"Ohm's Law" PPT courseware 5

Description

"Ohm's Law" PPT courseware 5

think about it

When the resistance is constant, the current in the conductor is equal to the voltage across the conductor.

When the voltage is constant, the current in the conductor is _____ with the conductor's resistance.

Self-study guidance

Please read carefully the content under "Ohm's Law" on page 78 of the textbook and answer the following questions after 2 minutes:

1. What is the content of Ohm’s law?

2. What is the formula of Ohm’s law?

3. What are the meanings and units of symbols?

Ohm's law

(1) Content: The current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.

(2) Formula: I=U/R

(3) The meaning and unit of the symbol

Use international units in formulas (units must be unified)

Unit of voltage U: V

Unit of resistance R: Ω

Unit of current I: A

For R = U / I it means that the resistance is numerically equal to the ratio of the voltage across the conductor to the current through the conductor.

So, for R = U / I, can it be said that the resistance of a conductor is directly proportional to the voltage across the conductor and inversely proportional to the current through the conductor?

Analysis: No, because the resistance of a conductor is an attribute of the conductor itself. Its size depends on the material, length, cross-sectional area of ​​the conductor, and some are also related to temperature. The size of the resistance will not change with changes in current and voltage, but is only related to its own factors.

Apply Ohm's Law

1. General steps for calculations using formulas:

(1) Read and review the questions (pay attention to the content of known quantities);

(2) Draw a circuit diagram based on the meaning of the question;

(3) Mark the symbols and numerical values ​​of known quantities and the symbols of unknown quantities on the diagram;

(4) Use physical formulas for calculation (the writing format must be complete and standardized).

1. Regarding the relationship between current, voltage and resistance, which of the following statements is correct ( )

A. The greater the resistance of a conductor, the smaller the current flowing through the conductor

B． The greater the resistance of a conductor, the greater the current through the conductor

C. The greater the voltage across a conductor, the greater the resistance of the conductor and the greater the current through the conductor

D. When the voltage across the conductor is constant, the smaller the resistance of the conductor, the greater the current flowing through the conductor.

2. When a voltage of 4 V is applied to both ends of a nichrome wire, the current flowing through it is 0.2A, then its resistance is ___Ω. If the voltage at both ends of the alloy wire increases to 16 V, its resistance is ___Ω. If you want to use an ammeter to measure its current, you should choose an ammeter with a range of ___A.

3. Regarding Ohm's law, which of the following statements is correct ( )

A. At the same voltage, the current and resistance of a conductor are inversely proportional

B． For the same conductor, the current and voltage in the conductor are proportional

C. Because resistance is a property of the conductor itself, the current is only proportional to the voltage across the conductor

D. The current in a conductor is related to the voltage across the conductor and also to the resistance of the conductor

Compliance test

1. In the experiment, the voltage across an unknown resistor was measured to be 5V, and the current flowing through it was 50mA. What is the resistance of this resistor?

2. The resistance of an iron is 0.1KΩ, and the current flowing through it during use is 2.1A. What is the voltage applied to the iron?

Entering the high school entrance examination

When the voltage across a resistor is 5V and the current through it is 0.5 A, what should be the resistance of the resistor? If the voltage across both ends increases to 20V, what is the resistance value of this resistor at this time? What is the current flowing through it?

1. When the voltage across a certain resistor is 6V and the current passing through it is 0.3A, then the resistance of the conductor is ____; when the voltage across the conductor is changed to 9V, the current passing through it is ____; when When no voltage is applied to both ends of the conductor, the current through the conductor is ____, and the resistance of the conductor is ____.

2. According to Ohm's law I=, the variant form R= can be derived. For this expression, the following statement is correct ()

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

B. The greater the current passing through a conductor, the smaller the resistance of the conductor

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

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

4. Connect a 5 Ω fixed value resistor and a sliding rheostat in series in a 3 V circuit. It is known that the voltage at both ends of the fixed value resistor is 1 V, then the current through the sliding rheostat is ____ A. At this time, the sliding rheostat The resistance of the varistor connected to the circuit is ____ Ω.

5. According to Ohm’s law, R=U/I can be obtained, then ( )

A. R is directly proportional to U and inversely proportional to I

B. R is proportional to U and has nothing to do with I

C. R is inversely proportional to I and has nothing to do with U

D. R is a property of the conductor itself and has nothing to do with U and I

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Update Time: 2024-11-19

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