"Rheostats" voltage resistance PPT teaching courseware

"Rheostats" voltage resistance PPT teaching courseware

Part One: Guidance Design

Learning Point 1 Rheostat

Question 1: What methods do you have to change the current in a circuit?

Answer: Change the _________ at both ends of the circuit or change the _________ in the circuit.

Question 2: We can change the resistance in the circuit by changing the _______, _______, and ________ of the conductor. Among these methods, you think the simplest and easiest method is to change the ________ of the conductor.

Experiment 1: Select a pencil lead and connect the circuit as shown in Figure 16-4-6. Move the clamp on the pencil lead and observe the brightness of the small bulb.

Thinking: Question 3: The shorter the length of the pencil lead connected to the circuit, the more ______ the resistance, and the more ______ the small light bulb is; the longer the length of the pencil lead connected to the circuit, the greater the ______ the resistance, and the ______ the small light bulb is.

Question 4: In order to increase the variation range of resistance in the access circuit, the ______ of the pencil lead can be increased.

Experiment 2: Observe the sliding rheostat shown in Figure 16-4-7.

think:

Question 5: There is _________ between the two terminals A and B. The resistance wire is coated with _________ and wound around the insulating tube.

Question 6: There is __________ between the two terminals C and D. The insulation layer of the resistance wire in contact with the slider P is scraped off, and the resistance wire can be connected to the slider P; when the slider moves to a different position, A The ___________ of the resistance wire between the two binding posts , C (or B, C) is different, so that the size of the resistance in the access circuit can be changed.

Question 7: As shown in Figure 16-4-8, the nameplate of the sliding varistor is marked with "1.5 A 200 Ω". 1.5 A refers to _________________________________________, and 200 Ω refers to _______________________________________________; in order to protect the circuit, before connecting the circuit The resistance should be adjusted to ____________.

Learning point 2: Use of sliding rheostat

The physical circuit diagram shown in Figure 16-4-9 is a circuit designed and connected by Xiaoli when she was exploring "how to use a sliding rheostat to change the brightness of a light bulb."

think:

Question 1: For a rheostat to control the brightness of a light bulb, the rheostat should be connected to the light bulb _______. There are 4 binding posts on the sliding rheostat. To connect these binding posts to the circuit, there are _______ ways to connect them.

Question 2: There are _______ connections that can change the size of the resistance in the access circuit. The effect of A and C being connected to the circuit is the same as that of ________ being connected to the circuit. The effect of B and C being connected to the circuit is the same as __________ being connected to the circuit. same.

Question 3: There are _______ connection methods that cannot change the resistance in the access circuit. ______The resistance between the two terminals is very small; ______The resistance between the two terminals is the maximum resistance marked on the nameplate. .

Learning point 3: Application of sliding rheostat

Figure 16-4-10 shows the appearance and structural diagram of the volume potentiometer of the radio.

Question: Connect terminals 1 and 2 to the circuit, and when the sliding contact rotates in the _____ clockwise direction, the volume becomes louder; connect terminals 2 and 3 to the circuit, and when the sliding contact rotates in the _____ clockwise direction, the volume becomes louder. The volume gets louder.

Rheostat PPT, Part 2: Application Examples

Type 1 Structure and Principle of Sliding Rheostat

Example 1 Regarding the sliding rheostat (shown in Figure 16-4-2), which of the following statements is correct ( )

A． The component symbol of the sliding rheostat can be expressed as "________"

B． The sliding rheostat changes the resistance by changing the cross-sectional area of ​​the resistance wire connected to the circuit.

C. The minimum resistance of the sliding rheostat is 20 Ω, and the maximum current allowed to pass through is 1 A.

D. The sliding plate and the resistance wire of the sliding varistor are conductive, and the porcelain cylinder and the resistance wire are insulated.

[ Analysis "A", "20 Ω" means that the maximum resistance of the sliding varistor is 20 Ω, "1 A" means that the maximum current allowed to pass through the sliding varistor is 1 A; there is conductivity between the sliding piece and the resistance wire, otherwise the resistance cannot be changed , the porcelain cylinder and the resistance wire are insulated.

Type 2 Use of sliding rheostat

Example 2 As shown in Figure 16-4-3, a sliding rheostat is connected to the circuit. The following statement about the use of sliding rheostat is incorrect ( )

A． If you want to use a sliding rheostat to change the brightness of a small bulb, you should connect the sliding rheostat in series with the small bulb.

