"Rheostats" Voltage Resistance PPT Courseware 4

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"Rheostats" Voltage Resistance PPT Courseware 4

review:

Factors that determine resistor size

For conductors of the same material and cross-sectional area, the greater the length, the resistance ______.

For conductors of the same material and length, the larger the cross-sectional area, the greater the resistance______.

For conductors with the same length and cross-sectional area, the resistance depends on the material.

Experiment summary

Phenomenon:

When the length of the pencil lead connected to the circuit becomes longer, the current represents the number ______ and the brightness of the light bulb is ______.

When the length of the pencil lead connected to the circuit becomes shorter, the current represents the number ______ and the brightness of the bulb is ______.

Inspiration:

Changing the ______ of the resistor wire connected to the circuit can change the ______ of the connected circuit, thus changing the ______ of the circuit.

1. Rheostat

Principle and function:

By changing ____________, the resistance connected to the circuit is changed, thereby changing the ______ in the circuit.

2. Structure of varistor

1. Physical object and name

①Metal rod ②Metal slide P ③Resistance wire ④Porcelain cylinder ⑤Bracket

2. Structural diagram and symbols

3. The words "2A, 20Ω" marked on the sliding rheostat. "2A" means that the maximum current value allowed to pass is 2A, and "20Ω" means that the maximum resistance of the rheostat is 20 ohms.

4. Application of sliding rheostat:

The potentiometer used to adjust the volume of radios and televisions is a rheostat.

Changing the resistance changes the current

Rotating disk resistance box

The difference and connection between resistance box and sliding rheostat.

Connection: can change the resistance value connected to the circuit;

Difference: The sliding rheostat can gradually change the resistance connected to the circuit, but it cannot accurately read the resistance value connected to the circuit; the resistance box is just the opposite.

Book P68-69 Exploration Experiment

1. Where on the resistance wire has the insulating paint been scratched off? Why scrape it off?

2. The resistance between which two terminals is constant?

3. The resistance between which two terminals is very small, almost zero?

4. When the slider is moved, the resistance between which two terminals changes? In which direction does the resistance increase as you move?

feedback exercise

1. As shown in the figure, two sliding varistors are connected in series and then connected to the circuit. To minimize the current in the circuit, the positions of sliders P1 and P2 should be placed ( )

A. P1 is at the far right and P2 is at the far left

B． P1 is at the far left and P2 is at the far right

C. P1 is at the far left, P2 is at the far left

D. P1 is at the far right, P2 is at the far right

2. It is required to use the sliding rheostat to only change the brightness of the bulb L1, and when the sliding rheostat moves to the right, the lamp L1 becomes brighter; the ammeter measures the current of the bulb L2.

(1) Draw the circuit diagram.

(2) Answer based on the circuit diagram you drew: When the slide p moves to the left, how does the resistance connected to the rheostat change? How does the brightness of the small light bulb change? How does the current representation change?

Practice in class

1. A sliding rheostat is a device that changes resistance by changing the ______ in the circuit.

2. Connect the two terminals on the metal rod of the sliding rheostat to the circuit and move the slide of the sliding rheostat. The change in the current indication number is _____, which indicates the problem is _____.

Connect the two terminals on the coil to the circuit and move the sliding rheostat slide. The change in the ammeter's indication is ____, indicating that the problem is ____.

3. Which of the following statements is correct ( )

A. Sliding rheostat is better than resistor box

B. Two copper wires with different thicknesses, the thinner one has greater resistance

C. The resistance box can gradually change the resistance connected to the circuit

D. Before connecting the circuit and closing the switch, the resistance of the sliding rheostat connected to the circuit should be maximized.

summary

The structure and principle of sliding rheostat:

How to use sliding rheostat

Only use "one up and one down"

Only with the correct connection method can the sliding rheostat play the role of changing resistance.

The change in resistance is determined by the change in the distance between the slider and the wired lower terminal (that is, the length of the resistance wire connected to the circuit): the farther the slider is from the wired lower terminal, the greater the resistance; the closer the distance. , the smaller the resistance.

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

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"Rheostats" PPT courseware:

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Update Time: 2024-09-17

This template belongs to Physics courseware People's Education Edition Ninth Grade Physics Complete Book industry PPT template

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