Junior Circuit Analysis 20, Junior Circuit Analysis

First put in barium hydroxide and then neutralize the dilute sulfuric acid, so that the conductivity of the water is reduced, because the title says "barium hydroxide solution (sufficient)", so the alkalinity in the cup is enhanced, the conductivity increases, and the magnetism of the electromagnet becomes larger...

The solubility of barium hydroxide is very low and it starts to exist in the form of a precipitate and there is no chemical reaction so no electric current is generated, so the electromagnet is not magnetic at first. However, because the action of dilute sulfuric acid will gradually develop the BA ions on the surface of barium hydroxide towards a more stable barium sulfate precipitation, there is a reaction slowly, so an electric current is generated, so there is magnetism!

Dilute sulfuric acid will react with BaoH2 first, resulting in a decrease in ion concentration in the solution, a decrease in current flow, and a decrease in the magnetism of the electromagnet. After pH 7, if BaoH2 is added, the ion concentration will increase, and then the current will increase, and the magnetism of the electromagnet will increase.

Because when barium hydroxide is poured at the beginning, the sulfate ions and hydrogen ions in the dilute sulfuric acid are decreasing (the two react to generate non-conductive water and barium sulfate precipitate), so the magnetism of the electromagnet decreases, when the barium hydroxide consumes all the sulfate ions, the current basically becomes zero, and the magnetism of the electromagnet is zero, and then the hydroxide ions and barium ions in the excess barium hydroxide continue to participate in conduction, and there is a current in the circuit, so the electromagnet has magnetism again.

It looks quite complicated.,Physics and chemistry are used together.,There's a picture of the title, right? There should be something particular about the position of the magnet, right? Magnetism, it is estimated that it is affected by the current, and the addition of Ba(OH)2 should also be added slowly rather than poured in one breath, right?

H2SO4 is consumed first, the current decreases, and when it is consumed, Ba(OH)2 begins to be excessive, and it can conduct electricity again, and the current becomes larger again, and the magnet is magnetized again, right? It doesn't seem like the topic is very clear.

In addition, I wonder why the magnet doesn't react with H2SO4?

Add barium hydroxide to sulfuric acid, and the reaction equation is sulfuric acid + barium hydroxide = barium sulfate (precipitation) + water. When slowly added to Ri, hydrogen ions, sulfate ions, can be ionized; It is slowly reduced, and the water generated is very small in ionization, which can be ignored here and can be considered that water does not conduct electricity, and when hydrogen ions are added, sulfate ions are completely reacted. There is only water and barium sulfate left in the beaker, and when you add it, there will be a large number of barium ions and hydroxide ions in the beaker.

The reaction of dilute sulfuric acid and barium hydroxide will produce barium sulfate precipitation, the ions in the solution will gradually decrease, the conductivity will decrease, and when the sulfuric acid reaction is completed, it will not conduct electricity, and the concentration will gradually increase when the solution is added.

Magnetism is first reduced to 0 and then larger, when the power is just on, dilute sulfuric acid and barium hydroxide first react to cancel out the magnetism, after the reaction is completed, the magnetism will become stronger, because the compound produced by the reaction is a material with a magnet.

Junior high school physical circuit fault analysis method:

1. Circuit fault judgment method:

1. Judge short circuit or open circuit through the ammeter: if the ammeter has an indication, it will be short-circuited; If the ammeter does not indicate the number, the circuit will be opened.

2. Judge which electrical appliance is faulty through the voltmeter ammeter: when one of the voltmeter and the ammeter has an indication and the other has no indicator, the electrical appliance measured by the voltmeter is faulty; When both the voltmeter and the ammeter have no indication or both have an indicator, the other non-voltmeter is faulty.

2. Judgment method of open circuit and short circuit.

Judgment of the open circuit:

1. If the electrical appliances in the circuit do not work (often the light is not on), and there is no current in the circuit, the circuit is open.

2. There are two ways to judge the specific part of the open road:

If the voltmeter is connected in parallel with each place, there is an indication and it is relatively large (often expressed as equal to the power supply voltage); then the circuit between the two binding posts of the voltmeter is open (except for the power supply);

If the other parts can work normally and the ammeter has current, the part that is connected in parallel with the ammeter at that time is disconnected (applicable to the series circuit of multi-purpose electrical appliances).

Judgment of short circuit:

1. If some of the electrical appliances in the series circuit or series part cannot work normally, and the other parts of the electrical appliances can work normally, the part that cannot work normally will be short-circuited.

