"Resistance" Voltage and resistance PPT courseware

Description

"Resistance" Voltage and resistance PPT courseware

do you remember?

1. Current is formed by __________, and most of it is caused by the directional movement of _____. Generally, ______ does not move directionally.

2. Voltage is the reason why _____________ forms current

3. How many parts does the circuit consist of? What is the function of wire?

4. What materials are the conductor cores you have seen generally made of?

Connect copper wires and iron wires of the same length and thickness respectively. We observe the ammeter indication and the brightness of the light bulb respectively.

While wires carry current, they also hinder the directional movement of charges. In physics, this hindrance is called resistance.

1. Resistance of conductor

Resistance: represents the resistance of a conductor to the flow of electricity

The greater the resistance of a conductor, the greater its obstruction to current flow.

symbol for resistor in circuit diagram

Units of resistance: ohms, symbol

There are also kilohms and megaohms

1 megohm = 1000 kilohm 1 kiloohm = 1000 ohm

Common resistor values

Between human hands (dry) 1000—5000 Ω

Between human hands (moist) 200-800 Ω

Lighting bulb (when working) 100-2000 Ω

Small light bulb for experiment 5-50 Ω

Laboratory wires (each) 0.01—0.10 Ω

friendly reminder

1. The resistance of the wires we usually use is about one hundredth ohm. Because it is too small, we ignore it. In other words, we think that the wires have no resistance.

2. In physics, a component with a certain resistance value is often used, which is called a fixed value resistor.

3. The resistance of the ammeter is very small. We can ignore that the resistance of the voltmeter is very large, which is equivalent to an open circuit.

Now you know why the ammeter cannot be connected directly to the two poles of the power supply?

Now you know why the voltmeter can be connected directly to the two poles of the power supply?

Designing Experiments—Research Methods

It is conjectured that the size of the resistance may be related to three physical quantities. What kind of research method should be used to study whether the size of the resistance may be related to one of the physical quantities?

(1) Explore the relationship between the resistance of the conductor and the material

Variable: material

Quantitative: length, thickness,

Connect copper wires and iron wires of the same length and thickness respectively.

(2) Explore the relationship between the resistance and length of a conductor

Variable: length

Quantification: material, thickness,

(3) Explore the relationship between the resistance and cross-sectional area of ​​a conductor

Variable: cross-sectional area

Quantity: material, length

In conclusion

1. When the length and cross-sectional area are constant, the conductor resistance is related to the material.

2. When the material and cross-sectional area are constant, the resistance is related to the length. The longer the conductor, the greater the resistance.

3. When the material and length are constant, the resistance size is related to the cross-sectional area. The larger the cross-sectional area, the smaller the resistance.

4. When the temperature of most conductors increases, the resistance will increase.

Class summary

The resistance of a conductor is related to four factors: the material of the conductor, the length of the conductor, the cross-sectional area of ​​the conductor and the temperature of the conductor. Therefore, the resistance of a conductor is a property of the conductor itself and has nothing to do with other factors.

Classroom thinking questions:

1. Is resistance related to the voltage applied across the conductor and the current flowing through it?

irrelevant

2. Is resistance related to whether the conductor is connected to the circuit?

It doesn't matter, that is to say, the conductor has resistance whether it is connected to the circuit or not.

3. There are two wires of the same thickness and material. One is 20cm long and the other is 1.3 meters long. Which wire has greater resistance and why?

4. There are two wires of the same length and material, one with a cross-sectional area of ​​0.4cm2 and the other with a cross-sectional area of ​​2mm2. Which wire has a greater resistance and why?

5. For household electric lamps, the temperature when they are normally lighting is __________ higher than when they are not lighting. Therefore, the resistance at normal temperature is ____ than when it is lighting normally. Therefore, the current that can pass through the filament at the moment when the switch is closed is higher than the temperature when it is not lighting up. When _____, the filament tends to burn out the moment the switch is closed.

Class exercise: (Believe that you can do better)

1. There is a piece of thick copper wire. If it is stretched, its resistance will be _________; if it is folded into a wire and its resistance will be _________.

2. A conductor is connected to a circuit. When the voltage across it is 3V, the resistance of the conductor is 5Ω. If the voltage across it becomes 6V, the resistance of the conductor is ____Ω. If the voltage across it becomes 0V, the resistance of the conductor is ____Ω. The resistance of this conductor is___Ω

3. For copper wires A and B with the same thickness, the length of A is half of B, then the relationship between the resistances RA and RB of A and B is ( )

A. R A = 2R B B. 2R A = R B

C. R A = R B D. Can't compare

4. "The resistance of copper wires is smaller than that of iron wires." Is this statement correct? What should I say?

Keywords: Voltage and resistance teaching courseware, resistance teaching courseware, Lujiao version ninth grade physics PPT courseware download, ninth grade physics slide courseware download, voltage and resistance PPT courseware download, resistance PPT courseware download, .PPT format;

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

"The Relationship between Current, Voltage and Resistance" PPT courseware:

"The Relationship between Current, Voltage and Resistance" PPT courseware Part 1: Introduction of the topic Please look at the following experiment and think about the problem. Please think: What can be done to dim the light bulb? Method 1: Remove a battery Method 2: Add resistance to the circuit Question: Same...

"The Relationship between Current, Voltage and Resistance" PPT:

"The Relationship between Current, Voltage and Resistance" PPT Part One Content: Thinking: Which physical quantity is most susceptible to the magnitude of the current passing through a certain conductor in a certain circuit, the voltage at both ends of this conductor, and the resistance of this conductor, which physical quantity is most susceptible to the other two Due to changes in quantity...

"Conductivity and Resistance of Matter" PPT download:

"Conductivity and Resistance of Matter" PPT Download Part One: Life Examples Which objects in life easily conduct electricity? Which ones don’t conduct electricity easily? Coins, plastic rulers, glass pieces, pencil lead, salt water, chalk, purified water. How to design an experiment? 1. Judgment criteria..

File Info

Update Time: 2024-09-08

This template belongs to Physics courseware Lu Jiao Edition Ninth Grade Physics Volume 1 industry PPT template

Preview