Presentation on the topic "series and parallel connection of conductors." Serial and parallel connection of conductors. ammeter readings and total resistance

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Task 3.

Doctor Watson and Sherlock Holmes were invited to visit friends on New Year's Eve. And, suddenly, as one of Murphy’s laws says: “Everything that is supposed to break will definitely break, and at the most inopportune moment.” And what happened? When the owner of the house began to turn on the Christmas tree garland for the children, one of the light bulbs designed for a voltage of 3.5 V burned out. The children were upset, the owner was in a panic, because there was no spare light bulb at hand. We must save the holiday, Holmes decided. And, asking everyone to calm down, Holmes uttered the magic words and did one action. To the universal joy of the children, the garland caught fire. Later, Dr. Watson asked Holmes what he did? What did Holmes answer?

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Advantages and disadvantages of connections

Example of a serial connection: garland. Example of parallel connection: lamps in the office. Advantages and disadvantages of connections: Parallel - when one lamp burns out, the rest burn out. But when you turn on a lamp with a lower possible voltage, it will burn out. Series - lamps with a lower possible voltage are included in a circuit with a higher voltage, but if one lamp burns out, all of them will not light.

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Homework:

Give examples of series and parallel connections of conductors in your home. Rep. § 48, 49. Ex. 22 (2), exercise 23 (3,4).

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Repetition

Chizhova Vera Alexandrovna

Physics and computer science teacher

MBOU secondary school in Krasnoe village,

Nenets Autonomous Okrug.

• Speed ​​of charge movement along a conductor
• Charge passing through a conductor in 1s
• Denoted by ()
• Unit (A) ampere
• Measured by ammeter
• Depends on voltage and resistance (Ohm's Law)

• Voltage is the work done by an electric field to move a unit charge (1 C) along a conductor
• Identified by the letter (U)
• Measured with a voltmeter
• Unit of measurement (V) volt

• The property of a conductor to interfere with the movement of charged particles along the conductor under the influence of an electric field
• Denoted by R
• Unit of measurement (Ohm)
• Depends on the physical properties of the conductor

Laws of series connection of conductors

• The current strength is the same in all parts of the circuit
• The total resistance of the circuit is equal to the sum of the resistances of the individual sections of the circuit
• The total stress is equal to the sum of the stresses in individual sections

• 1) You need to make a Christmas tree garland from light bulbs. designed for a voltage of 6 V, so that it can be connected to a 120 V network. How many light bulbs do you need to take for this?

• A)4. B)8 C)16 D)20 E)30.

• 2) Determine the total resistance of the circuit, if the resistance of the supply wires is 2 Ohms, the included part of the rheostat
• 64 Ohm and 294 Ohm lamps (Fig. 159).

• 1. 240 Ohm; 2. 180 Ohm; 3. 100 Ohm; 4. 120 Ohm; 5. 360 Ohm.

• 3) When measuring the voltage on conductor R 1, it turned out to be equal to 12 V. When the voltmeter was connected to conductor R 2 , then it showed 45 V (Fig. 160). Calculate the resistance R 2 if R 1 = 40 Ohms.

• A)360 Ohm; B)135 Ohm; B)150 Ohm; D)4 Ohm; D)40 Ohm.

• 4) In each of the two heating elements of the boiler, the current strength is 5 A. Determine the current strength in the supply wires if the elements are connected in series.

• A)25 A; B)5 A; B)10 A; D) 2.5 A.

• 5) Conductors with a resistance of 2.4 and 6 Ohms are connected in series and connected to a network with a voltage of 36 V. Calculate the current strength in the conductors.

• A)3 A; B)0.33 A; B)432 A; D) 0.5 A; D) 0.3 A.

• 1) Current strength in the conductor R 1 is equal to 4 A. What is the current strength in the conductor R 2 (Fig. 161).

• A)4 A; B) 2 A; B) 8 A; D)16 A.

• 2) The resistance of the lamp is R 1 = 300 Ohms, and the voltage on it is 90 V. What will the voltmeter show if it is connected to a lamp with a resistance of R2 = 400 Ohms (Fig. 162)?

• A)240 V; B)180 V; B)100 V; D)120 V; D)360 V.

• 3) Three identical lamps are connected in series to a 120 V network (Fig. 163). What is the voltage on each of them?

• A)360 V; B)120 V; B)60 V; D)4 V; D)40 V.