B． If terminals B and D are connected, the slider P moves to the right, the resistance in the connected circuit decreases, and the bulb becomes brighter.

C. If the A and D terminals are connected, the slider P moves to the right, the resistance in the connected circuit decreases, and the bulb becomes dim.

D. If the A and B terminals are connected, the slider P moves to the right, the resistance value in the connected circuit remains unchanged, and the brightness of the small bulb remains unchanged.

[ Analysis When the piece P moves to the right, the length of the resistance wire in the circuit becomes shorter, the resistance becomes smaller, the current becomes larger, and the small bulb becomes brighter. The statement in option B is correct; if the A and D terminals are connected, the resistance wire AP is connected In the circuit, when the slider P moves to the right, the length of the resistance wire connected to the circuit becomes longer, the resistance increases, and the small bulb becomes dim. The statement in option C is incorrect; if the A and B terminals are connected, the resistance of the sliding rheostat will All the wires are connected to the circuit, the slider P moves to the right, the resistance in the circuit remains unchanged, and the brightness of the small bulb remains unchanged. Option D is correct.

[ Method guidance Go big and far.

Type 3 Application of Rheostat

Example 3 A classmate designed a wind force measuring instrument, as shown in Figure 16-4-4. O is the rotation axis, OC is the metal rod, and a wind receiving plate is connected below. When there is no wind, OC is vertical. The stronger it is, the greater the deflection angle of the OC rod; AB is an arc-shaped resistor, and point P is the point where the metal rod contacts the arc-shaped resistor; there is a light bulb L in the circuit. When measuring the wind force, close the switch S. Through analysis, it can be seen that the combination of metal rod OC and arc resistor AB is equivalent to a _______________. Observing the brightness of light bulb L can roughly reflect the size of the wind; if you want to improve the performance of the device in reflecting the size of the wind, the method that can be adopted is_ _______________.

[ Analysis To improve the performance of the device in reflecting the wind force, an ammeter can be connected in series in the circuit to reflect the wind force through the current. The greater the current, the greater the wind.

[Method guidance]Problem solving skills related to rheostat application

In a circuit, the main function of a rheostat is to change the current in the circuit by adjusting its resistance value. Therefore, the most important thing in solving this kind of question is to clarify the changes in the resistance of the varistor, and then judge the changes in the current in the circuit. Under normal circumstances, changes in current will be expressed through the brightness of the light bulb or the indication of the ammeter (it can also be some other easily observed phenomena). Common applications of rheostat include: ① The potentiometer for adjusting the volume on the radio; ② The speed control handle of an electric bicycle. Its function is to adjust the rotation speed of the electric bicycle to control the speed of the electric bicycle.

Rheostat PPT, Part 3: Class Feedback

1. The sliding rheostat changes the resistance by changing the resistance wire ________ connected to the circuit. The correct connection must comply with the principle of "________". If the two terminals above are connected at the same time, it is equivalent to connecting a section of _ _______, if the two terminals below are connected at the same time, the sliding rheostat at this time is equivalent to a ____________.

2. The nameplate of a sliding rheostat is marked with "50 Ω 2 A", where "50 Ω" means: ____________________________________________________________; "2 A" means: ____________________________________________.

3. Figure 15-1 shows several connection methods of sliding rheostat. Among them, the one that can play the role of rheostat is ________; the one that cannot play the role of rheostat is ________. When the slider moves to the right, the resistance becomes larger as ________, and the resistance becomes smaller as ________. Among these connection methods, the one with the same effect when the slide moves is ________. When connected to the circuit as shown in Figure A, the slider should slide to the ________ end.

4. As shown in Figure 15-2, it is a rotating disk resistance box. At this time, the resistance value between the terminals of the resistance box is ________Ω.

5. The potentiometer shown in Figure 15-3 is essentially a kind of ____________, which changes the resistance value by changing the ____________ of the resistance wire connected to the circuit.

6． As shown in Figure 15-4, when the slider P of the varistor moves to the right, the bulb becomes brighter. Please add a wire in the picture to complete the circuit connection.

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For more information about the "Voltage Resistor Rheostat" PPT courseware, please click on the Voltage Resistance ppt Rheostat ppt tag.

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