After view of the physical voltage in junior high school, physical voltage in junior high school

1. After all, voltage.

There is a current in the meter, and there is a sensitive galvanometer in the meter, although the resistance of the voltmeter is very large, it can measure a small current, even the current can be measured (1 microampere).

2. The open circuit can be regarded as no current in the wire, and the short circuit is a very large current, which can cause damage to the electrical appliances. (You can take the wire to connect the two poles of the battery directly, and then touch the wire and the battery with your hands, the wire is very hot, indicating that the current in the wire is very strong) 4. This is an example of an open circuit, the current flows directly from the positive electrode to the negative electrode, L1, L2 are not bright.

Explanation: It stands to reason that the current should be in every wire, but because the power supply also has a small resistance, when the current is very large, U=IR, the resistance in the power supply has a large voltage, and the wire and the bulb have a very small voltage, so the current in the bulb is very small, and the wire resistance is very small, and there is a current in the wire.

This is called a short circuit, which means that there is still very little current in the bulb and a lot of current in the wire.

A: 1When the current is turned on, a magnetic field is generated to rotate the pointer, and then calibrated according to the size, and the voltmeter actually has a weak current.

2.The two ends of the power supply are directly connected by wires without passing through any electrical equipment, which is called a short circuit. In the event of a short circuit, a very large current will occur in the circuit, which is called a short circuit current.

When the circuit is short-circuited, the short-circuit current may increase to far exceed the allowable current limit of the wire, causing the wire to heat up violently, and even burn the electrical equipment, leading to disasters. When the electrical equipment is working normally, the current in the circuit passes through the electrical equipment from one end of the power supply and returns to the other end of the power supply to form a loop. If the circuit of the Jiang circuit is cut or broken for some reason, the current in the circuit cannot flow, and the circuit cannot form a loop, which is called an open circuit.

3.In order to generate an electric current in a conductor, it is not enough to have only free electrons, but also to have certain external conditions. In order for a conductor to have a continuous flow of current, a certain potential difference must be maintained between the two ends of the conductor (usually guaranteed by the power supply), which is often referred to as voltage.

Just as water flows from a high water level to a low water level to form a water flow. The voltmeter and ammeter measure the voltage and current respectively in the circuit, the difference: the voltmeter is used in parallel in the circuit, and its compliance is v plus a circle; Ammeters are used in series in a circuit and their symbol is a plus a circle.

4.As shown in the figure given:

L1 and L2 are connected in parallel, when the three electric keys are closed, L2 is short-circuited by S3 and S2, and the current flows from S3 and S2 but not from L2, so L2 does not light up. (The current has a characteristic: when the current has different paths to flow through, it will choose the path with less resistance to flow through, and the resistance after the electric bond is closed is much smaller than the resistance of the bulb, so when there are two paths of the electric key and the bulb, it will pass through the electric key first).

And the current coming out of the positive electrode through S1 passes through L1, so L1 will light up.

1。Although the voltmeter is electric.

The resistance is very large, but it is also an electrical appliance, it can be regarded as an open circuit in the circuit, because its resistance value is relatively large compared to other electrical appliances, it is a electrical appliance that has almost no effect on the circuit, it is designed according to the relationship between voltage and current (U=IR), so it can indicate the voltage applied to it at both ends according to the tiny current flowing through it.

2。A short circuit is a connection in which the resistance is particularly small and the current is particularly large, which is likely to damage the circuit. Open circuit refers to a connection in which the resistance is particularly large, the current is particularly small, and the circuit is not working properly.

1. Current and circuit is the introduction to electricity, the concept of current is more abstract, and the current should be compared with the example of the image (such as: water flow) when explaining, so that students can understand the current and master the current.

Second, for simple circuit connections and circuit diagrams, the teaching method of teaching first and then letting students explore, and then the teacher correcting errors can play the following roles:

1.It can fully expose students' learning problems and make teaching more targeted;

2.It does not restrict students' thinking, and is suitable for the age characteristics of middle school students' good performance, which helps to stimulate students' curiosity and cultivate their interest in lifelong exploration;

3.Avoid students taking the students' content lightly as simple;

4.Let students experience the joy of success in the process of exploring and solving problems.

