Guangdong and Shanghai Edition Ninth Grade Physics Volume 1

Description

"Exploring Current in Series and Parallel Circuits" Exploring Simple Circuit PPT Courseware

learning target

1. Ability to use ammeters to measure current in series and parallel circuits.

2. Know the current characteristics of series and parallel circuits.

3． Understand the basic methods of quantitatively studying physical problems - measuring data, analyzing and summarizing, and drawing conclusions.

Core test point: The laws of current in series and parallel circuits.

Preview before class

1. The currents in the series circuit ________ are equal, and the currents in the trunk circuit in the parallel circuit are equal to .

2. There are 20 small light bulbs connected in series on a holiday lantern. If the current at the power plug is 150 mA, then the current through the tenth light bulb is ()

A.0.15 A B.1.5 A C.7.5 mA D.3A

3． In order to measure the current through bulb L1 in the circuit diagram, where in the figure below should the ammeter be connected ( )

A. Only at point A B. Only at point B

C. Only at point C D. All three points A, B, and C are fine.

Lectures in class

Knowledge point 1. Current laws of series circuits

The current is equal everywhere in a series circuit, that is.

[Typical Example 1] (2014·Longyan) Lamps L1 and L2 are connected in series in a circuit. It is found that lamp L2 is much brighter than lamp L1. Which of the following statements is correct ( )

A. The current through L2 is greater than L1

B． The current through L2 is smaller than L1

C. The current through both lamps is the same

D. It is impossible to compare the current flowing through the two lamps

[Exercise 1] The series circuit shown in the figure below, when the switch is closed ( )

A. The current passing through point A is greater than the current passing through point B.

B. The current passing through point B is greater than the current flowing through point C.

C. The current passing through point A is greater than the current flowing through point C.

D. The currents passing through three points A, B, and C are equal

Knowledge point 2. Current law of parallel circuits

In a parallel circuit, the current in the main circuit is equal to the sum of the currents in each branch. That is: I=I1+I2+…=In, where I represents the current in the trunk circuit, I1, I2…, and In represents the current in each branch. (Note: The currents in each branch of a parallel circuit are not necessarily the same. The trunk current in a parallel circuit is larger than the current in any branch)

[Typical Example 2] (2014·Huaihua) In the circuit as shown in the figure, after closing the switch, compare the currents at a, b, c, and d. The correct one is ( )

A. Ia=Id B. IaIc D. Ic=Id

[Exercise 2] Three identical lamps L1, L2, and L3 form the circuit as shown in the figure below. The indications of the ammeters A1, A2, and A3 are I1, I2, and I3 respectively. Their relationship is ( )

Knowledge point 3. Experimental study of current laws in series and parallel circuits

The characteristics of current in series and parallel circuits are basic knowledge of electricity. When studying, you must do the two exploratory experiments in the textbook, gain perceptual knowledge through the experiments, and then rise to rational understanding through analysis and induction, master the rules, form abilities, and scientific inquiry The general steps of the method: raise questions - conjectures and hypotheses - design experiments - conduct experiments - analyze arguments - evaluate.

When conducting experimental research, you should pay attention to the following two points:

(1) Before connecting the circuit, draw the circuit diagram. The switch should be in the off state. Check and confirm that it is correct before closing the switch for experiment;

(2) Whether you are exploring the current rules in a series circuit or a parallel circuit, the specifications of the light bulbs used cannot be the same, and multiple measurements are required to reduce errors and prevent accidental conclusions.

[Example 3] As shown in Figure 4, when exploring the current relationship in a parallel circuit, Xiao Ming used an ammeter to measure the currents at A, B, and C as IA=0.5A, IB=0.3A, and IC=0.2 A. After recording the data in the table, the first thing you should do next is ( )

A. Arrange the equipment and end the experiment

B． Use small light bulbs of different specifications and measure several sets of current values.

C. Analyze data and draw conclusions

D. Switch to another range of the ammeter and measure another set of current values.

In-class testing

1. When a student was exploring the current pattern of a series circuit, he connected the circuit as shown in Figure A. After closing switch S1, he observed the deflection of the two ammeters as shown in Figures B and C. Which of the following statements is correct ( )

A. The reading of ammeter A1 is smaller than the reading of ammeter A2.

B． Every time current flows through an electrical appliance, the circuit current will weaken a little.

C. The brightness of two light bulbs connected in series must be equal

D. The current in a series circuit is equal everywhere

2. In the circuit as shown in the figure, when the switch is closed, the reading of ammeter A is 0.6A and the reading of ammeter B is 0.2A. Then the following judgment is correct ( )

A. The current through lamp L1 is 0.6A

B． The current through lamp L1 is 0.4A

C. The total current through the circuit is 0.8 A

D. The current through lamp L2 is 0.4 A

3. As shown in the figure, the currents passing through lamps L1, L2, and L3 are 0.1A, 0.2A, and 0.3A respectively. Then the reading of ammeter A1 is _____A, and the reading of A2 is _____A.

4. As shown in Figure 1, the circuit was not connected when Xiao Ming and Xiao Qiang were doing the experiment of "Exploring the Current Laws of Parallel Circuits". Now the lamps L1 and L2 are required to be connected in parallel, and the ammeter measures the current in the lamp L2.

(1) Please use strokes to represent wires and help them complete the circuit connections to meet the requirements.

(2) Connect the circuit correctly as required, close the switch, and the ammeter indicates as shown in Figure 2A, then the current in lamp L2 is _____A.

(3) In this circuit, when an ammeter is used to measure the current in the main circuit, the ammeter’s indication is as shown in Figure 2B. Then the main circuit current is _____A, then the current in lamp L1 is _____A.

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For more information about the PPT courseware "Exploring Simple Circuits and Currents in Series and Parallel Circuits", please click the Explore Simple Circuits ppt and Explore Currents in Series and Parallel Circuits ppt tags.

"Exploring Current in Series and Parallel Circuits" Exploring Simple Circuits PPT Courseware 2:

"Exploring Current in Series and Parallel Circuits" Exploring Simple Circuit PPT Courseware 2 Teaching Objectives: 1. Be able to use ammeters to measure series and parallel currents and train basic skills in connecting circuits. 2. Understand the current characteristics of series and parallel circuits. 3. Be able to measure data, analyze and summarize, and draw conclusions..

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Update Time: 2024-11-22

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