The problem of electricity in junior high school, a junior high school problem about electricity

Electric current, which refers to the directional movement of electric charges. Voltage is what causes the directional movement of charges in a circuit to form an electric current.

How voltage is formed has always been a question that physics today is trying to avoid. Because there is an irreconcilable contradiction between the theory of free electrons and the formation of voltage, the current theory cannot justify itself, so it is silent about the formation of voltage in matter, which is a disgraceful aspect of today's physics.

Voltage is an extremely important physical quantity in physics, and every student from middle school to university has done hundreds of exercises about voltage, how is voltage formed? There is no explanation in the textbook, and every student is at a loss.

How is voltage formed? Where does voltage come from and where does it come from? It is a question that many students have mentioned, and it has been a question that physics has tried to avoid for nearly a hundred years.

Why shy away? It is because the formation of voltage contradicts the current theory of electron cloud in which electrons outside the nuclear flow irregularly, and there is a deep contradiction between the formation of voltage and today's theory of free electrons in metals: if the electrons in the metal are sufficiently free, it cannot explain that the insulated metal conductor will form a very high voltage when some electrons are removed?

How can free electrons conduct electricity if they are not free in metals? Today's physics has chosen to avoid voltage in a dilemma.

What is Voltage? In university textbooks, it is said that "voltage is the difference between electromotive forces in an electrostatic field or between two points in a circuit" (in some books, the difference in electric potential).

There is a difference in electromotive force to form an electric current. It is mentioned in the book that the potential difference is provided by the power supply, and how the power supply forms the potential difference in the substance is mentioned in the word work. As for how to do the work, how to form a voltage in the substance, it has become an unspeakable secret, and I will not talk about it.

Generation of electric current: There are electrons bound around the proton, and the conductor is not charged without external force (such as magnetic field, voltage). When there is an external action (such as magnetic field, voltage), when the binding force of protons to electrons is less than that of external forces, the electrons move, thus forming a current ......

Current generation is not a conceptual ...... from a microscopic point of view

Voltage generation: The reason why water can flow in the pipe is because of the difference between high and low water levels, and the water can flow from high to low. The reason why the tap water used in the city can flow out of the pipe as soon as the water door is opened is because the tap water storage tower is higher than the ground, or because the pressure difference caused by the pump pushing the water.

The same is true for electricity, which is able to flow in a wire because of the difference between high and low potential energy in the current. This difference is called the potential difference, also known as the voltage.

The directional movement of the charge produces an electric current.

As we all know, the reason why water can flow in the pipe is because there is a pressure caused by the difference between the high and low water levels, so that the water can flow from high to low. The tap water used in the city can flow out of the pipe as soon as the water gate is opened, because the water storage tower is higher than the ground, or because the pressure difference caused by the water pump. The same is true of electricity, which is able to flow in a wire because of the difference between high and low potential energy in the current.

This difference is called the potential difference, also known as the voltage. In other words. In a circuit, the potential difference between any two points is called the voltage at those two points.

Voltage with a symbol"u"Denote. The level of voltage is generally expressed in unit volts, referred to as volts, and is symbolized"v"Denote. High voltages can be expressed in kilovolts (kv) and low voltages can be expressed in millivolts (mv).

Voltage is what produces electric current.

l is broken, both representations become 0, and a is excluded

R is broken, and the voltage of R is changed from the voltage measured by R in series to the voltage of the power supply, so the indication becomes larger, and the number of carrying current becomes 0

l short circuit, both indicate that the number becomes larger, exclude c

R short circuit, the number of Changbuvolt voltage is 0, the number of electric current is increased, correct, because D is correct, so B's must be absolute, and B is excluded from D

In the experiment shown in the figure, when the power is applied, we see the metal rod ab moving which shows that the energized conductor is subjected to a force in the magnetic fieldIf we want to make the metal rod ab move in the opposite direction, then we can change the direction of the pole while keeping the direction of the current constant; Or change the direction of the current while keeping the direction of the pole constant. If the direction of these two is changed at the same time, the direction of the metal rod AB motion is unchanged

From this experiment, we can conclude that the magnetic field energized conductor has the effect of ampere force, and the direction of its action is related to the direction of the current and the direction of the magnetic field.

w=u^2/rt

Parallel connection. The voltages of the two resistors are equal at both ends.

w is inversely proportional to r.

w1：w2=2：3

The node method is a method that simplifies the circuit diagram by drawing the method (you can use volts to determine whether the circuit is connected in parallel or in series) for easy judgment and calculation, and is specifically applied to draw an equivalent circuit diagram. Principle: The contact between the wire and the wire is a node, which does not move through the electrical appliance and does not change the circuit.

