"Electricity Generates Magnetism" Electricity and Magnetism PPT

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"Electricity Generates Magnetism" Electricity and Magnetism PPT

Part One: Knowledge Management

1. Oersted experiment

Conclusion: There is a magnetic field around the current-carrying wire, and the direction of the magnetic field is related to the direction of the current.

Significance: Oersted's experiment was the first to reveal the close connection between electrical phenomena and magnetic phenomena, that is, the magnetic effect of electric current.

2. Magnetic field of energized solenoid

Magnetic field characteristics: The magnetic field outside the energized solenoid is the same as the magnetic field of the bar magnet. Its two ends are equivalent to the two magnetic poles of the bar magnet. The polarity of its two ends is related to the direction of the current in the solenoid.

Magnetic pole judgment: Ampere's rule: As shown in the picture, hold the solenoid with your right hand and let your four fingers point in the direction of the current in the solenoid. Then the end pointed by your thumb is the N pole of the solenoid.

Note: (1) The magnetic field lines outside the energized solenoid start from the North Pole and return to the South Pole, but the magnetic field lines inside the solenoid point from the South Pole to the North Pole.

(2) The fundamental factor that determines the polarity of the magnetic pole of the energized solenoid is the direction of the current in the energized solenoid, not the winding method of the wire on the energized solenoid and the connection of the positive and negative poles of the power supply.

Electromagnetic PPT, Part 2: Classification and Research

Type One: Oersted Experiment

[2019•Shandong Weifang]As shown in Figures A, B, and C, the experiment explored is called the Oersted experiment. A comparison of Figures A and B shows that there is a magnetic field around the current; a comparison of Figures A and C shows that the direction of the magnetic field of the current is related to the direction of the current. This phenomenon is called the magnetic effect of electric current. The function of the small magnetic needle in the experiment is to test the existence of the magnetic field around the current.

[Analysis] As shown in Figures A, B, and C, the experiment under investigation is called Oersted's experiment. From the figure, we can see that there is current in the wire in Figure A and the small magnetic needle deflects. There is no current in the wire in Figure B and the small magnetic needle does not deflect. Compare Figures A and B illustrate: There is a magnetic field around the current. The direction of the current in the wires in Figures A and C is different, and the deflection direction of the small magnetic needle is different, which means that the direction of the force on the small magnetic needle is different, and the direction of the magnetic field is different. Comparing Figures A and C, it shows that the direction of the magnetic field of the current is related to the direction of the current. This phenomenon is called the magnetic effect of electric current. Using the conversion method, the presence of the magnetic field around the current is tested through the deflection of a small magnetic needle.

[Method Summary] Oersted's experiment shows that there is a magnetic field around the energized wire, and the direction of the magnetic field is related to the direction of the current, so it can be judged based on this analysis.

Type 2: Polarity of energized solenoid

[2018•Shanghai]Among the following items, the direction of the N pole of the small magnetic needle and the direction of the magnetic field lines of the energized solenoid are both correct (A)

[Analysis] It can be seen from the figure that the direction of the current and the winding method of the coil are the same in the four pictures, and the current flows in from the front right and flows out from the rear left. According to Ampere's rule, the direction pointed by the bending of the four fingers is the direction of the current, then the maximum The left end of the energized solenoid with your thumb pointing to it is the N pole, and the right end of the solenoid is the S pole; outside the magnet, the direction of the magnetic field lines is from the N pole to the S pole, and the direction of the magnetic field lines is to the right, so C and D are wrong; It can be seen from the interaction between magnetic poles that the lower left end of the small magnetic needle is the N pole and the upper right end is the S pole, so A is correct and B is wrong. Choose A.

[Method Summary] Ampere's rule involves three directions: ① current direction; ② coil winding direction; ③ magnetic field direction. For examinations in this area, two of them are usually told directly or indirectly, and Ampere's rule is used to determine the third direction.

