To use the preview of presentations, create an account for yourself ( account) Google and sign in: https://accounts.google.com
Slides captions:
Hello!!! I hope you are in a great mood.
Lesson Objectives Educational: To help build students' knowledge of Ohm's law for the complete circuit. Introduce the concept of electromotive force, explain the content of Ohm's law for a complete closed circuit. To promote the development of logical thinking, independence, the ability to draw conclusions, analyze, generalize. 3. Ensure sanitary and hygienic standards during the lesson, the prevention of fatigue through a change in the activities of students. Educational: practicing the methods of educational and cognitive activity among students; the formation of skills to apply the acquired knowledge in mathematics and physics lessons in solving standard problems and explaining theoretical material; Developing: development of students' independence in the course of solving applied problems and in experimental search; development creativity students and cognitive interest;
Lesson objectives: Educational: the formation of key competencies of students by means of modern pedagogical technologies (learning-oriented learning technology, ICT, differentiated learning technology, problem-search technology, project method) and the introduction of a competent approach to the educational process Developing: the development of independent critical thinking and communication skills students when working in groups of shifts Educational: providing pedagogical assistance in choosing the direction of further education
Georg Ohm Yes, electricity is my soulmate, It will warm, entertain, add light. Ohm's experiments showed that current strength, voltage and resistance are quantities related to each other.
Repetition
Electric current is created Unit of current strength Unit of voltage Unit of resistance Ohm's Law Formula for a section of a circuit Current strength is measured by the formula A device for measuring current strength A device for measuring voltage A device whose resistance can be adjusted An ammeter is included in the circuit Formula for finding resistance The direction of movement is taken as the direction of current moving charged particles Amp Volt Ohm I=U/R I = q/ t Ammeter Voltmeter Rheostat in series R= ρ l/S of positively charged particles
When the conductors are connected in series, the total resistance of the circuit is equal to the Sum of all resistances When the conductors are connected in parallel, the current in the circuit ... Is equal to the sum of the currents When the conductors are connected in parallel, the voltage in the circuit ... Is the same on each conductor With a change in voltage or current in the circuit, the resistance ... Does not change
Calculate the current strength in the spiral of an electric stove connected to a network with a voltage of 220V if the resistance of the spiral is 100 ohms. 2. The current passing through the lamp filament is 0.3 A, the lamp voltage is 6 V. What is the electrical resistance of the lamp filament? 3. The current in the circuit is 2 A, the resistance of the resistor is 110 ohms. What is the voltage in the circuit? 2.2 A 20 ohm 220 V
Knowledge update. 1. Why did the extension cord work properly before, but then it suddenly caught fire? 2. What phenomenon happened? 3. What law should be investigated for a theoretical explanation of this phenomenon?
Conclusion 1: Ohm's Law for a circuit section: the current strength in a circuit section is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance.
Current-voltage characteristic of a conductor A graph that expresses the dependence of current on voltage is called the current-voltage characteristic of a conductor.
Conclusion 2: Ohm's Law for a complete circuit: Ohm's Law for a section of a circuit considers only that section of the circuit, while Ohm's Law for a complete circuit considers the impedance of the entire circuit. Both Ohm's laws show the dependence of current on resistance - the greater the resistance, the lower the current and vice versa.
I took pieces of cylindrical wire of arbitrary length from various materials and placed them one by one in a chain... Georg Ohm... Ohm's discovery was skeptically received in scientific circles. This was reflected in the development of science - say, the laws of distribution of currents in branched circuits were derived by G. Kirchhoff only twenty years later - and in Ohm's scientific career
Question Ohm's law for a section of a chain Ohm's law for a complete chain 1. What quantities does Ohm's law connect? 2. How is Ohm's law formulated? 3. Write the formula for Ohm's law 4. Write the units of measurement 5. Conclusion
Any non-electrostatic forces acting on charged particles are called external forces. That. on the charges inside the source, in addition to the Coulomb forces, external forces act and carry out the transfer of charged particles against the Coulomb ones.
