"End of Chapter Summary and Improvement" Current and Circuit PPT

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"End of Chapter Summary and Improvement" Current and Circuit PPT

Part One: Key Breakthroughs

Type 1 Two Charges

1. (Zhangjiajie High School Entrance Examination) In autumn, a plastic comb used on dry hair will pick up scraps of paper. This is a phenomenon of frictional electrification; when the comb is close to the negatively charged balls, the balls are repelled, indicating that the comb is negatively charged. .

2. Two dry insulators A and B are separated after rubbing against each other. Since the nucleus of A has a strong binding ability to electrons outside the nucleus, electrons are obtained after friction. The following statement is correct (B)

A. B is negatively charged B. A and B will attract each other when they are close

C. A is positively charged D. A and B will repel each other when they are close

3. (Mianyang High School Entrance Examination) There are three light balls A, B, and C. It is known that A is positively charged, A and B repel each other, and A and C attract each other, then (B)

A. B is positively charged, and C must be positively charged.

B. B is positively charged, but C may not be charged.

C. B is negatively charged, and C must be negatively charged.

D. B is negatively charged, and C may be negatively charged.

Type 2 Series and parallel circuits

4. (Jiangxi High School Entrance Examination) On the highway, the street lights are connected in parallel; when you return home, press the switch and the light turns on, and the switch and the light are connected in series.

5. Xiao Ming discovered that when a switch in the classroom is turned on, four lights turn on at the same time, and when the switch is turned off, four lights turn off at the same time. Then these lights are (C)

A. Series B. Parallel

C. Both series and parallel connections are possible D. Undetermined

6. The picture shows a certain brand of juicer. To ensure safety, the juicer is equipped with double switches - power switch S1 and safety switch S2. When the cup body is placed upside down on the main unit, S2 automatically closes. At this time, S1 is closed again before the motor can start and start juice extraction. Which of the following circuit diagrams meets the above requirements is (C)

7. A classmate observed an electric bicycle and found that: when the left or right brake is tightened, the brake indicator light at the rear of the vehicle will light up; when the steering switch to the left or right is flipped, the rear of the vehicle only turns to the corresponding side. The indicator light will light up. The following schematic diagram of the indicator light is reasonable (D)

Type 3: The law of current in series and parallel circuits

8. When two small bulbs L1 and L2 of different types are connected in parallel, the current ratio passing through them is 2:3. If the lamps L1, L2 and another small bulb L3 form a series circuit, the current ratio passing through L1 and L2 is 1:1.

9. As shown in the figure, when the switch S1 is turned off and S2 and B are turned on, the ammeter indicates 0.15 A, then the current through the lamp L1 is 0.15 A, and the current through the lamp L2 is 0.15 A; when the switch When S1 is connected and S2 is connected to A, the ammeter's indication is 0.8 A, and the current it measures is the main circuit current.

10. In the experiment of "measuring current with an ammeter", a student designed the circuit as shown in Figure a. When the switches are closed, both lamps glow, and the pointers of the two ammeters point to the positions shown in Figure b, then the current through lamp L2 is 0.32 A; if S2 is open, the current through lamp L1 is 1.28 A, and the ammeter The indication of A1 becomes smaller (choose "get bigger", "no change" or "get smaller").

End-of-Chapter Summary and Improvement PPT, Part 2: Experimental Activities

Experiment: Explore the current laws of series and parallel circuits

1. Experimental equipment: light bulbs, switches, power supplies, wires, and ammeters.

2. Experimental circuit

3. Experimental process: Use an ammeter to measure the currents at A, B, and C in Figures A and B respectively, and record the data; change light bulbs of different specifications for multiple measurements; finally observe and analyze the data, and draw conclusions.

4.Experimental conclusion

(1) The currents everywhere in the series circuit are equal;

(2) The trunk current in a parallel circuit is equal to the sum of the branch currents.

[For training]

1. Xiaohu explores the "laws of current in series circuits" according to the circuit as shown in the figure:

(1) After connecting the circuit, close the switch. Xiaohu found that both bulbs L1 and L2 did not light up. He pressed bulb L1 with his hand. L1 and L2 still did not light up. He pressed bulb L2 and both lights lit up. Release it. If the two lights do not light up, the fault may be poor contact of L2 (optional "L1 filament is broken", "L2 filament is broken" or "L2 is in poor contact");

(2) After troubleshooting, connect the ammeter to different locations such as A, B, C, etc., observe and record the current indication, and you can initially draw the conclusion: the current everywhere in the series circuit is equal;

(3) In order to make the conclusion more general, Xiaohu’s next operation should be to use small light bulbs of different specifications to conduct multiple experiments.

2. When exploring the relationship between the main circuit current and the branch current in a parallel circuit, each group of students in a class randomly selected two bulbs of four specifications A, B, C, and D and connected them in parallel to the same power supply. above, forming the circuit shown in Figure 1. Then connect an ammeter to the circuit at A, B, and C to measure the current and record the data.

(1) If you want to measure the main circuit current, the ammeter should be connected in series at C (optional "A", "B" or "C") in Figure 1;

(2) Xiao Li connects the ammeter to point A, closes the switch, and the current indication is as shown in Figure 2. In order to obtain accurate measurement results, she should turn off the switch, switch to the small range of the ammeter, and conduct the experiment again;

End-of-Chapter Summary and Improvement PPT, Part Three: Connection between Junior High School and High School

1. Electric field: There is an electric field around the charge. The characteristic of the electric field is a powerful effect on the charge placed in it. The direction of the electric field at a certain point can be defined as the direction of the force exerted by the positive charge at that point.

2. Current intensity and charge amount: The amount of charge passing through the cross-sectional area of ​​the conductor per unit time is called current intensity. Define the formula I=Q/t, Q represents the amount of charge, and the unit is library (C); the microscopic expression of the current in a metal conductor is I=neSv, n is the number of free electrons per unit volume, e is the charge of the electron, and S is the conductor Cross-sectional area, v is the charge velocity.

[For training]

1. Static electricity has important applications in various industries and daily life, such as electrostatic dust removal, electrostatic copying, etc. The basic principles are almost all based on making charged material particles rush towards and adsorb to electrodes under the action of electric field. There are three particles a, b, and c shot downward from point P into the electric field generated by the positive and negative electrodes. Their motion trajectories are as shown in the figure, then (B)

A.a has a negative charge, b has a positive charge, and c has no charge.

B.a has a positive charge, b has no charge, and c has a negative charge.

C.a has a negative charge, b has no charge, and c has a positive charge.

D.a has a positive charge, b has a negative charge, and c has no charge.

2. Regarding current, which of the following statements is correct (D)

A. According to I=Q/t, it can be seen that I is proportional to Q

B. The more free charges in a conductor, the greater the current

C. The larger the cross-sectional area of ​​the conductor, the larger the current

D. The unit of current, "ampere", is the basic unit in the International System of Units.

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Update Time: 2024-07-10

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