Junior high school physics What is a short circuit, junior high school physics judging short circuit

In physics, an electric current that is turned on directly without passing through an electrical appliance is called a short circuit. In the event of a short circuit, the machine is often damaged or caught fire due to excessive current.

In a series circuit, wires or switches are used to connect the two ends of the appliance directly. It is a local or partial short circuit.

If the two ends of the power supply are directly connected with wires, it is a short circuit of the entire circuit. It's easy to burn out the power supply.

Short circuits are divided into overall short circuits and local short circuits.

An integral short circuit means that the current flows directly from the positive pole of the power supply to the negative electrode without passing through the electrical appliance, which will burn out the power supply and wires.

A local short circuit is just that the electrical appliance does not work and will not burn out the power supply and wires.

That is, you use a wire to connect the positive and negative poles, and the electrical appliances in the middle are broken.

In physics, an electric current that is turned on directly without passing through an electrical appliance is called a short circuit. In the event of a short circuit, the machine is often damaged or caught fire due to excessive current.

In a series circuit, wires or switches are used to connect the two ends of a circuit component or load directly. (This is a local or partial short circuit that is required for a safety connection that does not cause burnout due to excessive current.) For example, in order to prolong its service life, when one of the filaments is broken and damaged, the special structure inside it will automatically connect the two ends of the small bulbs to make the other small bulbs work normally.

The wires are directly connected to both ends of the electrical appliances, so that the current is directly connected to the power supply through the wires through the electrical appliances, causing local overheating and causing fires, which will cause short circuits. There should be a detailed introduction in the textbook, and you can understand it by reading more books.

It is a direct connection between positive and negative There are no electrical components in the middle, the loop resistance is very small, and the current is very large!

A circuit that connects the two stages of the power supply directly with a wire without going through the electrical appliance is called a short circuit

Without passing through the electrical appliances, the two poles of the power supply are directly connected, which is called a short circuit. In general, high-voltage currents are generated and a large amount of heat is emitted.

In fact, it is not complicated at all, the neutral wire and the live wire are connected together and it is called a short circuit.

The wires are directly connected to the power supply stage.

The techniques for judging short circuits in junior high school physics are as follows:

1. According to Ohm's law i=u r, because the resistance of the wire is very small, the current on the circuit will be very large when the power supply is short-circuited. Therefore, if the current in the current is measured with an ammeter, if it is too large, it may be a short circuit.

2. In the circuit, if the current does not flow through the electrical appliances and is directly connected to the two poles of the power supply, the power supply will be short-circuited. Seeing this must be a short circuit.

A complete short circuit is a direct connection between the two poles of the power supply without passing through the electrical wires. When a complete short circuit occurs, the short-circuited appliances do not work, the voltage at both ends of the short-circuited appliances is 0 volts, and there is no current passing through the short-circuited appliances. At this time, the current in the connected line will be too large, and the power supply or ammeter may be burned.

A partial short circuit refers to the fact that an electrical appliance cannot work due to the presence of extra blank wires. When a partial short circuit occurs, the voltage at both ends of the short-circuited appliance is 0 volts, and the power supply voltage is used by another electr, and for the voltage, the electrical appliance with a larger voltage is the electrical appliance that occurs the short circuit. In the event of a partial short circuit, no current will pass through the short-circuited appliance.

Short circuit refers to the connection between phases or between phases (or neutral wires) outside the normal operation of the power system, and under normal circumstances, the phases are insulated or between phases and ground.

Middle School Physics. Summary of "short circuit" cases in electricity.

What are the common short-circuits caused by the phenomenon is a common fault in junior high school physics and electricity, and there are two types of common short-circuits from the structure of short-circuits: power short-circuits and local short-circuits. That is, in the circuit, the two ends of the electrical appliance are directly connected by wires, which is called local short circuit; In the other case, the power supply is directly connected with a wire without any electrical appliances, and the power supply is short-circuited.

In the two figures below, the power supply is short-circuited.

Common phenomenon:1Power Short Circuit:

The electrical appliances in the circuit do not work (e.g. small light bulbs do not emit light). There is a danger that the power supply and the entire circuit will burn out. 2.

Local short circuit: Local short circuit involves specific circuits, and the situation is varied. The following diagram is an example to illustrate a local short circuit, when the switch S is disconnected, two small bulbs are connected in series, and emit light.

When the switch S is closed, the bulb L1 is short-circuited, the bulb L1 does not emit light, while the bulb L2 still emits light (L2 brightness becomes larger, using Ohm's law.

and electrical power knowledge explained), ammeter.

The indication becomes larger. In the experimental problem of junior high school physics, a local short circuit only causes the electrical appliance to not work, but does not damage the electrical appliance, so it is allowed. Because it is variable, it is a difficult problem in electrical problems.

Other cases:1Excessive current in a circuit with an ammeter can damage the ammeter and form a short circuit. 2.From the components used to cause short circuits, common short circuits are: short circuit with wire, short circuit with switch, short circuit with ammeter, and sliding rheostat.

short circuit of the slide and so on.

Cause analysis: In the event of a short circuit, the current passes directly through the wire without passing through the electrical appliance. Qualitatively explained with the concept of resistance.

Resistance is the conductor's obstruction of the current, the electrical appliance always has a certain resistance, and the resistance of the connected wire can be regarded as zero, after the two ends of the electrical appliance are connected with the wire, the current will pass through the wire without resistance, and will not pass through the electrical appliance with resistance. A short circuit in the power supply is prone to fire. The current flows directly from the positive pole of the power supply to the negative pole of the power supply without passing through the electrical appliance, and the current in the circuit is extremely large.

Ohm's law: i=u r can be seen that when the power supply voltage u is certain and r is very small, the current in the circuit will increase instantaneously a lot, by Joule's law q=i2rt, the time t is certain, and the wire will heat up.

Heating up, and even fires.

The meaning is as follows:

A short circuit means that in a circuit, the current does not flow through the electrical appliance, but is directly connected to the two poles of the power supply, and the power supply is short-circuited. 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.

The difference between a short circuit and an open circuit.

A short circuit is when the positive and negative poles of a power supply are directly connected. There is voltage in the short circuit, and the power supply in the short circuit is extremely harmful. Because the resistance of the wire is very small according to i=u r, there is a large current in the circuit, which will burn out the electrical appliances.

An open circuit is when a normal circuit is broken somewhere. So there is no current, but the power supply is still there, so there is voltage.

The difference between a short circuit and an open circuit.

The so-called open circuit is a state in which a certain part of the closed circuit is disconnected and the current cannot be turned on, which is also called the open circuit state. When a circuit breaker occurs, the electrical equipment does not work, and the equipment in operation falls into a standstill or abnormal state.

A short circuit is a state in which the wires leading from a power source to an electrical device (also known as a load) are directly connected to each other without passing through the load (or the load is zero), also known as a short circuit state. That's the definition in the book. There is also a kind of short circuit that we often use, that is, there are more than two electrical appliances in series, and one is short-circuited with a wire (connected to both ends of the electrical appliance) to increase the current of the other.