E F to → F st → e F to → A B Forces of electrostatic origin cannot create and maintain a constant potential difference at the ends of the conductor (electrostatic forces are conservative forces) A current source is needed in which forces of non-electrostatic origin act, capable of maintaining a potential difference at the ends of the conductor
Ohm's law for a complete circuit The current in the circuit is directly proportional to the electromotive force of the current source and inversely proportional to the sum of the electrical resistances of the external and internal sections of the circuit. Current (A) EMF-electromotive force of the current source (V) Load resistance (Ω) Internal resistance of the current source (Ω)
If there is no EMF on the circuit section (there is no current source) U = φ 1 - φ 2 If the ends of the section containing the current source are connected, then their potential will become the same U = ε In a closed circuit, the voltage on its external and internal sections is equal to the EMF of the source current ε = U external + U internal
Short circuit In the event of a short circuit, R → 0, current
Calculate the short circuit currents Current source ε , V r , Ohm I short circuit, A Galvanic cell 1.5 1 Battery 6 0.01 Lighting networks 100 0.001 1.5 600 100 000
Types of fuses
Problem solving: No. 1 A galvanic cell with an EMF E = 5.0 V and an internal resistance r = 0.2 Ohm is closed to a conductor with a resistance R = 40.0 Ohm. What is the voltage U on this conductor? No. 2 To the battery with EMF and internal resistance r = 0.5 Ohm, connected a light bulb with resistance R = 100 Ohm. Determine the current strength in the circuit. № 3 Determine the EMF of the current source with internal resistance r \u003d 0.3 Ohm, if, when connected to the terminals of the current source, parallel-connected resistors R 1 \u003d 10 Ohm and R 2 \u003d 6 Ohm, the current in the circuit: I \u003d 3 A. IN
Problem solving: No. 1 A galvanic cell with an EMF E = 5.0 V and an internal resistance r = 0.2 Ohm is closed to a conductor with a resistance R = 40.0 Ohm. What is the voltage U on this conductor? Answer: U \u003d 4.97 V. No. 2 To a battery with an EMF and an internal resistance of r \u003d 0.5 Ohm, a light bulb with a resistance of R \u003d 100 Ohm was connected. Determine the current strength in the circuit. № 3 Determine the EMF of the current source with internal resistance r \u003d 0.3 Ohm, if, when connected to the terminals of the current source, parallel-connected resistors R 1 \u003d 10 Ohm and R 2 \u003d 6 Ohm, the current in the circuit: I \u003d 3 A. B Answer: 0.119 A Answer: 12.15V
draw an analogy
Test 1 The formula expressing Ohm's law for a closed circuit is written as: a) I = U / R b) c) d)
Test 2. Short circuit current can be calculated by the formula: a) b) c) d)
Test (getting ready for the exam) 3. The emf of a battery with an internal resistance of r = 0.2 ohms, when the resistance is connected to it R = 5 ohms is ... Current flows through the circuit I = 1.5 A. A) 3 V B) 12 V C) 7.8 V D) 12.2 V
Test (getting ready for the exam) 4. What is the internal resistance of a current source with EMF B, if, when it is closed by resistors Ohm and Ohm connected in parallel, a current flows in the circuit I \u003d 2 A. A) 26 ohm B) 1.45 ohm C) 12 ohm D) 2.45 ohm
Answers to the test: No. 1 No. 2 No. 3 No. 4 D C C B
Reflection A. I liked everything. I understood everything B. I liked it, but I didn’t understand everything C. Everything is the same as always, nothing unusual D. I didn’t like it
Read homework § 107-108, exercise 19 No. 5.6. Task (at home): When a light bulb was connected to a battery of cells with an EMF of 4.5 V, the voltmeter showed a voltage on the light bulb of 4 V, and an ammeter showed a current of 0.25 A. What is the internal resistance of the battery? Thank you for the lesson!
