The formula of actual power of electric power? Series parallel connection also has kilowatt hour conversion

The formula of actual power of electric power? Series parallel connection also has kilowatt hour conversion

The third part is circuit and current
[knowledge structure]
1、 Circuit composition:
1. Definition: the current path composed of power supply, electrical appliance, switch and wire
2. The function of each part of the components: (1) power supply: a device providing electric energy; (2) electrical appliances: working equipment; (3) switch: controlling electrical appliances or used to connect or disconnect the circuit; (4) wire: connecting to form a path for the charge to move
2、 Circuit status: path, open circuit, short circuit
1. Definition: (1) path: the circuit connected everywhere; (2) open circuit: the circuit disconnected; (3) short circuit: the circuit connecting the wire directly to the two ends of the consumer or power supply
2. Correctly understand the path, open circuit and short circuit
3、 The basic connection mode of circuit: series circuit, parallel circuit
4、 Circuit diagram (unified symbol, horizontal and vertical, simple and beautiful)
5、 Electrical materials: conductor and insulator
1. Conductor
(1) Definition: objects that conduct electricity easily; (2) reasons for conducting electricity: there are free moving charges in the conductor;
2. Insulator
(1) Definition: objects that are not easy to conduct electricity; (2) cause: lack of free moving charge
6、 The formation of electric current
1. The current is formed by the directional movement of charge;
2. There are positive and negative charges to form electric current. In the aqueous solution of acid and alkali salt, there are positive and negative ions, and in the metal conductor, there are free electrons
7、 Direction of current
1. Regulation: the direction of directional movement of positive charge is the direction of current;
2. The direction of current is opposite to that of negative charge;
3. Outside the power supply, the current flows from the positive side of the power supply to the negative side
8、 The effect of electric current: thermal effect, chemical effect and magnetic effect
9、 Current: I = q / T
10、 Measurement of electric current
1. Unit and its conversion: main unit a, common units Ma, μ a
2. Measuring tools and their usage: (1) ammeter; (2) measuring range; (3) reading method; (4) use of ammeter
Use the rules
11、 The law of current: (1) series circuit: I = I1 + I2; (2) parallel circuit: I = I1 + I2
[method tips]
1. The usage of ammeter can be summarized as (check two for confirmation, two for need and two for don't)
(1) First, check whether the pointer is on the zero scale line;
(2) Two confirmations: ① confirm the selected range; ② confirm the current value of each large grid and each small grid
The ammeter should be connected in series in the circuit to be tested; the current should flow in from the "+" terminal and flow out from the "-" terminal; the two don't: one is not to let the current exceed the selected range; the other is not to connect directly to the power supply without using electrical appliances
When the current is unknown in advance, the appropriate range can be selected by touch test
2. According to the characteristics of the series parallel circuit, solve the circuit of related problems
(1) The circuit structure is analyzed to identify the series or parallel connection among the circuit elements;
(2) Judge which section of the circuit the ammeter is measuring;
(3) According to the current characteristics of series parallel circuit, according to the given conditions, the current to be solved is obtained
The fourth part is Ohm's law
1、 Voltage
1. The function of the power supply is to provide voltage to both ends of the circuit; voltage is the cause of current in the circuit. If there is current in the circuit, there must be voltage; if there is voltage in the circuit, there may not be current, because it also depends on whether the circuit is a channel
2. The voltage is expressed by the letter U, the unit is volt, the abbreviation is volt, the symbol is v. the commonly used units are kilovolt (kV, 1kV = 103v) and millivolt (MV, 1mV = 10-3v). The voltage of home lighting circuit is 220V; the voltage of a dry cell is 1.5V; the voltage for human safety is not higher than 36V
3. Use of voltmeter: a. the voltmeter should be connected in parallel with the circuit under test; when the voltmeter is directly connected in parallel with the power supply, because the internal resistance of the voltmeter is infinite, the circuit will not be short circuited, and the measured voltage is the power supply voltage. B. the positive terminal of the voltmeter is connected to the positive terminal of the power supply, and the negative terminal is connected to the negative terminal of the power supply, Two ranges of "0 ~ 3V" and "0 ~ 15V" can be selected
4. Reading method of voltmeter: A. determine the range by looking at the terminal; B. look at the division value (how many volts each small grid represents); C. look at how many grids the pointer deflects, that is, how many volts there are
5. The batteries are connected in series, and the total voltage is the sum of the voltages of each battery
2、 Explore the law of voltage in series circuit
1. Experimental steps: A, ask questions; B, guess or hypothesis; C, design experiment; D, conduct experiment; D, analysis and demonstration, e, evaluation; F, communication (the general content is the same, some steps can be omitted)
2. In a series circuit, the total voltage is equal to the sum of the voltages of the consumers
3、 Resistance
1. Objects that are easy to conduct electricity are called conductors, such as pencil lead, metal, human body, earth, etc.; objects that are not easy to conduct electricity are called insulators, such as rubber, plastic, ceramics, etc.; objects that are between the two are called semiconductors, such as silicon metal, etc
2. The blocking effect of conductor on current is called resistance, which is expressed by R. the unit is Ohm, abbreviated as Ohm, and the symbol is Ω. The common units are kiloohm (K Ω, 1K Ω = 103 Ω) and megaohm (m Ω, 1m Ω = 106 Ω), and its symbol in the circuit diagram is
3. The factors that affect the size of resistance are: A, material; B, length; C, cross-sectional area; D, temperature. Generally speaking, after a conductor is manufactured, its resistance changes a little with the change of temperature, we approximately think that its resistance is unchanged, and it will not change with the change of voltage and current
4. When the temperature of some conductors drops to a certain temperature, their resistance will be zero, which is called superconductivity