Electromagnetic PPT, the third part: evaluation in class

1. [2018•Panzhihua, Sichuan]Which of the following scientists’ discovery revealed the connection between electricity and magnetism for the first time (　C　)

A. Faraday b. joule

C. Oster D. ampere

2. [2018•Shandong Linyi]The direction of the small magnetic needle when it is at rest is as shown in the figure. It can be seen from this that (B)

A. Terminal a is the N pole of the energized solenoid, and terminal C is the positive pole of the power supply.

B． Terminal a is the N pole of the energized solenoid, and terminal C is the negative pole of the power supply.

C. Terminal b is the N pole of the energized solenoid, and terminal d is the positive pole of the power supply.

D. The b terminal is the N pole of the energized solenoid, and the d terminal is the negative pole of the power supply.

3. [2019•Beijing Daxing District]As shown in the picture, place a small magnetic needle at each end of the solenoid (the black end is the N pole), and sprinkle iron evenly on the cardboard crumbs. After energizing, you can observe the direction of the small magnetic needle. If you tap the cardboard gently, you can see that the iron filings are arranged regularly. Regarding the magnetic field of the energized solenoid, which of the following statements is correct (A)

A. These iron filings can be used to show the distribution of the magnetic field of an energized solenoid.

B． It can be determined from the direction of the small magnetic needle that the left end of the energized solenoid is the S pole.

C. The magnetic field around an energized solenoid is similar to the magnetic field around a shoe magnet

D. If the direction of the current in the energized solenoid is changed, the point of the small magnetic needle remains unchanged.

4. [2018•Guangxi Guigang]The distribution of magnetic field lines near the energized solenoid and magnet A is as shown in the figure. The small magnetic needle is at rest, then (　C　)

A. The b end of the small magnetic needle is the N pole

B． The left end of the energized solenoid is the N pole

C. The positive power supply is terminal C

D. The positive power supply is terminal d

Electromagnetic PPT, part 4: layered operations

1. [2018•Guiyang, Guizhou]As shown in the picture, it is part of the experimental device to explore "whether there is a magnetic field around a energized straight wire". There is a straight wire parallel to the small magnetic needle placed above the horizontal table. Regarding this experiment, which of the following statements is correct (C)

A. The scientist who first revealed the relationship between electricity and magnetism through this experiment was Faraday

B． When the straight wire is energized, the small magnetic needle will leave the bracket and levitate.

C. A small magnetic needle is used to test whether there is a magnetic field around a straight current-carrying wire.

D. Change the direction of current in a straight wire, and the direction of the N pole of the small magnetic needle remains unchanged.

2. [2018•Hunan Yiyang]As shown in the picture, place a small magnetic needle near the energized solenoid. After it is stationary, the small magnetic needle points to the correct direction (the black end represents the N pole of the small magnetic needle) (　C　)

3. [2019•Beijing Daxing District]According to the current direction marked in the picture, it can be judged that the B end of the electromagnet is the S (optional "N" or "S") pole.

4. [2018•Jiangsu Zhenjiang]As shown in the picture is a schematic diagram of the Oersted experiment. The experimental conclusion is that there is a magnetic field around the energized wire, and the phenomenon that supports this conclusion is the deflection of the small magnetic needle. If the small magnetic needle is removed, the magnetic field still exists (optional "still exists" or "does not exist").

5. [2018•Zhejiang Shaoxing] Thomson discovered electrons when studying cathode rays. As shown in the figure, a cathode ray emitted upward can be regarded as an electron flow formed by the directional movement of many electrons, then Inferring the direction of the current and surrounding magnetic field from the direction of movement of this electron flow is (　A　)

[Analysis] It can be seen from the figure that the direction of electron movement is upward. The electron is negatively charged, so the direction of the current is downward. According to Ampere's rule, it can be seen that the direction of the magnetic field is clockwise, so A is correct.

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Update Time: 2024-10-03

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