Current source specifications
The role of the current source In order for the electric current in the conductor not to stop, it is necessary to use a device that would transfer charges from one body to another in the opposite direction to that in which the charges are transferred. electric field. A power source is used as such a device.
A current source is a device in which some form of energy is converted into electrical energy. Exist different kinds power sources: Mechanical current source - mechanical energy converted into electrical energy. These include: an electrophorous machine (the machine's disks are rotated in opposite directions. As a result of the friction of the brushes on the disks, charges of the opposite sign accumulate on the conductors of the machine), a dynamo, generators. Thermal current source - internal energy is converted into electrical energy. For example, a thermoelement - two wires from different metals must be soldered from one edge, then the soldering point is heated, then voltage will appear between the other ends of these wires. They are used in thermal sensors and geothermal power plants.
Light current source - light energy is converted into electrical energy. For example, a photocell - when some semiconductors are illuminated, light energy is converted into electrical energy. Solar panels are made up of photovoltaic cells. They are used in solar batteries, light sensors, calculators, video cameras. Chemical current source - as a result of chemical reactions, internal energy is converted into electrical energy. For example, a galvanic cell - a carbon rod is inserted into a zinc vessel. The rod is placed in a linen bag filled with a mixture of manganese oxide and charcoal. The element uses a paste of flour on a solution of ammonia. When ammonia interacts with zinc, zinc acquires a negative charge, and the carbon rod acquires a positive charge. An electric field arises between the charged rod and the zinc vessel. In such a current source, coal is the positive electrode, and the zinc vessel is the negative electrode. A battery can be made up of several galvanic cells. Current sources based on galvanic cells are used in household autonomous electrical appliances, uninterruptible power supplies. Batteries - in cars, electric vehicles, cell phones.
- For the current to exist constantly, a device is needed that constantly moves charges from one ball to another (current source).
- In addition to the Coulomb forces, other forces act in it - third-party forces
- Nature is not electrical.
- Inside the source, they are directed against the Coulomb forces.
- The work of external forces along a closed trajectory is not equal to zero
- Third-party forces are non-potential forces; their work depends on the shape of the trajectory.
- Inside the current source, the charges move under the action of external forces against the Coulomb forces (electrons from a positively charged electrode to a negative one), and in the rest of the circuit they are set in motion by an electric field.
External forces set in motion charged particles inside all current sources: in generators at power plants,
in galvanic cells,
batteries, etc.
Alternator, Russia
Accumulator, Tyumen
Galvanic cells, USSR
The nature of outside forces
Current sources
third party force
power plant generator
Force exerted by a magnetic field on electrons in a moving conductor
Galvanic cell
(Volta element)
Chemical forces that dissolve zinc in sulfuric acid solution
The action of external forces is characterized by an important physical quantity called electromotive force (abbreviated as EMF).
The electromotive force in a closed loop is the ratio of the work of external forces when the charge moves along the loop to the magnitude of the charge:
EMF is expressed in volts: [Ɛ] = J/C = IN
- The inscription on the batteries 9 V - means that third-party forces do work of 9 J when moving a charge of 1 C. from one pole to another.
Description of the presentation on individual slides:
1 slide
Description of the slide:
2 slide
Description of the slide:
1. A voltage of 10V is applied to the ends of the circuit. Determine the current in each resistor if R1 \u003d R2 \u003d 2 Ohms, R3 \u003d 9 Ohms. 2. A 150W electric kettle is connected to a network with a voltage of 220V. Determine the current strength in its spiral, the resistance of the spiral. Option 2 A conductor with a length of 200m and a cross section of 2 mm 2 is included in a circuit with a voltage of 12 V. What is the current strength in the circuit? Two resistors of 10 and 50 ohms are connected in parallel in the circuit. In the unbranched part of the circuit, the current is 6 A. Determine the voltage across each resistor and the current flowing in each conductor.