2. The voltmeter is connected in parallel with each part, and the voltage of the wire part is zero to indicate that the wire is normal, if the voltage at both ends of a certain electrical appliance is zero, the electrical appliance is short-circuited.

3. Use the ammeter to judge.

1. Analysis of the change of the original current representation in the circuit.

The indication increases. Description: Some consumers in the circuit (or branch) are short-circuited. (If all electrical appliances are short-circuited, the ammeter will be burned).

The indication decreases. Description: An open circuit has occurred in a circuit (or branch). The ammeter is broken.

The indication does not change. Note: An open circuit occurs on a branch other than the branch where the ammeter is located.

2. Analyze the ammeter and the circuit under test in parallel. (for series circuits).

There are indications. Description: An open circuit occurred on the circuit under test.

There is no indication. Description: An open circuit occurred on an untested circuit.

The circuit course in junior high school is very small, with only a little knowledge of electrical circuits, and there is no analysis and skills such as analysis.

The physics knowledge of junior high school is mainly to learn the circulation of circuits, and then explain the analysis methods of circuits to the students.

01 There are two basic methods of circuit connection: series and parallel.

02 Connection characteristics of series circuit: the whole circuit has only one current path, and each electrical appliance is connected in turn, without branch points.

03 Connection characteristics of parallel circuit: it is composed of trunk road and several branches, there are branch points, each branch road forms a loop with the trunk road, and there are several circuits on several branches.

04 The working characteristics of the series circuit: each electrical appliance affects each other, if one of the electrical appliances in the circuit does not operate, the rest of the electrical appliances will also fail to operate.

05 The working characteristics of the parallel circuit hail stove: each electrical appliance does not affect each other, even if the electrical appliances in a certain branch do not operate, the electrical appliances of other branches can still operate.

06 Switch control of series circuit: The control function of the switch has nothing to do with its position in the circuit, even if the switch position changes, it will not affect the change of the control source of the circuit.

07 Switch control of parallel circuit: the role of the trunk switch is not the same as that of the branch switch, the switch of the main circuit is the main switch, which controls the entire circuit, while the branch switch only controls the circuit where it is located.

Circuit faults are generally divided into two categories, short circuit and open circuit, but in the actual problem, we also need to analyze the specific fault phenomenon. Next, we will share the fault analysis method of physical circuit in junior high school for reference.

If the voltage representation number is zero, it means that there is a short circuit in the area. It should be noted here that the voltage between the wires is zero, indicating that the wires are normal.

Connect the small bulb in parallel in each part, if the small bulb does not emit light, it means that the electrical appliance is short-circuited. It should also be noted here that the small bulb that is connected to the wire part does not emit light, indicating that the wire is normal, because the small bulb is short-circuited at this time.

If the ammeter has a reading, the other parts can also work normally, indicating that the part connected in parallel with the ammeter has been disconnected.

If the voltmeter is equal to the power supply voltage, it means that the parallel part is disconnected. Because at this time, the voltmeter is equivalent to being connected in series in the circuit, and the number becomes larger.

A short circuit in the power supply means that in the circuit, the current does not flow through the electrical appliance, and is directly connected to the positive and negative poles of the power supply. According to Ohm's law i=u r, we know that since the resistance of the wire is small, the current on the circuit will be very large when the power supply is short-circuited. Such a large current, the battery or other power sources cannot withstand it, which will cause damage to the power supply; What's more, because the current is too high, the temperature of the wire will rise, and in severe cases, it may cause a fire.

Open circuit refers to the state that the circuit is not closed, or the wires are not connected properly, or the electrical appliances are burned out or not installed properly (such as connecting the voltmeter in series in the circuit), that is, the entire circuit is disconnected somewhere.

Circuit Failure Analysis Junior High School Physics has:

1. Resistance failure.

1. The voltage indication number is the power supply voltage, the ammeter has no indication (or the deflection is very small), move the slide, and the voltage indication number remains unchanged. (resistor r open).

2. There is no indication of the voltmeter, but there is an indication of the ammeter, and the current indication changes normally when the slide is moved. (Resistor r short circuit).

Second, the sliding rheostat is faulty.

1. The voltmeter and ammeter have an indication, the indication is small, and the moving slide blade changes the voltmeter and current indication number. (The sliding rheostat is connected to the bottom).

2. The voltmeter and ammeter have an indication, the indicator is larger, and the moving slide is moving, and the voltmeter and current indication remain unchanged. (The sliding rheostat is connected as above (or shorted)).

3. There is no indication of voltmeter and ammeter, and the fault is on the sliding rheostat. (Sliding rheostat open circuit).

