"Rheostats" Simple Circuit PPT Courseware 5

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"Rheostats" Simple Circuit PPT Courseware 5

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sliding rheostat

The structure consists of a porcelain cylinder, a coil wrapped around the porcelain cylinder, a metal rod above the porcelain cylinder, an insulating bracket, a metal slide that can slide freely on the metal rod, and four terminals.

Principle: Change the resistance by changing the _____ of the resistance line connected to the circuit

Connection method: one up and one down. Before connecting to the circuit, the resistance should be adjusted to the resistance value _____

Function (1) Change the resistance by changing the length of the resistance wire connected to the circuit, thereby gradually changing the current in the circuit, (2) _____ circuit

Advantages and disadvantages: Can _____ change the resistance value connected to the circuit, but cannot read the resistance value connected to the circuit

Resistance box

When reading the resistance value of the resistor box connected to the circuit, multiply the indication point (small triangle) corresponding to each dial by the multiple marked on the panel, and then add them together to get the resistance value of the resistor box connected to the circuit. Resistance

Advantages and Disadvantages You cannot _____ change the resistance value of the connected circuit, but you can read the resistance value of the connected circuit.

Connection of sliding rheostat and judgment of resistance change

As shown in the figure, the resistance wire with an insulating layer on the surface is tightly wound around the porcelain cylinder to form a coil, and its beginning and end are connected to two terminals A and B respectively. There is a metal rod CD above the porcelain cylinder connected to the bracket, and there is a terminal on the C end and D end. The slider P can slide left and right on the metal rod, and the insulation layer at the contact point between the coil and the slider has been scraped off. When the slider slides, the length of the connected resistance wire changes, causing the connected resistance to change accordingly. This is the principle of the sliding rheostat.

Since the sliding rheostat has many terminals and is connected to two terminals at the same time, it is easy to connect them incorrectly. When using them, you should pay attention to the following points: ① They should be connected in series in the circuit and adopt the "one up and down" wiring method; ② They cannot be used at the same time. The upper two terminals (R=0) cannot be used at the same time (R is a fixed value, that is, the maximum resistance). This will not achieve the purpose of changing the resistance in the circuit; ③ Understand the sliding rheostat used The resistance range and the maximum current value allowed to pass must not exceed the maximum allowable value; ④ In order to protect the circuit, the slider should be moved to the maximum resistance position before powering on, even if the resistance value connected to the rheostat is the maximum.

Changes in resistance must always be judged based on the specific wiring. The specific method is to first determine which part of the resistance wire is connected to the circuit, then look at the change in the length of that part when the slide moves in a certain direction, and finally determine the change in resistance based on the change in length, that is, as the length increases, the resistance becomes larger, and vice versa. . That is, relative to the "lower" terminal, the near is small and the far is large.

[Example] After two sliding varistors are connected to the circuit as shown in the figure, to minimize the current in the circuit, the positions of the sliders P1 and P2 should be ()

A.P1 and P2 are moved to the far left

B.P1 and P2 are moved to the far right

C.P1 moves to the far left and P2 moves to the far right

D.P1 moves to the far right and P2 moves to the far left

Analysis: It is easy to choose A incorrectly in this question, thinking that as long as the sliding blades of the two sliding varistors are slid to the far left, the resistance values ​​of the two sliding varistors will be the largest. The reason for the mistake is that the structure and working principle of the sliding varistor are not truly understood.

To minimize the current in the circuit, the resistance connected to the sliding rheostat should be the largest. In the question, the two sliding rheostat are connected in series and should be adjusted to the farthest position from the "lower binding post", so option D is correct.

1. Using a sliding rheostat to change resistance is achieved by changing which of the following factors ()

A. Material of resistance wire

B. Cross-sectional area of ​​resistance wire

C.Total length of resistance wire

D. The length of the resistance wire connected to the circuit

2. To dim the light bulb in the picture, slide the slider ()

A.Move to the right

B.Move to the left

C. Either left or right

D.Unable to judge

3. The volume control knob of the radio is a potentiometer, which is actually a ______. It changes the current by changing the size of ______, thereby changing the volume of the sound.

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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: 2024-11-25

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