How to know how to use electricity safely?

Electricity is getting closer to people's production and life, and the problem of safe use of electricity is becoming increasingly prominent. Therefore, we must master the relevant knowledge of electricity use.

What will happen if we touch the metal wire with current? We know that the cause of our injury or death is current, but when current flows through our bodies, what effect will it have? Will you get burned? Will there be arrhythmia? We may not die immediately because of electric shock, but if we continue to hold live parts, it will eventually lead to death, that is, the longer the contact time, the smaller the resistance of our body, so the closer the current passes to the death toll.

Talk about the safe use of electricity, but why does the resistance of our body change with time? Of course, we are not stupid enough to cling to charged objects when we know that we have been electrocuted. In fact, we are "glued" to them. Why did you get an electric card?

When the current on the wire is large enough to cause hand muscles to contract, people who get an electric shock often hold on to the wire. At first, the current was not fatal, but the skin resistance decreased with time, and the current finally reached the lethal dose of 0. 1 amp. If someone is found "frozen" on a live wire, but he is still alive, he should be separated from the wire as soon as possible without endangering himself, otherwise he will die.

Speaking of why people get stuck on metal wires, let's look at an experiment first. This is a classic experiment dealing with nerve and muscle characteristics.

A frog's leg is hung on a brass crossbar embedded in an iron base. The frog's legs can also touch a part of the base, but each time they touch it, they will contract and immediately enter a state of spasm. When the spasm is released, the frog's legs will droop and touch the base again, so the spasm will happen again. What is the reason for this reaction?

Because of the different energy levels of conduction electrons in each metal, the potential difference will occur when the two metals contact. When the frog's leg touches the base, the transverse strut, the base and the frog's leg form a closed loop, and the current (those that conduct electrons) flows through this loop. The current stimulates the muscles of the frog's legs and makes them contract quickly.

Similarly, the metal wire does not hold our hands with electricity, but the muscles of our hands contract when the current flows, so that our hands hold the metal wire tightly. Therefore, electricians often use the back of their hands or fingers to move live wires or live wires when working. If this contact causes an electric current, muscle contraction will take their hands away from the wires. If you must touch the conductor with your palm, the result is likely to be "stuck" to the conductor.

Understand this truth, don't touch live wires in the future, remember to use the back of your hand. Of course, if you can't touch it, you'd better not touch it.

Generally speaking, the effects of currents with different voltages and resistances passing through the human body are as follows:

Less than 0.0 1 amp: tingling or no sensation;

0.02 Amp: Pain and being stuck by live parts;

0.03 Amp: respiratory disorder;

0.07 Amp: Breathing is extremely difficult;

0. 1 Amp: died of myocardial fibrillation;

Above 0.2 Ampere: No myocardial fibrillation, but severe burns and respiratory arrest.

Usually, the current intensity between 0. 1 ~ 0.2 amps is the most deadly, because this current amount causes myocardial fiber tremor, which is a kind of spastic convulsion in which the heart muscle is out of control. As a result, the blood flow stopped and people died soon.

But strangely enough, the current exceeding 0.2 ampere will only lead to cardiac arrest, and the heart can beat again after routine emergency measures. On the other hand, controlling electric shock is the only way to prevent myocardial fibrillation. Therefore, the current intensity in the range of 0. 1 to 0.2 ampere is more likely to cause death than the greater current intensity.

As mentioned earlier, the resistance of the epidermis is much greater than that of the body. Therefore, the amount of current passing through the human body generally depends on the resistance of the skin. 240 volts is enough to break the skin.

In addition, lightning strikes can also make us get an electric shock. We know that lightning contains huge electric energy, but there are many examples of people who are directly or indirectly hit by lightning surviving. Some people even stopped breathing for 20 minutes after being struck by lightning, but they recovered completely without obvious electric shock or brain damage caused by hypoxia. Some people think that this shock will temporarily change the brain's demand for oxygen.

Anyway, can't the victim have severe burns and cardiac arrest? How much energy (or electricity) has been absorbed by such victims?

If a large amount of current enters the victim's body, the person is likely to die of internal burns. However, if a person gets wet, lightning may not penetrate into the body, so most of the current flows down through the water layer outside the body. This is also the reason why soaked trees can be intact when they are struck by lightning.

In this case, the victim's breathing and heartbeat may be stopped by electric shock, but rapid artificial respiration can wake the victim up. In lightning, many victims are not directly hit by lightning, but by lateral blasting objects that directly hit objects, or knocked down by ground current generated by lightning.

It is mentioned in a document that many people who died because of lightning strike gave up rescue prematurely just because the rescuers thought they were dead. This is indeed a pity. Therefore, all people who are struck by lightning must be given routine first aid.

In addition, in the past, when there was no cable TV, when watching TV during thunder, the TV image would be very unstable, with great interference, and sometimes the TV would be destroyed.

In fact, as long as there is no outdoor antenna connected, there is generally no need to panic when using TV indoors. Because although lightning is fierce, it has already discharged the earth before entering the room. In the process of short-time discharge, most of its huge energy is converted into heat, light and other energy, so it will not cause harm.

Usually, when watching TV indoors during thunder, the interference on the screen and in the sound is mostly the radiation energy of lightning, not the energy of direct induction or discharge. This radiant energy generally won't damage the TV set. Now most families have installed cable TV, and even this problem is gone.

However, it must be emphasized that it is dangerous to use outdoor antennas or watch TV outdoors when it thunders. If you must see it, you must take lightning protection measures.

winding wire

Winding wire is a kind of conductive metal wire with insulating layer, which is used to wind the coil or winding of electrical products. Its function is to generate magnetic field through current, or to generate induced current by cutting magnetic lines, so as to realize the mutual conversion between electric energy and magnetic energy, so it is also called electromagnetic wire. Commonly used winding wires are enameled wire and winding wire, and conductive wire cores are round wire and flat wire. At present, copper wires are mostly used, while aluminum wires are rarely used. Because there is insulating material outside the conductor, the winding wires have different heat resistance grades.