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Static electricity (description on high school level)

What comes to mind when you hear the term “electricity”? You can name stuffs like refrigerator, washing machine, television, light bulb, flash-light, computer, power plant and so on. When you are asked what electricity is, you can say it is behaviours of electrons.

Every matter is made of particles called atoms, in which there are nuclei and electrons move around the nuclei. A nucleus has positive charges and an electron has negative charges. There is usually a balance between positive charge of nuclei and negative charge of electrons in an atom. However, electrons go into or come out of a particle of atom. Then the balance will collapse and it will make a whole atom more negative or more positive. As a result of collection of such positively or negatively charged atoms, the whole stuff will have net charge.

But the question is: why does an electron have negative charge? I cannot explain this well because the negative charges of electron originate from elementary particles discussed in the field of nuclear physics. We will discuss, on senior-high-school-level, how matters with excessive charge behave and how electrons transfer between atoms – how electric current generate.

An atom that has lost electrons is positively charged and matters made of such atoms are, of course, positively charged. A charged matter is called a charged body. When you rub hair with a setting board (stationery), you can see the hair stand upwards. This is because hair tends to have positive charge and the setting board made of vinyl chloride is negatively charged easily. When both hair and vinyl chloride rub together, electrons inside the hair (strictly speaking, electrons in atoms making up hair) transfer into vinyl chloride so that hair has positive charge and vinyl chloride has negative charge. This is why, both positive and negative charges pull one another just like magnets.

Electricity held by matters like this is called static electricity. You might have ever felt a keen stimulus when touching a door knob made of iron in winter. That is because travelling of electrons between a positively-charged human hand and a negatively-charged door knob generate intense electricity with a few thousand volts instantly. There is a reason why such static electricity is not felt in summer. It is more humid in summer than in winter so that electricity travels via moisture in air.

The preference for a material to be positively or negatively charged depends on the constitution of electrons in the atoms. Atoms which are more likely to give off electrons tend to be positively charged. Ones which are more likely to accept electrons are negatively charged. What element has preference to more easily accept or give off electrons is described in the textbook for high-school-level chemistry (see constitutions of matters). Here is the tendency:

<< easily positively charged, ----------------------- easily negatively charged >>

human hands, hair, glass, cotton, paper, iron, gold, polyethylene, vinyl chloride


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