"Magnetic Phenomenon: Magnetic Field" Electricity and Magnetism PPT (Magnetic Field in Lesson 2)

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"Magnetic Phenomenon: Magnetic Field" Electricity and Magnetism PPT (Magnetic Field in Lesson 2)

Part One: Knowledge Management

1. magnetic field

Definition: There is a substance around the magnet that can deflect the magnetic needle. We call this substance a magnetic field.

Basic properties: It produces a magnetic force on the magnet placed inside it.

Direction: At a certain point in the magnetic field, when the small magnetic needle is stationary, the direction pointed by the North Pole is the direction of the magnetic field at that point.

2. Magnetic field lines

Magnetic induction lines: The curves that vividly describe the magnetic field are called magnetic induction lines.

(1) Direction: The tangent direction of any point on the magnetic field line is the direction of the magnetic field at that point.

(2) Strength: The sparse distribution of magnetic field lines means that the magnetic field here is weak; the dense distribution of magnetic field lines means that the magnetic field here is strong.

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

3. geomagnetic field

The earth itself is a huge magnet, and the magnetic field around the earth is called the geomagnetic field. The geographical south and north poles are opposite to the geomagnetic south and north poles; the geographical south pole and the geomagnetic north pole are somewhat deviated, as are the geographical north pole and the geomagnetic south pole. This deviation is called magnetic declination, which was first discovered by Shen Kuo, a scholar in the Song Dynasty of my country.

Magnetic Phenomenon and Magnetic Field PPT, Part 2 Content: Classification and Exploration

Type one: magnetic field

[2018•Hubei Enshi Prefecture]Which of the following statements about magnetic fields is wrong (　D　)

A. The magnetic field around a magnet is real

B． Magnetic field lines are virtual closed curves used to describe magnetic fields.

C. There is a magnetic field around a current-carrying conductor

D. The N pole of a compass on the ground always points to the geographical South Pole.

[Analysis] There is a magnetic field around the magnet, and the magnetic field is real, so statement A is correct; magnetic field lines are a physical model introduced to vividly describe the distribution of magnetic fields, and are virtual closed curves, so statement B is correct; according to Oersted The experiment shows that there is a magnetic field around the current-carrying conductor, so statement C is correct; the earth is a big magnet, and the geomagnetic north and south poles are opposite to the geographical north and south poles. Therefore, when the compass is stationary, the N pole of the compass points to the geomagnetic south pole, which is the geographical north pole. Therefore, D's statement is wrong. Choose D.

Type 2: Geomagnetic field

[2018•Tianjin Nankai District]If the hypothetical geomagnetic field is generated by a large magnet inside the earth, among the four schematic diagrams shown below, the one that can reasonably describe this large magnet is (　A　)

[Analysis] The earth is a large magnet. The shape of the geomagnetic field is similar to that of a bar magnet. The north and south poles of the geomagnetic field are opposite to the geographical north and south poles. They do not completely coincide. There will be a magnetic declination, that is, the geomagnetic north pole is near the geographical south pole. , so A is correct. Therefore choose A.

[Summary] The earth is a big magnet, and the magnetic field surrounding the earth is called the geomagnetic field. The shape of the geomagnetic field is similar to that of a bar magnet. The geomagnetic north pole is near the geographical south pole, and the geomagnetic south pole is near the geographical north pole.

Magnetic Phenomenon and Magnetic Field PPT, Part 3: In-person Evaluation

1. [2019• Chengde, Hebei Province (The black end of the magnetic needle represents the N pole) (C)

A. A B. Second

C. C D. Man

2. [2018•Suzhou, Jiangsu]In an experiment to explore the magnetic field around a hoof-shaped magnet, the teacher placed the glass plate flat on the magnet, evenly sprinkled a layer of iron filings, tapped the glass plate, and the iron filings They will be arranged in an orderly manner, as shown in the picture. The analysis of relevant phenomena in the experiment is wrong (A)

A. The purpose of scattering iron filings is to reveal the magnetic field that did not exist before.

B． Iron filings are magnetized in a magnetic field into small magnets

C. Tap the glass plate gently, and the iron filings will separate from the glass plate due to their inertia.

D. Tap the glass plate gently. After the iron filings are separated from the glass plate, there is no friction. The iron filings are arranged in an orderly manner under the action of magnetic force.

[Analysis] There is always a magnetic field around the magnet. The distribution characteristics of the magnetic field around the magnet can be displayed with the help of fine iron filings, but it does not display the non-existent magnetic field, so A is wrong; the iron filings are not magnetic originally, but under the action of the magnetic field, they can Obtaining magnetism means that it is magnetized, so B is correct; the iron filings have small mass, small inertia, and the state of motion is easy to change, so tap the glass plate, and the iron filings will separate from the glass plate due to their inertia, so C is correct; the iron filings are affected by Under the action of the magnetic field, tap the glass plate, and after the iron filings are separated from the glass plate, there is no friction, and the iron filings gradually arrange themselves in order, so D is correct.

3. [2019 • Beijing Wang Chong, a scholar of the Eastern Han Dynasty, recorded in "Lunheng": "Sinan's ladle, thrown to the ground, is a guide." Regarding the compass, the correct one of the following statements is (B)

A. Some compasses have only one magnetic pole

B． A freely rotating compass, when stationary, points to north due to the effect of the geomagnetic field.

C. Compass pointing will not be disturbed by nearby magnets

D. There is no magnetic field around a compass

Magnetic Phenomenon and Magnetic Field PPT, Part 4: Layered Operations

1. [2019•Shandong Linyi]About the magnetic field lines, which of the following statements is correct (C)

A. Magnetic field lines are real curves in the magnetic field

B． Magnetic field lines only exist outside the magnet

C. Where the magnetic field lines are denser, the magnetic field is stronger

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

[Analysis] Magnetic field lines are directional curves introduced by people in order to intuitively and vividly describe the direction and distribution of magnetic fields. They are not real curves that objectively exist in the magnetic field, so A is wrong; inside the magnet, there are also magnetic Lines of induction, so B is wrong; the density of the lines of magnetic flux reflects the strength of the magnetic field. Where the lines of magnetic flux are denser, the magnetic field is stronger, so C is correct; inside the magnet, the lines of magnetic flux start from the S pole of the magnet. Return to the N pole, and outside the magnet, it starts from the N pole of the magnet and returns to the S pole, forming a closed curve, so D is wrong.

2. [2019•Nanning, Guangxi]What is drawn in the picture is a schematic diagram of the magnetic field lines around the magnet. The magnetic poles of the magnet are (　B　)

A. A is the N pole, B is the S pole

B． A is the S pole, B is the N pole

C. A is the N pole, B is the N pole

D. A is the S pole, B is the S pole

3. [2018•Wenzhou, Zhejiang]The earth is a big magnet. Place a freely rotating compass on the equator on the earth's surface and point as shown in the figure when stationary. Which of the following compass directions is correct (C)

4. [2018•Jiangsu Changzhou]Three magnets are adjacent. The distribution of magnetic field lines between the magnetic poles is as shown in the figure. The D end is the N (optional "N" or "S") pole, and the B end is N (optional "N" or "S") pole.

[Analysis] It can be seen from the figure that the magnetic field lines between the middle magnet and the magnet on the right are repulsive. It can be seen from the mutual repulsion of the magnetic poles with the same name that the D end of the middle magnet is the N pole and its C end is the S pole. As can be seen from the figure, the middle magnet The magnetic field lines between the magnet and the magnet on the left are attractive. It can be seen from the magnetic poles with different names that attract each other. The B end of the magnet on the left is the N pole.

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Update Time: 2024-10-03

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