3. Let students find circuit components in life, so that students can fully embody that physics comes from life and is used in life.

Fourth, let students understand the simple circuits in life, help students understand the physics in life, help students to learn the knowledge they have learned in life, and are very helpful to cultivate students' interest and creative thinking.

The above is just for reference!

Ohm's law has its scope of application.

If this is not understood well, Ohm's law will not be used.

In a series circuit, there are two resistors, R1 and R2, and if the R1 resistance becomes smaller, then the total resistance becomes smaller. In the case of the power supply voltage (the total voltage does not change), the voltage is constant, and the current is inversely proportional to the resistance, so the current becomes larger.

The current is large, the voltage is large, and the scope of application of this law is "resistance does not change", that is, in this topic, R2 is constant, and the voltage of R2 does become larger.

At the same time, the voltage of R1 decreases because the sum of the voltages remains the same (equal to the supply voltage).

I don't know what to ask.

u1=r1*i r1 becomes smaller, current i becomes larger, how u1 changes, can not be discussed, only use u1 = u total -u2 to solve.

u2=r2*i, r2 does not change, i becomes larger, so u2 becomes larger so u1 becomes smaller.

Let's start with two phenomena.

We know that water flow is formed because the water is relatively high upstream and relatively low downstream. Because there is a height difference, the water forms a flow under the force of gravity.

Similarly, the flowing air forms the wind. So why does the air flow? This is due to the difference in air pressure between the two places. Because there is a difference in air pressure, wind is formed under the action of a horizontal air pressure gradient force.

The same goes for electric currents. In an external circuit, current can flow from the positive pole of the power supply to the negative pole of the power supply, which means that there is also a "pressure" between the positive and negative poles of the power supply. Under this "pressure" an electric current can be generated, and we call this "pressure" voltage.

In the first two phenomena, it is either the difference in height caused by the difference in the relative height of the water, or the difference in air pressure caused by the difference in air pressure. So what are the physical quantities that have a difference in electricity? This is called the potential difference.

Another name for voltage is called potential difference, which refers to the difference between two points due to the difference in electric potential. You don't care what the electric potential is now, you just need to know that since it is a difference, then it must involve two points, and one point does not matter whether it is a difference or not.

We can also analyze it in terms of work and energy. We know that when an electric current is passed through an electrical appliance, it converts electrical energy into other forms of energy. This process is the process of doing work with current, and the magnitude is calculated by w=uit.

The definition of current is the amount of charge flowing through a certain cross-sectional area of a conductor per unit time, that is, i = q t, and q is the amount of charge. So it in the formula can be written as q, and there is w=qu.

Let's analyze this equation. w is the work, and in mechanics we know that the work is the product of the force acting on the object and the displacement of the object in the direction of the force, w=fs. Applying this definition to electricity, that is, the electric charge moves a certain distance under the action of electricity.

So obviously, u in w=qu is a quantity related to distance, since there is a distance, can it still be a point?

First of all, the voltage is the difference between the electric potential: it is calculated as u=e*d (e is the strength of the electric field, d is the distance between two points), so theoretically a point has no voltage

That's because junior high school students have to establish a complete concept of electricity. The voltage is formed by two endpoints, i.e. there must be a reference point, which is the 0 point or public place. And one point cannot form a voltage.

A certain point cannot be said to be voltage, and voltage is the potential difference between two points. So, a certain point can only be said to be electric potential. The electric potential is not learned until high school physics, so junior high school cannot talk about the concept of electric potential, so you have to talk about the voltage at both ends.

Learning physics, from junior high school to high school, and to university, is a step-by-step study. What to learn and say at what stage cannot exceed the receptivity of each stage.

It's really good, the voltage should be.

The voltage at both ends, not at a certain point, there is no voltage at the point.

Take a good look at the textbook, there is a sentence in the first section of voltage: voltage is the cause of the directional movement of electric charges and the formation of electric current.

This will become clear when you get to high school to study physics. Now it's just a matter of knowing that the voltage refers to both ends of a certain circuit.

