and return to the S pole.

3. Geomagnetic field

think

The rotation of the magnetic needle is the result of the action of the magnetic field. So compasses can guide north and south all over the world, but whose magnetic field is exerting the action?

1. The magnetic field that exists around the earth is called the geomagnetic field.

2. Studies have shown that the geomagnetic field has a shape similar to that of a bar magnet.

3. Geomagnetic field characteristics

The geomagnetic N pole is near the geographical South Pole;

The geomagnetic S pole is near the geographical North Pole.

The geographical poles are opposite to the geomagnetic poles and do not exactly coincide.

practice

1. Mark the names of the magnetic poles and the directions of the magnetic fields at points A and B.

2. The correct statement about magnetic field lines is ( )

A. Magnetic field lines are formed by small iron filings

B． There are many curves in the magnetic field, these curves are called magnetic field lines

C. The small magnetic needle only experiences force on the magnetic field lines and does not receive force between the two magnetic field lines.

D． Magnetic field lines are imaginary by people in order to vividly describe the distribution of magnetic fields. They do not actually exist.

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Update Time: 2024-07-06

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