"Resistors and Rheostats" Exploring Circuit PPT Courseware 3

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"Resistors and Rheostats" Exploring Circuit PPT Courseware 3

New course introduction

Why do wires need to be made of aluminum or copper?

Iron is also a conductor, so why not make it from iron which is both plentiful and cheap?

Demo 1

Connect copper wires and nickel-chromium alloy wires of the same length and thickness to the circuit respectively, close the switch, and observe the brightness of the small bulb in the circuit.

Experimental phenomena

By connecting different conductors, the brightness of the small bulb changes.

(1) Why do different metal wires have different currents under the same voltage?

Although conductors easily conduct electricity, they also hinder current flow. Under the same voltage, the current passing through the copper wire is larger, indicating that the copper wire has a smaller obstruction effect on the current; the current passing through the nickel-chromium alloy wire is smaller, indicating that the nickel-chromium alloy wire has a greater obstruction effect on the current.

1. Resistance

1. In physics, resistance is used to represent the resistance of a conductor to current flow.

The greater the resistance of a conductor, the greater its resistance to current flow. The resistance of a conductor is usually represented by the letter R.

2. Unit: ohm (ohm), referred to as ohm, symbol Ω.

3. The units of resistance are also: megaohm (MΩ) kiloohm (kΩ)

The conversion relationship is:

1 kΩ = 1 000 Ω = 103 Ω

1 MΩ = 1 000 000 Ω = 106 Ω

4. Resistor

In electronic technology, we often use components with a certain resistance value - resistors, also called fixed-value resistors, or resistors for short. It is represented by the symbol _______ in the circuit diagram.

2. Explore the factors that affect the resistance size

We see that the wires used for high-voltage power transmission use thick and straight metal wires. Why not use thin wires to transmit electricity?

Why not use thick and straight wires for the electric furnace wires on the electric furnace?

What other factors are related to the resistance of a conductor?

1. Explore the relationship between resistance and conductor materials

Connect copper wires and nickel-chromium alloy wires of the same length and thickness to the circuit respectively, close the switch, and observe the brightness of the small bulb in the circuit.

Experimental phenomena

By connecting different conductors, the brightness of the small bulb changes.

In the above experiment, connect the ammeter, observe the changes in the ammeter's indication, and continue to observe the brightness of the small bulb.

Experimental phenomena

When the copper wire is connected to the circuit, the ammeter will read larger and the small bulb will be brighter;

When the nickel-chromium alloy wire is connected to the circuit, the ammeter indicates a smaller value and the small bulb becomes darker.

2. Explore the relationship between resistance and conductor length

Conclusion of Experiment 1:

The resistance of a conductor is related to its length.

The same material and cross-sectional area, the longer the conductor, the greater the resistance.

3. Explore the relationship between resistance and conductor cross-sectional area

Conclusion of Experiment 2:

The resistance of a conductor is related to the cross-sectional area;

The same material and length, the larger the cross-sectional area of ​​the conductor, the smaller the resistance.

summary

1. Resistance - a physical quantity used to express the resistance of a conductor to electric current, represented by the letter R.

2. In the International System of Units, the unit of resistance is ohms, referred to as ohms, and the symbol is Ω.

3. If the voltage across the conductor is 1 volt and the current flowing through it is 1 amp, the resistance of this section of conductor is 1 ohm.

4. The resistance of a conductor is determined by its material, length, cross-sectional area and temperature, and has nothing to do with other factors.

practice

1. 0.2MΩ=______Ω=______KΩ

2. The length of two copper wires and nickel-chromium alloy wires with the same thickness and equal resistance is ( )

A. The copper wire is longer B. The nickel-chromium alloy is longer

C. Same length D. Unable to determine

3. Regarding the resistance of the conductor, which of the following statements is correct ( )

A. The greater the resistance of the conductor, the smaller the resistance of the conductor to the current.

B. The greater the resistance of the conductor, the greater the resistance of the conductor to the current.

C. Conductor resistance is related to current. The greater the current, the smaller the resistance of the conductor.

D. Conductor resistance is related to current. The smaller the current, the greater the resistance of the conductor.

4. Which of the following statements is correct ( )

A. The longer the conductor, the smaller its resistance.

B. The thicker the conductor, the greater its resistance.

C. The thinner the conductor, the greater its resistance.

D. When the material and thickness of the conductor are the same, the longer the conductor, the greater the resistance.

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For more information about the "Exploring Circuit Resistors and Rheostats" PPT courseware, please click the Explore Circuits ppt Resistors and Rheostats ppt tab.

"Resistors and Rheostats" Exploring Circuit PPT Courseware 4:

"Resistors and Rheostats" Exploration Circuit PPT Courseware 4 Demonstration Experiment 1. Observe the brightness changes of the dimmer light 2. Listen to the changes in the volume of the speaker. Think about it. If you move the wire clip along the pencil lead, how will the brightness of the small light bulb change? Why do you think the brightness of the light bulb changes like this?

"Resistors and Rheostats" Exploring Circuit PPT Courseware 2:

"Resistors and Rheostats" Exploring Circuit PPT Courseware 2 The teacher connects each component on the circuit board to the circuit. You carefully observe the changes in the brightness of the light bulb and think about the following questions: How does the change in the brightness of the light bulb indicate how the current passing through it changes? Changes in current in a circuit indicate...

"Resistors and Rheostats" exploring circuit PPT courseware:

"Resistors and Rheostats" Exploring Circuit PPT Courseware 1. Resistance 1. Concept: The _____ effect of a conductor on current is called resistance. Represented by the letters _____. 2. Unit: The international unit of resistance is _____, the abbreviation of _____ symbol is _____. Commonly used units include _____( ) and _..

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Update Time: 2024-09-08

This template belongs to Physics courseware Shanghai Science Edition Ninth Grade Physics industry PPT template

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