5. The working principle of the sliding rheostat is: the resistance part is wound on the insulating tube by the resistance wire coated with insulating layer, and the resistance of the access circuit is changed by sliding on the slide. So the correct connection method of the sliding rheostat is: one up and one down. Its symbol in the circuit diagram is
It should be connected in series with the circuit under test
4、 Ohm's law
1. Ohm's law was induced by German physicist ohm in 1826
2. Ohm's Law: the current in a conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance at both ends of the conductor. The formula is: I = u / R, and the deformation formula is: u = IR, r = u / I
3. Note: A, unit must be unified, current a, voltage V, resistance Ω; B, this formula can not be understood as: resistance is proportional to voltage, and inversely proportional to current, because resistance is constant under normal circumstances
4. The voltage of electrical appliances in normal operation is called rated voltage; the current in normal operation is called rated current; but it often fails to reach this standard in life, so the voltage of electrical appliances in actual operation is called actual voltage, and the current in actual operation is called actual current
5. When there is a short circuit in the circuit (the power supply in the circuit is directly connected without using electrical appliances), according to I = u / R, because the resistance R is very small, the current will be very large, which will lead to fire
5、 Measure the resistance of the small bulb
1. According to Ohm's law formula I = u / R deformation r = u / I, we can calculate the resistance of the small bulb by calculating the voltage and current of the small bulb. This method is called voltammetry
2. Circuit diagram:
3. When measuring: A. before closing the switch, the sliding rheostat should slide to the maximum end of the resistance; B. when measuring the resistance, the rated voltage of the small bulb should be observed first, and then the voltage used in the measurement should be reduced from the rated voltage in turn. C. The average value of several measurement results can be obtained to reduce the error
4. During the measurement, the lower the voltage, the darker the small bulb and the lower the temperature, so the resistance will be slightly smaller
6、 Ohm's law and safe use of electricity
1. The voltage for human safety should not be higher than 36V, because according to Ohm's law I = u / R, under the condition of constant resistance, the higher the voltage, the greater the current through human body, so high voltage is very dangerous for human body
2. We can't touch electrical appliances with wet hands, because when people's skin is wet, the resistance will become smaller, which will increase the possibility of electric shock. Generally, don't get close to high and near charged body, don't touch low-voltage charged body
3. Lightning is a violent discharge phenomenon in nature, which is very dangerous for people, so when there is lightning phenomenon, don't stand under trees or other high conductive objects, or stand high
4. In order to prevent the harm of lightning to people, American physicist Franklin invented the lightning rod to let lightning enter the earth through metal conductor, so as to ensure the safety of people or buildings
Part V electric power
1、 Electric energy
1. Electric energy can be transformed into other forms of energy
2. Electric energy is expressed by W, the common unit is kilowatt hour (KWH). In physics, the common unit of energy is Joule (J), abbreviated as Joule. 1kwh = 3.6106j
3. Electric energy meter is an instrument to measure the amount of electric energy consumed in a period of time. A, "220 V" means that the electric energy meter should be used in 220 V circuit; B, "10 (20) a" means that the rated current of the electric energy meter is 10 A, In a short period of time, the maximum current does not exceed 20 A; C, "50 Hz" refers to the use of the meter in 50 Hz AC circuit; D, "600 revs / kWh" refers to each kilowatt hour of energy consumed by the meter, and the turntable turns 600 revolutions
4. The process of converting electric energy into other forms of energy is the process of doing work. The amount of electric energy converted is the amount of work done by the current. In essence, electric work is electric energy, also expressed in W. the common unit is Joule, and the common unit is kilowatt hour
2、 Electric power
1. Electric power is the physical quantity that indicates the speed of electric energy consumption, expressed by P, unit is Watt, abbreviation is Watt, symbol is w. commonly used unit is kilowatt (kw). 1kW = 103w, 1 horsepower = 735w. The definition of electric power can also be understood as: the electric energy consumed by electrical appliances in one second
2. The relationship between electric power and electric energy, time: P = w / T, in use, the unit should be unified, there are two kinds of units available: (1) watt for electric power (W), Joule for electric energy (J), second for time (s); (2) kilowatt for electric power (kw), kilowatt hour for electric energy (kWh, degree), hour for time (H)
3. 1kW hour is the electric energy consumed by 1kW electric appliances for one hour
4. The relation formula of electric power, voltage and current: P = I U unit: Watt (W) for electric power, ampere (a) for current and volt (V) for voltage
5. The electric power of electrical appliances working at rated voltage is called rated power
3、 Measuring the electric power of a small bulb
1. The circuit diagram for measuring the electric power of a small bulb is the same as that for measuring resistance
2. When measuring, it is necessary to measure the electric power of three times when the small bulb is too dark, normal light-emitting and too bright, but the electric power can not be calculated by the average value method, only the electric power when the small bulb is normal light-emitting
4、 Electricity and heat
1. When electric current passes through a conductor, electric energy is converted into heat. This phenomenon is called thermal effect of electric current
2. According to the electric power formula and Ohm's law, we can get: P = I2 R. this formula shows that under the same current condition, the power when electric energy is converted into heat is proportional to the resistance of the conductor
3. When the electric power of the power plant is fixed, the transmission voltage is inversely proportional to the transmission current, and the higher the voltage is, the smaller the current is. At this time, because there is resistance on the transmission line, according to P = I2R, it can be seen that the power supply voltage is lower than the current