Repetition
Chizhova Vera Alexandrovna
Physics and computer science teacher
MBOU secondary school p. Red,
Nenets Autonomous Okrug.
- The speed of movement of charge along the conductor
- The charge passing through the conductor in 1 s
- Denoted by ()
- Unit (A) ampere
- Measured with an ammeter
- Varies with voltage and resistance (Ohm's Law)
- Voltage is the work of an electric field to move a unit charge (1C) along a conductor
- Indicated by the letter (U)
- Measured with a voltmeter
- Unit (V) volt
- The property of a conductor to interfere with the movement of charged particles along a conductor under the influence of an electric field
- Designated R
- Unit (Ohm)
- Depends on physical properties 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 the individual sections
- 1) It is required to make a Christmas tree garland of 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 the conductor R 1, it turned out to be 12 V. When the voltmeter was connected to the conductor R 2 , then he showed 45 V (Fig. 160). Calculate the resistance R 2 if R 1 \u003d 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 is 5 A. Determine the current 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; E) 0.3A.
- 1) The strength of the current in the conductor R 1 equal to 4 A. What is the current strength in the conductor R 2 (Fig. 161).
- A) 4 A; B) 2 A; C) 8 A; D)16 A.
- 2) The resistance of the lamp is R 1 = 300 ohms, and the voltage across 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 stepped rheostat, in which the resistances R 1 = R 2 = R 3 = ... = R 5 = 10 ohms. 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 strength of 0.5 A. The lamp resistance is 240 ohms.
- A) 120 ohm; B) 160 ohm; B) 260 ohm; D) 60 Ohm.
- In a circuit with a voltage of 12V, a resistor with a resistance of 2 (Ohm) is connected. What resistance must be connected another resistor so that the current strength is 2A
Repetition: serial connection of conductors
- In a circuit with a source voltage of 12V, two resistors and a light bulb are connected. 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 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 in all parallel sections is the same
- The reciprocal of the total resistance is equal to the sum reciprocals resistance of all parallel sections
Tasks for parallel connection of consumers
The resistances of the resistors are respectively equal to 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 equal to 2A, 1.5A, 3A. Determine the resistance of the resistors if the voltage between points A and B is 16V.
D / s § 48,49 exercise 22(1,2), exercise 23(3)
slide 2
Serial connection of conductors
With a series connection of conductors, the end of one conductor is connected to the beginning of another, and so on. The figures show a series connection circuit of two light bulbs and a diagram of such a connection. If one of the bulbs burns out, the circuit will open and the other bulb will go out.
slide 3
Serial Connection Laws
When the conductors are connected in series, the current strength in all sections of the circuit is the same: According to Ohm's law, the voltages U1 and U2 on the conductors are equal: The total voltage U on both conductors is equal to the sum of the voltages U1 and U2: where R is the electrical resistance of the entire circuit. It follows from this: When connected in series, the total resistance of the circuit is equal to the sum of the resistances of the individual conductors.
slide 4
Parallel connection of conductors
When the conductors are connected in parallel, their beginnings and ends have common points of connection to the current source.
slide 5
Laws of parallel connection of conductors
With a parallel connection, the voltages U1 and U2 are the same in all sections of the circuit: The sum of the currents I1 and I2 flowing through both conductors is equal to the current in an unbranched circuit: Writing on the basis of Ohm's law: where R is the electrical resistance of the entire circuit, we obtain When the conductors are connected in parallel, the value , the reciprocal of the total resistance of the circuit, is equal to the sum of the reciprocals of the resistances of parallel-connected conductors.
slide 6
Task 1 Two conductors are connected in series. The resistance of one conductor R \u003d 2 Ohm, the other R \u003d 3 Ohm. The reading of the ammeter connected to the first conductor is I = 0.5 Ohm. Determine the strength of the current flowing through the second conductor, the total current in the circuit, the total voltage of the circuit.
Slide 7
The solution of the problem
Given: R1= 2 ohms R2= 3 ohms I1= 0.5 A Solution: I1= I2= Iu; I2= Iu= 0.5 AU1= I1R1; U1= 0.5 x 2= 1 (V)U2= I2R2; U2= 0.5 x 3= 1.5 (V)Uu= U1+U2; Uu= 1+1, 5 = 2.5 (V) I2, Iu, Uu=? Answer: I2= Iu= 0.5 A, Uu= 2.5 V.
Slide 8
Task 2.
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Slide 14
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 should 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 children, one of the 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 thing. To the general joy of the children, the garland caught fire. Later, Dr. Watson asked Holmes what he had done? What did Holmes say?
slide 15
Advantages and disadvantages of connections
An example of a serial connection: a garland. Example of a parallel connection: lamps in an office. Advantages and disadvantages of connections: Parallel - when one lamp burns out, the rest burn. But when you turn on the lamp with a lower possible voltage, it will burn out. Serial - lamps with a lower possible voltage are connected to a circuit with a higher voltage, but if one lamp burns out, all will not burn.
slide 16
Homework:
Give examples of series and parallel connections of conductors in your home. Rep. § 48, 49. Ex. 22 (2), exercise 23 (3,4).
View all slides
The purpose of the lesson: 1. To introduce students to the series and parallel connection of conductors 2. The patterns that exist in a circuit with a series and parallel connection of conductors. Application 3. Teach how to solve problems on the topic: Series and parallel connection of conductors 4. Consolidate students' knowledge of various connections of conductors and form the ability to calculate the parameters of combined circuits
Advantages and disadvantages of serial connection Advantages: Having elements designed for low voltage (for example, light bulbs), you can connect them in series in the required quantity and connect to a source with high voltage (this is how Christmas tree garlands are arranged) Disadvantage: It is enough for one device (or element) to come out of building, as the circuit opens, and all other devices do not work
Advantages and disadvantages of parallel connection Advantages: If one of the branches fails, the rest continue to work. At the same time, each branch can be connected and disconnected separately Disadvantage: You can turn on devices designed only for this voltage
The use of a serial connection The main disadvantage of a serial connection of conductors is that if one of the connection elements fails, the rest are also disconnected. For example, if one of the Christmas tree garland lamps burns out, then all the others will go out. Mentioned drawback can turn into dignity Imagine that a certain 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 using a series connection of conductors
The use of parallel connection A wide variety of consumers can be connected in parallel in the same electrical circuit electrical energy Such a connection scheme for current consumers is used, for example, in residential premises. Question for students: How are electrical appliances connected to each other in your apartment?
Can two identical 110V lamps be used in a 220V 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, whose resistances are 5 ohms and 10 ohms, are connected in parallel to the battery. Which one has more current? How will the resistance of the electrical circuit change if one more resistor is connected to any link in the circuit: a) in series b) in parallel? How to 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
The experiment shows the relationship between current strength, voltage and resistance in series connection. There are electrical circuits for serial connection and problem solving according to these circuits.
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"Presentation for the lesson "Serial 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 devices 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 when connected in series, or the voltage at the poles of the current source, is equal to the sum of the voltages in the 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 scheme shown in fig. 17, define
ammeter reading and total resistance
in an electrical circuit if R 1 = 5 ohm, R 2 = 3 ohm.
2. What are the readings of the ammeter and the total
electrical circuit resistance,
shown in fig. eighteen, if R 1 = 10 ohm, R 2 = 2 ohm?
3. According to the scheme shown in fig. 21,
read the ammeter reading and
resistance R2 if R1 = 4 ohms.
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