"Relationship between Resistors in Series and Parallel Circuits" Ohm's Law PPT Courseware 5

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"Relationship between Resistors in Series and Parallel Circuits" Ohm's Law PPT Courseware 5

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. This law is called Ohm's law.

2. Formula: I＝U/R Unit: I (A) U (V) R (Ω)

3. Transformation formula: U=IR R=U/I

1. Series connection of resistors

The series connection of R1 and R2 in the circuit is equivalent to the effect of only R in the circuit.

2. Derive the total resistance of the series circuit

1. Circuit diagram:

Characteristics of series circuit current: I=I1=I2

Characteristics of voltage: U=U1+U2

3. Discussion: What are the characteristics of the total resistance of a series circuit?

The characteristic is: the total resistance of the series circuit is greater than the resistance of any one conductor.

This is equivalent to increasing the length of the conductor

Discussion 2: If there are n resistors R1, R2,..., Rn connected in series, what is their total resistance R equal to?

Total R＝R1＋R2+···＋Rn

n resistors of the same value are connected in series, the total resistance R = nR

[Example 1] Connect a 10Ω resistor and a 20Ω resistor in series to a power supply with a voltage of 6 volts. Find the current in this circuit.

Solution: R＝Ｒ1+Ｒ2

I =U/R=6V/30Ω= 0.2A

Example 2. It is known that R1=20 ohms and R2=60 ohms. What is the total resistance when R1 and R2 are connected in parallel?

Answer: The total resistance of R1 and R2 in parallel is 15 ohms.

summary:

1. The total resistance of the series circuit is equal to the sum of the resistances of each part R=R1+R2+R3+…+Rn

n resistors of the same value are connected in series, the total resistance R = nR

2. The reciprocal of the total resistance of a parallel circuit is equal to the sum of the reciprocals of the parallel resistances.

Class exercises:

1. In the circuit shown in the figure, the power supply voltage remains unchanged. If the varistor slider P slides to the left, then ( )

A. V1 indicates that the number is increasing, A indicates that the number is decreasing

B. V1 means the number is decreasing, A means the number is decreasing

C. V1 indicates that the number is increasing, A indicates that the number is increasing

D. V1 indicates that the number decreases, and A indicates that the number increases.

2. There are two resistors, R1=3Ω, R2=9Ω. Connect them in series and connect them to the circuit. Their total resistance is ______, the ratio of the current passing through them is I1:I2 =______, and the ratio of the voltages across them is U1:U2. =______.

3. In the circuit as shown in the figure, when the switch S is closed and the slider P moves to the right, the following is correct about the changes in the two numbers ( )

A. The indications of ammeter and voltmeter become larger.

B. The indications of ammeter and voltmeter become smaller.

C. The ammeter’s indication becomes smaller and the voltmeter’s indication becomes larger.

D. The ammeter’s indication becomes larger and the voltmeter’s indication becomes smaller.

Analysis of typical examples

[Example 1] In the circuit shown in Figure 8-2-3, the voltage between the two poles of the power supply remains unchanged. After the switch S is closed, while the slide P of the sliding varistor moves from b to a, the two tables Reading changes, which of the following is correct ( )

A. The readings of both meters become larger

B. The readings of both meters become smaller

C. The ammeter’s indication becomes smaller and the voltmeter’s indication becomes larger.

D. The ammeter’s indication becomes larger and the ammeter’s indication becomes smaller.

[Example 2] The resistance of an electrical appliance is 120 ohms. If the voltage across the electrical appliance is 1/4 of the total voltage of the circuit, a ____ ohm resistor should be connected to the electrical appliance. If you want to increase the total current in the circuit If the electrical appliance passes through it, a ____ ohm resistor should be connected to the electrical appliance ___.

[Example 3] In the circuit shown in Figure 8-2-5, the sliding rheostat is marked with "100Ω, 1A" and the power supply voltage is constant at 36V. When the switch S is closed, the current is 0.5A and the voltage is 0.5A. The number is 10V, find:

(1)The resistance of resistor R1;

(2) The resistance value of the sliding rheostat connected to the circuit at this time;

(3) If the ammeter range is 0~3A and the voltmeter range is 0~15V, find the resistance range of the sliding rheostat connected to the circuit.

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"Relationship between Resistors in Series and Parallel Circuits" Ohm's Law PPT Courseware 6:

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"Relationship between Resistors in Series and Parallel Circuits" Ohm's Law PPT Courseware 4:

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Update Time: 2024-07-30

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