"Rheostats" Simple Circuit PPT Courseware 3

Description

"Rheostats" Simple Circuit PPT Courseware 3

Basic combing and knowledge highlights

1. Structure: as shown in the figure

2. Principle: Change the size of the resistance by changing the length of the resistance wire connected to the circuit.

3. Structural diagram:

4. Circuit symbols:

5. How to use

(1) The sliding rheostat must be in the circuit with the electrical appliance to be controlled.

(2) When connecting the sliding rheostat to the circuit, the two terminals of ________ should be connected.

(3) Before closing the switch, the resistance of the sliding rheostat should be adjusted to _______.

Summary of key points and thought-provoking exploration

1. Experimental research: Using a sliding rheostat to change the brightness of a light bulb

1. Experimental equipment: sliding rheostat, small light bulb, battery pack, wires, switch.

2. Circuit diagram:

3. Experimental steps:

(1) Place the sliding piece of the varistor at the end where the varistor is connected to the largest resistance.

(2) Connect the physical objects according to the circuit diagram.

(3) Check that the circuit is correct and close the switch.

(4) Slowly slide the slider of the rheostat to gradually reduce the resistance and observe the brightness change of the bulb.

4. Phenomenon: The brightness of the small light bulb gradually becomes stronger.

5. Experimental conclusion: The resistance wire connected to the circuit of the sliding rheostat becomes shorter, the resistance connected to the circuit becomes smaller, and the light bulb becomes brighter.

Question exploration

1. What is the purpose of adjusting the sliding rheostat to the maximum value before closing the switch?

Tip: Protect the circuit.

2. Why can’t the sliding rheostat use the two upper terminals at the same time?

Tip: The resistance value is zero at this time, and it has no effect on changing the resistance.

3. Why can’t the sliding rheostat use the two lower terminals at the same time?

Tip: At this time it becomes a fixed value resistor, the resistance value is equal to the maximum value, and it cannot change the resistance.

4. If the sliding rheostat is connected in parallel with the light bulb in the circuit, can it change the brightness of the light bulb?

Tip: No. Because the branches of the parallel circuit do not affect each other.

5. Correctly connect the sliding rheostat in series to the circuit. When the slider is moved, how to accurately judge the change of the resistance connected to the circuit?

Tip: When moving the slider, look at the distance between the slider and the wiring post below. If the two are closer (the distance becomes smaller), the connected resistance will become smaller, otherwise the connected resistance will become larger.

2. Use of sliding rheostat

1. The resistance changes of different wiring groups of the varistor, as shown in the figure:

2. The sliding rheostat must be connected in series in the circuit, and the current passing through the sliding rheostat cannot exceed the current value marked on its nameplate.

Tips for using sliding rheostat: Correct connection method, one up and one down; two ups will cause a short circuit, two downs will have no change. Whether the resistance becomes larger or not, just look at the "sliding down": the resistance is small when moving closer, and the resistance is large when moving away.

[Typical example] In the circuit as shown in the figure, a sliding rheostat is used to adjust the brightness of the lamp. If the lamp is required to gradually dim when the slide P slides to the right end, then the following connection method is correct:

A, M is connected to C, N is connected to B B, M is connected to A, N is connected to B

C, M connects to C, N connects to D D, M connects to A, N connects to D

[Analysis] Choose A. This question tests the correct connection method of sliding rheostat. The sliding rheostat changes the resistance by changing the length of the resistance wire connected to the circuit. Its effective part is the part connected to the circuit. When connecting, the wiring should be "one up and one down". When judging, you should look at the binding posts. "Far, big, near, small", if the slider is far away from the lower terminal, the resistance in the connected circuit becomes larger, and vice versa. M is connected to C, N is connected to B, and when the slider P slides to the right, the PC segment becomes longer, so the resistance connected to the circuit becomes larger, and the light gradually dims. A is correct; when M is connected to A, and N is connected to B, the connection What is connected to the circuit is a metal rod, and the resistance value connected to the circuit is zero. No matter how the slider is moved, the brightness of the bulb remains unchanged. B is wrong; when M is connected to C and N is connected to D, the entire resistance wire is connected to the circuit. The resistance connected to the circuit is the largest, which is equivalent to a fixed-value resistor. No matter how the slider is moved, the brightness of the bulb remains unchanged. C is wrong; M is connected to A, N is connected to D, and when the slider P slides to the right, the PD segment becomes shorter. , so the resistance connected to the circuit becomes smaller, the light gradually becomes brighter, and D is wrong. Therefore choose A.

Error-prone analysis, drawing inferences from one instance

I don’t understand the principle of changing the resistance of a sliding rheostat

[Typical example] As shown in the figure, it is a device that automatically measures the amount of oil in the fuel tank. R is a sliding rheostat, and its metal slide P is one end of the lever. The pointer of the fuel gauge (modified from an ammeter) is By pointing to the scale, you can know the amount of fuel in the tank, then

A. As the oil volume increases, R increases, and the deflection of the fuel gauge pointer becomes smaller.

B. The amount of oil increases, R decreases, and the deflection of the fuel gauge pointer increases.

C. The amount of oil decreases, R increases, and the deflection of the fuel gauge pointer increases.

D. The amount of oil decreases, R decreases, and the deflection of the fuel gauge pointer decreases.

[Easy answers] A, C, D

Class training, basic standards

1. As shown in the figure, AB is the pencil lead. When the wire P end slides from B to A, regarding the brightness of the small bulb, which of the following statements is correct ( )

A. The small light bulb becomes brighter B. small light bulb dims

C. The brightness of the small light bulb remains unchanged D. Unable to judge

[Analysis] Choose A. When the P end of the wire slides from B to A, the part of the pencil lead connected to the circuit becomes shorter, that is, the resistance becomes smaller, the current becomes larger, and the bulb becomes brighter.

2. As shown in the figure, the sliding rheostat has 4 binding posts. Only two of them need to be connected when using it. Therefore, there are 6 connection methods. Among these connection methods, the resistance size cannot be changed and the connection method that may damage the instrument is ( )

A. Connect A and D B. Connect B and C

C. Connect A and B D. Connect C and D

[Analysis] Choose A. This question tests the correct connection method of sliding rheostat. To change the resistance in the circuit, the sliding rheostat must be able to change the length of the resistance wire connected to the circuit. Therefore, the correct wiring method is to choose two terminals "one up and one down". Options C and D do not meet the requirements of the question; choose When the two terminals B and C of the resistance wire are used, the resistance is unchanged and maximum, but it can protect the circuit. B does not meet the requirements of the question; when the two terminals A and D on the metal pole are selected, the resistance is unchanged and Minimum (0), the current in the circuit is the largest, which does not protect the circuit and may damage the instrument. Therefore choose A.

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For more information about the "Simple Circuit Rheostat" PPT courseware, please click on the Simple Circuit ppt Rheostat ppt tab.

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Update Time: 2024-10-02

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