"Exploring Ohm's Law" PPT courseware 2

Description

"Exploring Ohm's Law" PPT courseware 2

teaching objectives

1. Explore the relationship between current and voltage.

2. The relationship between current and resistance.

3. What is the use of sliding rheostat here.

4. Understand Ohm's law and use it to perform simple calculations.

Previously we learned:

1. Voltage is the cause of current. Will changing the voltage change the current? How will the current change?

2. Resistance is the resistance of a conductor to current. If the resistance of a conductor is changed, how will the current change?

Questions about the relationship between current, voltage, and resistance are what we will learn in this lesson.

How to study the changing relationship between the three physical quantities of current, voltage and resistance?

Control Variable

Control variable method, here are a few examples:

1. Study the factors affecting conductor resistance

2. Study the factors related to the effect of stress

3. What factors are related to the effect of research force?

4. What factors are related to the size of friction in sliding research?

5. Reasons that affect the speed of liquid evaporation

Detection Preview 1

Explore the relationship between current and voltage

What is the use of sliding rheostat here?

How to study the relationship between current I and voltage U?

R Same: Use the same conductor

U Different: Change the power supply, use one dry battery, two dry batteries, or three dry batteries

Conclusion one

The relationship between current I and voltage U:

When the conductor resistance is the same, the current through the conductor is proportional to the voltage across the conductor.

Detection Preview 2

Relationship between current and resistance.

What is the use of sliding rheostat here?

Use of Ohm's Law

How to study the change of current with resistance?

The experimental conclusion is: when the voltage is kept constant, the current is inversely proportional to the resistance.

The content of Ohm's law is:

The current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.

Ohm's law expression:

I=U/R

I - represents the current in this section of conductor.

U—represents the voltage across this conductor

R - represents the resistance of this section of conductor

think?

From the formula I=U/R, R=U/I is derived. The following statement is correct: [ ]

The greater the voltage A applied across the conductor, the greater the resistance of the conductor

BThe greater the current passing through a conductor, the smaller the resistance of the conductor

The resistance of C conductor is a property of the conductor itself and has nothing to do with voltage and current.

The resistance of conductor D is very large when the current is reduced to zero

(True or False)

1) The greater the voltage across the conductor, the greater the current passing through the conductor. ( )

2). The smaller the resistance of the conductor, the greater the current passing through the conductor. ( )

3) When the voltage at both ends of the conductor is the same, the greater the current passing through the conductor, the greater the resistance of the conductor. ( )

4). When the conductor resistance is the same, the greater the current passing through the conductor, the greater the voltage across the conductor. ( )

Application 1. Given voltage and resistance, find the current

The voltage of the lathe lighting is 36V, and the resistance of the filament is 32Ω when it works normally. Find the current through the filament.

Problem solving steps:

(1) Draw a circuit diagram

(2) List the known conditions and required quantities

(3) Solve I

Application 2: Given resistance and current, find voltage

In the circuit as shown in the figure, adjust the sliding rheostat R′ to make the bulb light normally. Use an ammeter to measure the current value passing through it to be 0.6A. It is known that the resistance of the bulb when it lights normally is 20Ω. Find the voltage across the bulb. .

Application 3: Given current and voltage, find resistance

A classmate used an ammeter in series with the light bulb and measured that the current when it glowed normally was 0.18A. Then he used a voltmeter to measure the voltage across the bulb which was 220V. Try to calculate the resistance value of the filament when it glows normally.

Class exercises

1. A conductor with a resistance of 4 ohms. After a voltage of 6V is applied to both ends of the conductor, the current flowing through it is ___A.

2. When a voltage of 4.5V is applied to both ends of a conductor, the current flowing through it is 0.3A. The resistance of this conductor is - ohms. If a voltage of 3V is applied to both ends of the conductor, the current passing through it is - A, and the resistance of the conductor is - ohms. If no voltage is applied to both ends of the conductor, the current flowing through it is - A, and the resistance of the conductor is - ohms.

summary

1. What is the content of Ohm’s law?

2. What is the expression of Ohm’s law? What are the transformation formulas?

3. What kind of research methods did we mainly use in this lesson?

Homework and preview

Homework: 2.3.4

Preview: application of Ohm's law, measurement of resistance by voltammetry.

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Update Time: 2024-11-23

This template belongs to Physics courseware Guangdong and Shanghai Edition Ninth Grade Physics Volume 1 industry PPT template

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