• 4) Figure 164 shows a step rheostat in which resistance R 1= R 2= R 3=…= R 5=10 Ohm. Calculate the resistance at a given position of the moving contact K.

• A)20 Ohm; B)50 Ohm; B)40 Ohm; D)30 Ohm; D) 3.3 Ohm.

• 5) Electric lamp resistance R and the ammeter was connected to a 200 V network as shown in Figure 165. Calculate the resistance R , if the ammeter shows a current of 0.5 A. The lamp resistance is 240 Ohms.

• A)120 Ohm; B)160 Ohm; B)260 Ohm; D) 60 Ohm.

• A resistor with a resistance of 2 (Ohm) is connected to a circuit with a voltage of 12V. What resistance should another resistor be connected so that the current is 2A?

Repetition: series connection of conductors

• Two resistors and a light bulb are connected in a circuit with a source voltage of 12V. The voltage on the light bulb is 5V, on the first resistor 3V. The resistance of the second resistor is 6 (Ohm). Determine the resistance of the first resistor and the light bulb

• The current strength in the unbranched part of the circuit is equal to the sum of the currents in the branches
• The voltage on all parallel sections is the same
• The reciprocal value of the total resistance is equal to the sum of the reciprocal values ​​of the resistances of all parallel sections

Tasks for parallel connection of consumers

The resistor resistances are respectively 4,6,12(Ohm). Determine the current in each resistor if the voltage between points A and B is 24V. Determine the current strength in the unbranched part of the circuit

The current strengths in the resistors are respectively 2A, 1.5A, 3A. Determine the resistance of the resistors if the voltage between points A and B is 16V.

D/z § 48,49 exercise 22(1,2), exercise 23(3)

The experiment shows the relationship between current, voltage and resistance in a series connection. There are electrical circuits for serial connections and solutions to problems using these circuits.

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"Presentation for the lesson "Series connection of conductors."

Symbol

Name

Galvanic

Resistor

Ammeter

Voltmeter

Physical quantities and their letter designations.

Current strength

Voltage

Resistance

Ampere

Volt

Current strength

Voltage

Resistance

Physical quantities and instruments for their measurement.

Ammeter

Voltmeter

Current strength

Voltage

Georg Simon Ohm

Famous German physicist

Current (A)

I 1

I 2

Voltage (V)

U 1

U 2

Resistance (Ohm)

R 1

R 2

• With a series connection, the current strength in any part of the circuit is the same, i.e.

I = I 1 = I 2 .

The total voltage in the circuit in a series connection, or the voltage at the poles of the current source, is equal to the sum of the voltages in individual sections of the circuit:

U = U 1 +U 2

• The total resistance of the circuit when connected in series is equal to the sum of the resistances of the individual conductors:

R = R 1 + R 2 .

15 Ohm

20 Ohm

1. According to the diagram shown in Fig. 17, determine

ammeter readings and total resistance

in an electrical circuit, if R 1 = 5 Ohm, R 2 = 3 Ohm.

2. What are the ammeter readings and general

electrical circuit resistance,

shown in Fig. 18, If R 1 = 10 Ohm, R 2 = 2 Ohm?

3. According to the diagram shown in Fig. 21,

determine the ammeter readings and

resistance R2, if R1 = 4 Ohms.

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Using a series connection The main disadvantage of a series connection of conductors is that if one of the connection elements fails, the rest are switched off. So, for example, if one of the lamps of a Christmas tree garland burns out, then all the others will go out. This disadvantage can also turn into an advantage Imagine that some circuit needs to be protected from overload: when the current increases, the circuit should automatically turn off How to do this? (How to do this? (For example, use fuses) Give examples of the use of series connection of conductors

Application of parallel connection A variety of electrical energy consumers can be connected in parallel to the same electrical circuit. This scheme for connecting current consumers is used, for example, in residential premises. Question to students: How are electrical appliances connected to each other in your apartment?

Is it possible to use two identical lamps designed for 110 V in a 220 V network? How? How many identical resistors were connected in series if each of them has a resistance of 50 ohms and their total resistance is 600 ohms? Two resistors, the resistances of which are 5 Ohms and 10 Ohms, are connected in parallel to the battery. Which one has more current? How will the resistance of an electrical circuit change if you connect another resistor to any link in the circuit: a) in series b) in parallel? How should you connect four resistors whose resistances are 0.5 Ohm, 2 Ohm, 3.5 Ohm and 4 Ohm so that their total resistance is 1 Ohm? Check of knowledge