The full name of voltage should be called voltage difference, and the physics after high school is also called the potential difference, and the difference represents the difference, and the difference can only be made when two points are involved. When it comes to electric potential, it is easy to think of gravitational potential energy, the two are very similar, and I hope that when the questioner learns, he can compare and learn, and hope to adopt.

Voltage refers to the potential difference between two points. A point can only say what the potential is, not what the voltage is.

Electrons consume the potential energy they possess in the electric field after passing through the consumer, and the potential energy of a single current is extremely difficult to measure and calculate. And we can only control the electrical power of the electrical appliance, so we can use the difference between the left and right potential energies when the voltmeter is connected to the circuit in parallel to get an indication, and use the volts scalar. Therefore, there is a voltage only after the current passes through a certain distance and the potential energy is dissipated by the electrical appliance, and the potential energy of two points must be subtracted from the voltage to obtain the voltage.

There is no voltage at a certain point, i.e., the voltage is zero.

There is no concept of electric field in junior high school, so....

L1 and L2 are connected in parallel, so the overall resistance is 10*10 (10+10)du=5 in series with it, so the total resistance of the DAO line is 2+5=7

The total current of the line is the voltage divided by the resistance = 3 7 A, so the current of N1 = 3 7 A, the voltage = 3 7 * 2 = 6 7 V.

Then the current ratio of L1 to L2 is i1:i2=R2:R1, so the current of L1 is 3 14 A, the current of L2 is 3 14 A, the voltage of L1 is 15 7 V, and the voltage of L2 is 15 7 V.

If you add L5, then the overall resistance of the parallel connection is 10 3, and the rest of the algorithm is the same as above.

In the title, the fixed value resistor and the alcohol gas resistor are connected in series. When the concentration of alcohol gas increases, the resistance value of the gas resistor increases, and the resistance value of the fixed value resistance does not change, then the total resistance in the circuit becomes larger, the power supply voltage does not change, and according to Ohm's law i=u r, the total current in the circuit becomes smaller. The current in the series circuit is equal everywhere, so the current flowing through the fixed value resistance R also becomes smaller, but the resistance value of the fixed value resistance does not change, and according to U=IR, the voltage at both ends of the fixed value resistance becomes smaller.

The voltmeter measures the voltage across the R, so the voltage representation becomes smaller.

Another method is the voltage law in the series circuit, the voltage at both ends of each resistor (or component) in the series circuit is proportional to its resistance value, the larger the resistance value, the greater the voltage at both ends. In the question, the resistance value of the gas resistor becomes larger, so its voltage also becomes larger, because the total voltage, that is, the power supply voltage, does not change, so the voltage at both ends of the fixed value resistor becomes smaller, and the voltage representation number becomes smaller.

The voltage is based on the formula.

U=IR, because the gas resistor becomes smaller, the resistance of the whole circuit becomes smaller, so the current becomes larger.

U=IR, the resistance r does not change, the current becomes larger, so its voltage becomes larger.

You should know that the total power supply is fixed, so the total voltage does not change.

In fact, the problem is very simple, but the expression is too wordy, the process is like this, the alcohol concentration increases - resulting in an increase in the Q resistance value of the gas sensitive element, because the fixed resistance R does not change, the two resistors are connected in series, so the total resistance becomes larger.

The voltmeter is equivalent to an open circuit, so this circuit is a simple circuit in which the power supply, resistance, and ammeter are connected in series.

As the total resistance becomes larger and the size of the power supply remains the same, the number of current representations becomes smaller than the fixed resistance r measured by the voltmeter, and the number of current representations is the current of r, and the number of voltage representations decreases if r remains unchanged.

The circuit is connected to the power supply after the three lights are connected in series, according to the voltage distribution on the series circuit, because the three lights are the same, so the voltage at both ends of the three lamps is the same, V1 indicates the voltage after the two lights are connected in series, so the voltage at both ends of L1 and L2 is equal and equal to half of the value of V1, that is, 3V, and the voltage at both ends of the three lamps in series is equal to the sum of the voltages at both ends of V2 and L1, that is, the power supply voltage U, therefore.

u=3+6=9（v）。

The voltage is the magnitude of the voltage.