"DC Motor" Magnetic Phenomenon PPT Courseware 3

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"DC Motor" Magnetic Phenomenon PPT Courseware 3

Experience the principles of DC motors

Activities: Prepare two batteries, a piece of enameled wire, a magnet, and a wire stand.

Activity 1: As shown in the picture, wind the enameled wire into a rectangular coil.

Scrape off all the paint layers on both ends of the enameled wire, as shown in the figure

Connect the circuit and observe the rotation of the coil.

Activity 2: Scrape off all the paint layer on one end of the enameled wire.

Only scrape off half of the paint layer on the other end, connect the circuit, and observe the rotation of the coil.

(1) In activities 1 and 2, the coil _________ (optional "can" or "cannot") rotates because of __________________.

(2) In activity 1, the coil ________(please fill in "can" or "cannot") continues to rotate. In activity 2, the coil ___________ (optional "can" or "cannot") continues to rotate.

Tips: (1) Energy A current-carrying conductor is acted upon by a force in a magnetic field

(2)cannot be able

pre-study questions

1. What is the working principle of electric motor?

2. What is the equilibrium position?

3. What is the function of commutator?

4. What are the structures of electric motors?

5. In what aspects are electric motors used in life?

Explore the principles of DC motors

Consider the following questions based on “experience” and the picture below:

1. In the "experience" activity, why can the coil rotate after the circuit is connected?

Tip: After the circuit is turned on, there is current flowing through the coil, and the current direction in the enameled wires on the upper and lower sides is opposite. The energized coil is acted upon by the magnetic field force in the magnetic field, and the magnetic field force on the two sides is opposite in direction, so the coil starts to rotate.

Reference answer: The energized coil is affected by the magnetic field force in the magnetic field.

2. Connect the circuit according to Figures A and B. When the energized coil rotates through _____ degrees, the force is balanced. Analyze the force situation when the coil is stationary. Why does the coil not rotate continuously?

Tip: The directions of the forces on the upper and lower sides of the energized coil in the magnetic field are different. When these two forces act on a straight line, the position of the coil is called the equilibrium position. When the coil reaches the equilibrium position, it will rush through due to inertia. Equilibrium position, swing back and forth several times near the equilibrium position and then stop moving.

Reference answer: 90 The forces on the upper and lower sides of the coil in the equilibrium position are equal in magnitude and opposite in direction, acting on a straight line.

3. Analyze Figures A and B. What changes have occurred in the direction of the current in the coil? Why can the coil continue to rotate a little when it is moved to the position in Figure B?

Tip: In Figure A, commutator F is in contact with brush A, commutator E is in contact with brush B, the current in side ab of the coil is from b to a, and is subject to the upward magnetic field force, and the current in side cd is from d Toward c, it is subjected to a downward magnetic field force, so the coil begins to rotate in a clockwise direction; Figure B is the equilibrium position. At this time, there is no current in the coil, and the coil is not affected by the magnetic field force. The coil will rush past this position due to its inertia.

Reference answer: In Figure A, the current in side ab of the coil flows from b to a, and in side cd, the current flows from d to c. There is no current in the coil in figure B. There is no current in figure B. The coil is not affected by force, and it rushes through the equilibrium due to its inertia. position so that it can continue to rotate a little bit.

Knowledge summary

1. Principle of DC motor

1. Balance position:

During the rotation of the coil, the direction of force on the two sides is _____, and the position on ___________.

2. Exercise situation:

The energized coil rotates _______ in the magnetic field. When it reaches the equilibrium position, it can rush past the equilibrium position due to _____.

3. Commutator and brushes:

(1) Structure:

① Commutator: It consists of two semicircular _________.

② Brush: It consists of two elastic metal sheets, one end is connected to a wire, and the other end is close to _______.

(2) Function: Whenever the coil just rotates through ________, the commutator, with the cooperation of _____, can automatically change the _________ in the coil, so that the coil continues to rotate.

2. Practical electric motors

1. Structure: Mainly composed of _____ and _____.

2. Principle: It is made by using ______________ to rotate.

3. Energy conversion: Convert _____ into _______.

4.Type:

(1) DC motor: powered by _____ power supply. For example, cranes, electric toys, tape recorders, DVD players, etc.

