Ice does not conduct electricity? Did you notice the physics knowledge in Nezha 2?

Review expert: Zhou Hongzhi, senior laboratory technician, master's supervisor, School of Physics and Optoelectronic Engineering, Beijing University of Technology

After watching the hit movie "Nezha: The Devil Boy Conquers the Dragon King", have you noticed a "physics law of cultivation"? When "Ao Bing as Nezha" and Shen Zhengdao were in a stalemate, physics knowledge came in handy - "Lightning conducts electricity in water! But Ao Bing's ice is an insulator!"

The structure of ice

Ice is a solid substance formed by water at low temperatures, and its molecular structure has certain special features. A water molecule (H2O) consists of one oxygen atom and two hydrogen atoms. The oxygen atom has a partial negative charge, and the hydrogen atom has a partial positive charge. They are bound together by covalent bonds, forming a high resistance substance due to the lack of free electrons.

Why doesn't ice conduct electricity?

Whether any material is conductive or not is reflected in its body resistance, that is, the number of free electrons or ions inside it. The more free electrons there are, the better the conductivity, and vice versa. This is what we usually say that the size of the conductive current depends on the size of the voltage and resistance.

In pure liquid water, there is a strong hydrogen bond between water molecules, and the number of free electrons that can be formed is extremely small. In solid ice, water molecules form a regular crystal structure through hydrogen bonds. There are fewer free electrons that can be used for conductivity, the body resistance is higher, and the natural conductivity is very poor.

Why does water conduct electricity?

The reason why water can conduct electricity in life is mainly because it can dissolve other substances, especially electrolytes.

When electrolytes dissolve in water, they break down into positive and negative ions. For example, when table salt (sodium chloride, NaCl) dissolves in water, it turns into sodium ions (Na⁺) and chloride ions (Cl⁻). These ions move freely in water, greatly reducing the body resistance of the water.

When voltage is applied to both ends of water, ions move to form an electric current. This is why water can conduct electricity. The quality of conductivity depends on the number of free ions contained in the electrolyte. The more free ions there are, the lower the bulk resistance and the better the conductivity.

Water in the natural environment usually contains various minerals and impurities, which can significantly increase the conductivity of water. Therefore, when we usually say "water can conduct electricity", we are actually referring to water containing impurities.

Note that the conductivity of ice changes depending on the following conditions:

0 1 Presence of impurities

If the ice contains dissolved salts (such as NaCl) or other electrolytes, these impurities will dissociate into free ions (such as Na⁺ and Cl⁻), which will make the ice have a certain conductivity. For example, when seawater freezes, the ice will show a certain conductivity due to the salt content.

0 2 Temperature change

When it is close to the freezing point (0°C), a very thin water film may form on the surface of ice. This water film contacts the air and dissolves into electrolytes, so that there are free-moving ions in the liquid water and it can conduct electricity. However, at extremely low temperatures (such as below -50°C), the electrolyte will be precipitated, which will further reduce the conductivity of ice.

0 3 High pressure environment

Under high pressure conditions, the crystal structure of ice may change, forming different forms of ice. The conductivity of these high-pressure ices may be different from that of ordinary ice, and related research is still ongoing.

After understanding the principle of water and ice conducting electricity, it is easier for us to understand how to ensure the safety of electricity use. The encounter between water and electricity is often accompanied by danger, so it is very important to master some basic knowledge of electricity safety.

When using electrical appliances, always make sure your hands and body are dry. Do not operate any electrical equipment when it is exposed to water, especially those that are not waterproof.

In a home environment, make sure all electrical cords and outlets are away from water and regularly check electrical cords for wear or damage. When using electrical appliances, follow the manufacturer's guidelines and do not overload appliances.

These fires must never be put out with water!

After a fire occurs, many people's first reaction is to put out the fire with water. In fact, this idea is wrong! When facing a sudden fire, you should calmly analyze the type of fire and put out the fire accordingly. The following fires must not be put out with water.

Electrical fire

If the power cannot be cut off, never use water or foam to put out an electrical fire because both water and foam can conduct electricity.

Carbon dioxide, dry powder fire extinguisher or dry sand should be used to put out the fire, and a distance of more than 2 meters should be kept from electrical equipment and wires.

Fire in high voltage electrical installations

Do not use water to put out a fire without a good grounding device or without cutting off the power supply. First, water is conductive and can easily cause equipment to short-circuit and burn; second, using water to put out a fire can easily cause high-voltage current to be transmitted along the water column to the fire-fighting equipment, causing electric shock and casualties.

This type of fire requires professional firefighters to put out the fire wearing relevant protective equipment after cutting off the power supply.