2) Direction: Specify the direction of positive charge directional movement as the direction of current.
3) The charge passing through the conductor section within 1 sec is of the order of magnitude.
Series circuit parallel circuit
The current is equal everywhere.
I=I 1=I2
The total voltage across the series circuit is equal to the sum of the voltages of all parts of the circuit. Mathematical expression: U=U 1+U2 resistance relation: the total resistance of series circuit is equal to the sum of all series resistances.
R=R 1+R2+R3+…
Voltage-dividing function of series circuit: In series circuit, the voltage across the resistor is inversely proportional to the resistor.
The current in the trunk is equal to the sum of the currents in each branch.
I=I 1+I2
The voltage across each branch of the parallel circuit is equal to the power supply voltage, and the mathematical expression is: u = u 1 = u2.
Resistance relationship: the reciprocal of the total resistance of parallel circuit is equal to the sum of the reciprocal of each parallel resistance.
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When two resistors are connected in parallel. Total resistance R=
Shunt function of parallel circuit: the voltage at both ends of each branch of parallel circuit is equal.
I1r1= i2r2 = i3r3 = ir = u or
(1) Description: Resistance to parallel circuit.
(2) The total resistance is always less than the resistance of any road. (3)n The resistances of each resistance system are connected in parallel, and the total resistance is r/n..
(4) In parallel circuit, when one resistance decreases and the other resistance remains the same, the total resistance decreases, and vice versa.
(5) Current of parallel circuit: The greater the branch resistance, the smaller the current.
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.
(deformation formula: U=IR, that is, the principle of finding resistance by voltammetry)
(Only applicable to pure resistance circuits)
Four, use ammeter and voltmeter to measure resistance (voltammetry)
1, principle: the principle of measuring resistance by voltammetry is
2. Equipment: power supply, switch, lead, resistance to be measured, ammeter, voltmeter and sliding rheostat measure resistance by voltammetry;
3. Circuit diagram: When the circuit is connected, the switch is in the off state. Before the switch is closed, the sliding blade of the sliding rheostat should be at the maximum resistance.
I. Electric energy (electric work) w
1. In the process of current doing work, electric energy is converted into other forms of energy.
2. unit: the unit of electric work in the international system of units is J.
3. Measurement: Measure the work done by the current in the household circuit with an electric energy meter, (W=pt=UIt) 1 degree =1kwh = 3.6×106 J.
Electric power: W=UIt=Pt (applicable to all circuits) W= (generally applicable to pure resistance series circuits)
W= (generally applicable to pure resistance parallel circuits) W=UQ
Electric power (p)
1, which is a physical quantity indicating the working speed of current.
2. Formula: P=UI= (applicable to all circuits) P= (applicable to pure resistance series circuits)
P= (for pure resistance parallel circuit) Look at the nameplate to find the resistance:
The main unit of electric power is w, 1kw= 103w.
3. The brightness of the light bulb is determined by the actual power of the light bulb.
4. Measurement of electric power: When measuring the rated power of small bulbs, it is necessary to adjust the sliding rheostat to make the reading of the voltmeter equal to the rated voltage. At this time, the small light bulb emits light normally. Measure the ammeter and voltage indicator and calculate its rated power.
(Measuring electric power with electric energy meter)
In the series circuit of fixed value resistor and sliding rheostat, when the power supply voltage is constant and the resistance of sliding rheostat is equal to the fixed value resistor, the power of sliding rheostat is the maximum.
Two bulbs are connected in series, the bulb with large resistance is on (P=), the two bulbs are connected in parallel, and the bulb with small resistance is on (P=).
1) When two bulbs are connected in series, find the maximum voltage that can be applied across the circuit, and the circuit current should be the smaller rated current of the two bulbs (U=IR).
2) When two bulbs are connected in parallel, find the maximum main current, and the voltage at both ends of the circuit should be the smaller of the rated voltages of the two bulbs.
Look at the nameplate to find the current for the normal operation of the electrical appliance;
Using ammeter and voltmeter to measure the electric power of small bulb (voltammetry)
1, principle: the principle of measuring resistance by voltammetry is P=UI.
2. Equipment: power supply, switch, lead, small bulb to be tested, ammeter, voltmeter and sliding rheostat are used to measure resistance by voltammetry;
3. Circuit diagram: When the circuit is connected, the switch is in the off state. Before the switch is closed, the sliding blade of the sliding rheostat should be at the maximum resistance.
Joule's Law: It is a law that reflects blood rain when current passes through a conductor, and it is summarized from experiments. This law can be used to calculate the heat generated by current passing through a conductor.
2) When the electrical appliances in the circuit are all kinds of electric heaters, all the electric work is used for heating. At this time, when the electrical appliances in the circuit are not all electric heaters (such as motors and washing machines), W=UIt.
, W>q, and the formula is not available.
electromagnetism
1. Interaction between magnetic poles: magnetic poles with the same name repel and magnetic poles with different names attract.
2. There is a magnetic field around the current: Danish physicist Oster found that there is a magnetic field around the current.
3. Magnetic field of energized solenoid: There is a magnetic field around energized solenoid, and its magnetic induction line distribution is very similar to that of bar magnet. Its N-pole and S-pole and the direction of current can be determined by the right-hand screw rule (Ampere rule).
3. Principle of electromagnet: The energized solenoid is magnetic. The more turns of the energized solenoid, the greater the current and the stronger its magnetism. Inserting the iron core into the energized solenoid will greatly enhance its magnetism.
Advantages of electromagnet: the magnetism of electromagnet is controlled by the on-off of current; Its magnetic field strength is controlled by current; Its magnetic field direction is controlled by the current direction.
Second, the influence of magnetic field on current (motor)
1, Properties: A charged conductor will be subjected to a force in a magnetic field, and its direction is related to both the current direction and the magnetic field direction.
2. Application: motor (electric energy is converted into mechanical energy)
The motor is made by using the principle that the electrified wire is stressed in the magnetic field.
When the DC motor is working, the current direction needs to be changed automatically as soon as the coil turns to the balance position. The device that can accomplish this task is called commutator. Changing the direction of current or changing the direction of magnetic field can change the direction of motor rotation.
Third, electromagnetic induction (magnetoelectricity) (generator)
Electromagnetic induction was discovered by British physicist Faraday in 183 1 year.
2. Application: The generator uses the principle of electromagnetic induction to generate electricity. The generator converts mechanical energy into electrical energy.
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