3 slide
Description of the slide:
Current source. An electric current can occur if oppositely charged balls or plates of a capacitor are connected with a metal wire. However, such an electric current turns out to be short-lived: since the lack and excess of electrons on the plates is compensated by moving electrons, the electric field driving the charges weakens to zero.
4 slide
Description of the slide:
To further maintain the current in the conductors, a device called a current source is used. Inside the current source, a redistribution of positive and negative charges occurs, so that an excess of positive and negative charges appears on the two terminals of the current source (terminal "+" and terminal "-"). Forces of a non-electrostatic nature that carry out such a separation of charges are called external forces. When a metal conductor comes into contact with the terminals of a current source, such a distribution of charges is very quickly established on the surface of the wire that a constant electric field arises inside the conductor with a strength directed along its axis. In this case, the current strength in the entire conductor becomes constant, the charges move along a closed circuit.
5 slide
Description of the slide:
Any current source is usually characterized by the work of external forces Ast, which they perform with such a displacement of the charge q inside the source. The ratio is called the electromotive force (EMF) of the current source. The EMF is expressed in volts (1 V \u003d 1 J / 1 C), as is the potential difference.
6 slide
Description of the slide:
Table "Types of current sources and the principle of their operation" Electrophoretic machine Mechanical rotation of non-conductive disks with applied conductive areas, some of which on one of the disks is electrified by friction, leads to the accumulation of charges in a special device called a Leyden jar. Currently used mainly for demonstration experiments requiring controlled generation of large (up to tens of thousands of volts) voltages Galvanic cell Two different material immersed in a solution or other conductive medium. Due to irreversible chemical reactions taking place at the "solution - solid" boundary, electrons or charged ions are accumulated on the electrodes. In galvanic cells, the energy of chemical bonds accumulated during the synthesis of these substances is irreversibly converted into the energy of separated charges.
7 slide
Description of the slide:
Solar cell When some semiconductor materials are illuminated in contact with metals, there is a transfer of electrons from the metal to the semiconductor. Piezoelectric element During mechanical deformation of some crystals (for example, quartz), electrons move from one area of \u200b\u200bthe crystal to another
8 slide
"Georg Om" - He became, in particular, the best billiard player and speed skater at the university, he became interested in dancing. Georg Ohm was born on March 16, 1787 in Erlang in the family of a hereditary locksmith. Om enthusiastically plunged into sports. Since 1825, Om began to study galvanism. Lamp rheostat. Ohm's law for a circuit section.
"Current in the circuit" - From which pole of the current source and to which is the current direction considered? What are the parts of an electrical circuit? What experiment shows the dependence of current on voltage? How does the current in a conductor depend on the voltage at the ends of the conductor? What needs to be created in the conductor so that a current arises and exists in it?
"Kirchhoff's Law" - Idle mode of the energy source (XX). The balance of voltages in any circuit of the circuit. Kirchhoff's first law. Nominal operating mode of the energy source. Calculation of the power transferred to the load. Analytical expression of Kirchhoff's second law. Power source short circuit mode. Kirchhoff's laws and modes of operation of energy sources.
"Om Tok" - Worked as a teacher in Gotstadt (Switzerland). As the resistance of the conductor increases, the current decreases. German physicist. Current versus voltage I (U) Current versus resistance I(R). Abstracts of the lesson on the topic "Ohm's law for a section of the chain." Ohm devoted the last years of his life to research in the field of acoustics.
"Current characteristics" - Serial connection of conductors. Voltage measurement. Electromotive force. The dependence of the current strength on voltage and resistance. Conditions for the existence of a current. The resistance of metals. Current strength. Current work. Characteristics electric current. Current is a physical quantity. Parallel connection of conductors.
"Ohm's law for a circuit section" - The power dissipated is maximum. Ohm's law in differential form. Work and current power. Kirchhoff's rules for branched chains. Kirchhoff's second rule (a generalization of Ohm's law for a branched chain). Ohm's law. Ohm's law in differential form. The efficiency of the current source. By dividing work by time, we get an expression for power.
Loading...