As shown in the figure on the left, at the junction of the wire and the wire, A, B, C, and D are marked respectively, and these four points are the nodes of the circuit. Move these nodes to get the right defective lap diagram circuit, make the circuit more intuitive, and facilitate our judgment, which is the equivalent circuit diagram drawn by the node method.

I advise you to take a look at the basics. Above.

In fact, the node method is not simple and straightforward. There is a concise approach to the identification of physical circuits in junior high school.

Give it a name, let's call it the "removal method" (based on the fact that the parallel circuit does not affect each other, that is, the on/off of any electrical appliance does not affect the rest of the electrical appliances. [Except for short circuits].

Borrowing the circuit diagram of "347095545" netizens to illustrate:

1. Arbitrarily remove two components (electrical appliances), such as L1 and L2, and observe whether L3 can work. (Whether the current can flow from the positive electrode to the negative electrode through L3).

2. Remove the remaining two components in turn, and observe and analyze whether the remaining electrical appliances can work. (Pay attention to the direction of the current path).

3. After completing the above wax loss analysis, the circuit can be sorted out (according to the direction of the current).

Note: The series circuit does not need to be analyzed, no matter how it is bent, there is always only one current path to open the wheel. Sikong letter.

w=u 2 r, w becomes 4 times, r does not change, it means u becomes 2 times.

According to the proportionality of the voltage of the series circuit and the block, r1=r is obtained

A1: If the total resistance is also constant, the current and voltage are constant.

A2: The total resistance of the circuit increases, so the trunk current (total current) decreases; Whereas, for parallel circuits, the voltage division becomes larger as the resistance increases. Therefore, the current indicates that the number becomes smaller, and the voltage indicates that the number becomes larger.

A3: The voltmeter measures the voltage of the resistor connected in parallel with it, and the ammeter measures the current of the resistor connected in series with it.

A4: Yes, but it must be the voltage on the same section of resistance, if the current Q2 is changed to series, the current representation number is still smaller, and the voltmeter depends on how to connect it with QQ to chat more conveniently, you hi I put.

(1) The junior high school is an ideal power supply, the voltage does not change with the change of external current, in fact, there is an internal resistance inside the power supply, so that the output voltage decreases with the increase of external current. Don't think about that. It can be considered that the voltage is constant, but the current changes with the change in the resistance value.

2) The parallel connection of a resistor in the circuit will inevitably reduce the total resistance, i=u r can be seen, and the voltage will not change, and the current will increase. Remember this sentence, shunt in parallel, divide pressure in series.

3) The ammeter is connected to the measured circuit, and the voltmeter is not as measured in the circuit (4) U=RI current and resistance are inversely proportional, and have nothing to do with what circuit it is in.

Q1: Whether the total current changes or not depends on whether the resistance in the circuit changes, if the resistance becomes larger, the current becomes smaller, and the resistance becomes smaller, the current becomes larger; The total voltage is constant;

Q2: When a resistor is connected in a parallel circuit, if a new resistor is added on the basis of the original resistance of a branch, the current representation number on the trunk circuit becomes smaller, and the voltage representation number remains unchanged; If a new branch is added, the total current will increase and the voltage indication will remain the same.

q3；According to the figure, it is necessary to see who the voltmeter is connected in parallel with is to measure the voltage at both ends, and who the ammeter is connected in series with is to measure the current through whom;

Q4: When the voltage is constant, the current is inversely proportional to the resistance, which is suitable for parallel circuits and when the two ends of the power supply are connected with different resistors, it is not very practical to connect the current of the series circuit in series

1.The total voltage is constant, and the total current depends on the total resistance.

2.The number of current representations becomes larger, and the number of voltage representations does not change.

3.Take the circuit, let's look at it specifically.

4.In a series circuit, the currents are equal everywhere and the voltage division is proportional to the resistance. In a parallel circuit, the voltage of each branch is equal to the total voltage, and the current is inversely proportional to the resistance.

Q1: No change.

Q2 It depends on how big the resistance is.

Q3: Draw a circuit diagram (don't tell me you can't draw it).

Q4: It can be used so to speak.

Q2 adds: In the series circuit, it is connected to another resistor, and the current and voltage will be reduced. A resistor of 0 (a smaller resistor can also be added) and a large supply voltage can be damaged. In general, they are all out of the range of the voltmeter and ammeter.

You can refer to o( o thank you.

I need to explain it in detail...How specific is this, let's do more questions...If you have these, you won't have time to help you, q573367264