(2) AC motor: powered by _____ power supply. For example, fans, washing machines, refrigerators, etc.

Test Points Working Principle of DC Motor

[Typical example] Figure A is a DC motor model, and Figure B is a self-made simple motor model. Now we mainly discuss the production and operation of the simple motor in Figure B:

(1) The copper wire used to wind the coil has paint on the surface. The two ends of the coil lead-out wire (the part resting on the copper hook) must be scraped with paint. The scraping method is shown in the enlarged picture. The purpose of scraping paint in this way is to make the coil ______, so this part is equivalent to _______ in Figure A (fill in the name of a certain part).

(2) If there is no problem with the entire production, but the coil does not move after the power is connected, what should you try? (Just mention two points)

①_______________________________;

②_______________________________.

[Concise Lecture and Analysis] This question examines the working principle of a DC motor.

(1) Scrape the paint on both ends of the coil lead wire (the part resting on the copper hook). This is equivalent to adding two commutators, and the coil can rotate continuously;

(2) The reason why the coil does not move may be that the coil just stops at the equilibrium position, the magnetic field force received by the coil is small, etc. Therefore, if the coil moves to the equilibrium position and does not move, you can give it a force with your hand to make it cross the equilibrium. The position continues to rotate; if it is not at the equilibrium position, it means that the magnetic field force received is small. You can enhance the magnetism and increase the number of batteries to increase the current in the coil, so that the magnetic field force received by the coil increases.

1. Which of the following devices is made based on the experimental principle shown in the figure ( )

A. Electric iron B. Electric motor

C.Electromagnet D.Generator

[Analysis] Choose B. This question examines the principles of electric motors. What is explored in the picture of this question is the force movement of the energized conductor in the magnetic field. This is the principle of the electric motor, so option B is correct; the principle of the electric iron is the thermal effect of the current, the principle of the electromagnet is the magnetic effect of the current, and the principle of the generator is Electromagnetic induction, so options A, C, and D are all wrong.

2. Among the four experimental phenomena shown in the figure, the one that reveals the principle of the electric motor is ( )

[Analysis] Choose B. This question examines the principles of electric motors. Experiment A is the experimental device of Oersted's experiment; Experiment B is an experimental device that studies the forced motion of a energized conductor in a magnetic field, and is also the schematic diagram of an electric motor; Experiment C is an experimental device that explores the law of interaction between charges; Experiment D is a research Experimental setup for electromagnet magnetism.

3. As shown in the figure is the model of a DC motor. After closing the switch, the coil rotates clockwise. Now you want the coil to rotate counterclockwise. The following methods are feasible: ( )

A. Only change the direction of current

B. Only change the current size

C. Change to a stronger magnet

D. Swap the magnetic poles and change the direction of the current at the same time

[Analysis] Choose A. This question examines the factors that influence the direction of force on a current-carrying conductor in a magnetic field. The direction of the force exerted by an energized conductor in a magnetic field is related to the direction of the current and the direction of the magnetic field. If only one of the factors is changed, the direction of the force exerted on the conductor will change. If both factors are changed at the same time, the direction of the force exerted on the conductor will not change. Therefore, A is correct and D is incorrect. ; The two factors B and C will only change the force on the conductor.

Find out where you tend to go wrong?

Electric motors are made using the principle of __________. As shown in the picture, in the experiment of "making the coil rotate", in order to make the coil continue to rotate, the method adopted is to _________ the patent leather of the leads at both ends of the coil; to make the coil rotate in the opposite direction to the original, use_ _________ or __________ method.

[Students’ own answers]

①Magnetic effect of current ②Scrape it all off Change the direction of the current Change the direction of the magnetic field

[Teacher Comments]

① Wrong understanding of the principle of the electric motor: it should be that the energized coil is acted upon by force in the magnetic field;

② Operation error: If both ends are scraped off, the coil will stop when it reaches the equilibrium position and cannot

Keep turning.

【Correct solution】

The energized coil is forced to rotate in the magnetic field

Scrape off all of one end and only half of the other end.

Change the direction of current Change the direction of magnetic field

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Update Time: 2024-10-06

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