3. Switch failure.

After connecting the last wire, the ammeter and voltmeter have an indication. (The switch is short-circuited, or the connection circuit switch is not disconnected).

Fourth, the fault is in the voltmeter and ammeter.

1. Close the switch, and the pointers of voltmeter and ammeter are reversed. (The positive and negative binding posts of the two tables are reversed).

2. Close the switch, the deflection amplitude of the voltmeter and ammeter pointer is too large. (The selected range for the two tables is too small).

3. Close the switch, and the deflection amplitude of the pointer of the voltmeter and ammeter is too small. (The selected range of the two tables is too large).

4. Close the switch, the voltmeter is the power supply voltage, the ammeter has no indication number, move the slider, and the voltage indication number remains unchanged. (The positions of the two tables are reversed).

5. Closing switch, voltmeter, ammeter, one of the indicators becomes larger, and the other indicates smaller. (The voltmeter is connected in parallel at both ends of the sliding rheostat).

6. Before closing the switch, the pointers of the voltmeter and ammeter are reversed. (not zeroed).

5. Miscellaneous. There is no indication of voltmeter and ammeter, and the fault is not on the sliding rheostat. (switch open circuit, ammeter open circuit).

Connected to a small range, moving the slide found that both representations were smaller. (The supply voltage is too low).

Basic Definition. 1. Look at the real thing to draw the circuit diagram, the key is to look at the diagram, the diagram can not be understood, you can not make a good diagram, there is an internal regulation in the high school entrance examination, mixed diagram is not required, then you should understand in your heart that the physical diagram actually has only two circuits, one in series, the other is in parallel, the series circuit is very easy to identify, first find the positive pole of the power supply, and use the tip of the pencil to advance the high order along the current side until the negative pole of the power supply. Clarify the position of each component and then draw it.

2. The order is: draw the battery pack first, make a standard drawing according to the order of the components, horizontal and vertical, there shall be no components at the turn, if there is a voltmeter, it should accurately judge which can measure the voltage of a circuit, and in the case of checking the circuit is correct, the voltmeter will be at both ends of the circuit under test.

3. For parallel circuits, the judgment method is as follows, starting from the positive pole of the power supply, find the bifurcation point along the current direction, and mark the Chinese "minute" character, use two pencils to start from the equinox point and advance along the current direction until the two nibs converge, this point is the confluence point. First of all, it is necessary to be clear how many branches there are, how many elements are in each branch, and what they are.

Specific steps: first draw the battery pack, draw two sections of trunk circuits respectively, draw branches between the equinox and the junction point, and accurately draw the components in each branch in order to draw the specification, the drawing requires horizontal and vertical, pencil drawing check is correct, draw the voltmeter to both ends of the circuit under test.

Identification errors: Circuits generally occur in the following situations.

1. Whether there is a short circuit in the power supply, that is, the current returns directly to the negative pole of the power supply without passing through the electrical appliance;

2. Whether there is a local short circuit, and the electrical appliances that are partially short-circuited cannot work;

3. Whether the voltmeter, ammeter and positive and negative binding posts are misconnected, or the range is not suitable;

4. The sliding balance pulse rheostat is misconnected (all up or all down).

The physical circuit diagram analysis skills for junior high school are as follows:

1. Several words and formulas involved in the circuit diagram.

1. "The voltmeter is connected to both ends of the xx", that is, the wires at both ends of the voltmeter can be connected to the two ends of the xx.

2. The principle of series voltage division and the principle of parallel shunt.

3. Open circuit: It is equivalent to the resistance of an electrical appliance suddenly becomes very, very large.

4. Short circuit: The resistance of an electrical appliance suddenly becomes very, very small.

2. Analyze the circuit diagram.

The connection method of the series circuit: The series circuit is very easy to identify, first find the positive pole of the power supply, and use the tip of a pencil to advance the current direction in order until the negative pole of the power supply.

The connection method of the parallel circuit: starting from the positive pole of the power supply, first complete the connection of a path, find the branch point, and then accurately connect the other branch.

If there are other electrical appliances on the wires connected to the power supply at both ends of the voltmeter, then we default to the voltage of the resistor remaining in the circuit.

3. The occurrence of general circuit errors occurs in the following situations.

1. Whether there is a short circuit in the power supply, that is, the current returns directly to the negative pole of the power supply without passing through the electrical appliance;

2. Whether there is a local short circuit, and the electrical appliances that are partially short-circuited cannot work;

3. Whether the voltmeter, ammeter and positive and negative binding posts are misconnected, or the range is not suitable (too large or too small);

4. The sliding rheostat is misconnected.