"Ohm's Law and Its Application" Ohm's Law PPT Courseware 2

Description

"Ohm's Law and Its Application" Ohm's Law PPT Courseware 2

Import new lesson

George Simon Ohm was born in Erlangen, Germany. He was a man of great genius and scientific ambition. He had been a middle school teacher for a long time. He always carried out scientific research unremittingly and made instruments by himself.

Ohm studied the current in a wire. He published his experimental results in 1826. In 1827, he summarized his experimental rules into the following formula in his book "Mathematical Research on Circuits": S = γE. In the formula, S represents the current; E represents the voltage, γ is the conductivity of the wire to current, and its reciprocal is the resistance.

In the early days of the discovery of Ohm's law, many physicists were unable to correctly understand and evaluate this discovery, and he was met with skepticism and sharp criticism. It was not until 1841 that the British Royal Society awarded him the highest honor, the Copley Gold Medal, that he attracted the attention of the German scientific community.

Ohm also proved in many of his works that: resistance is directly proportional to the length of the conductor and inversely proportional to the cross-sectional area and conductivity of the conductor; in the case of stable current, the charge is not only on the surface of the conductor, but also on the conductor's surface. movement across the entire section.

In memory of him, the physical unit for measuring resistance was named after ohm.

teaching objectives

1.Knowledge and skills

Understand Ohm's Law and be able to use Ohm's Law to perform simple calculations.

Ability to derive the relationship between resistances in series and parallel circuits based on Ohm's law and circuit characteristics.

2. Process and methods

Through calculations, students will learn the general methods for solving electrical calculation problems, develop logical thinking skills, and develop good habits for solving electrical problems.

Understand the meaning of equivalent resistance based on experimental phenomena and understand equivalent research methods.

3. Emotional attitudes and values

Through the introduction of Ohm's life, students can learn about the spirit of scientists who devote themselves to science and have the courage to explore the truth, and stimulate their enthusiasm for learning.

1. Ohm’s Law

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

(1) Ohm’s law expression:

I=U/R

I - represents the current in this section of conductor. Unit: Ampere (A)

U—represents the voltage across this section of conductor. Unit: Volt (V)

R - represents the resistance of this section of conductor. Unit: Ohm (Ω)

(2) Transformation formula:

U=IR

R=U/I

2. Series and parallel connection of resistors

Previously we have learned the laws of voltage and current in series circuits and parallel circuits.

In a series circuit, I = I1 = I2, U = U1 + U2

In a parallel circuit, I = I1 + I2, U = U1 = U2

If resistors are connected in series or parallel, is the total resistance greater or smaller than before?

(1) Resistors in series

Demo

1. Connect a fixed-value resistor R to the circuit as shown in the figure, close the switch, and observe the brightness of the bulb.

2. Then connect two resistors R with the same resistance in series and connect them in the circuit. Repeat the previous experiment.

formula derivation

In the series circuit, according to U=U1+U2 and U=IR

Get: U1=I1R1, U2=I2R2

Available: IR= I1R1+ I2R2

Because: I=I1=I2

So: R= R1+ R2

That is: the total resistance of the series circuit is equal to the sum of the series resistances

(2) Resistors connected in parallel

Demo

Connect two resistors of the same value in parallel, connect them in the circuit as shown in the figure, close the switch, observe the brightness of the bulb, and compare it with the brightness of the bulb when a resistor is connected.

in conclusion

The total resistance of the parallel resistors is smaller than the resistance of any of the individual resistors.

formula derivation

In a parallel circuit, according to I=I1+I2 and I=U/R

Obtain: I1＝U1/R1, I2＝U 2/R2

Available: U/R= U1/R1+ U 2/R2

Because: U=U1=U2

So: 1/R= 1/R1+ 1/R2,

That is: the reciprocal of the total resistance in a parallel circuit is equal to the sum of the reciprocals of the parallel resistances

Consolidation exercises

1. There are two resistors in a series circuit with resistance values ​​of 5Ω and 10Ω respectively. If they are connected to a 6V power supply, what will be the current flowing through them?

2. Two resistors are connected in series in a circuit. The voltage across the circuit is 27V. The resistance values ​​of the two resistors are 3Ω and 6Ω respectively. Please calculate the voltage across each resistor.

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"Ohm's Law and Its Application" Ohm's Law PPT courseware:

"Ohm's Law and Its Application" Ohm's Law PPT courseware teaching objectives 1. Understand the two proportional relationships 2. Understand the meaning of the two deformation formulas of Ohm's Law 3. Be able to use Ohm's Law to simply calculate the relationship between current, voltage and resistance: When When the resistance R is constant...

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Update Time: 2024-10-03

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

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