Knowledge points about two kinds of electric charges in physics

Charge, basic particles with positive and negative charges are called charges, positively charged particles are called positive charges, and negatively charged particles are called negative charges. Below are the knowledge points about the two types of charges in physics that I have compiled for you. Let’s take a look. Knowledge points about two kinds of electric charges in physics

Section 1 Two kinds of electric charges

1. The interaction between electric charges: like charges repel each other, and dissimilar charges attract each other.

There are only two kinds of charges in nature? The charge on the glass rod rubbed by silk is positive charge?+?; the charge on the rubber rod rubbed by fur is called negative charge?-?.

Charge: The amount of charge is called charge, or charge for short, and its symbol is Q. The unit of charge is Coulomb (C).

2. Methods to check whether an object is charged:

① Use an electroscope.

The structure of the electroscope: metal ball, metal rod, metal foil.

The principle of electroscope: Like charges repel each other.

From the size of the opening angle of the electroscope, the amount of charge can be judged. But an electroscope cannot detect whether a charged object carries a positive or negative charge.

②Use the interaction between charges.

③ Use the property of charged bodies to attract light and small objects.

3. Frictional electrification: Using friction to charge objects.

Under normal circumstances, the positive charge carried by the nucleus is equal in quantity to the total negative charge carried by all electrons outside the nucleus. The entire atom is neutral, that is, the atom is not electrically charged to the outside world. nature.

The reason for frictional electrification: due to the different abilities of the nuclei of different materials to bind electrons. When two objects rub against each other, the object whose atomic nucleus has a weak ability to bind electrons will lose electrons and become positively charged due to the lack of electrons. The object whose atomic nucleus has a strong ability to bind electrons will gain electrons and will be charged the same amount because of the excess electrons. of negative electricity.

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③ The friction between two objects composed of the same material will not generate electricity;

④ The friction to generate electricity does not create electric charge, but only transfers electric charge from one object to another, causing positive The negative charges are separated, but the total charge is conserved.

Energy conversion: mechanical energy - electrical energy

4. Conductors and insulators: Objects that easily conduct electricity are called conductors; objects that do not easily conduct electricity are called insulators.

Common conductors: metal, graphite, human body, earth, moist objects, water containing impurities, aqueous solutions of acid, alkali and salt, etc. Common insulators: rubber, glass, plastic, oil, ceramics, pure water, air, etc.

The reason why conductors conduct electricity easily: There are a large number of free charges in conductors (which may be positive or negative charges), and they can break away from the bonds of atomic nuclei and move freely inside the conductor.

The reason why insulators are not easy to conduct electricity: In insulators, almost all charges are bound within the atomic range and cannot move freely. (There is charge in an insulator, but the charge cannot move freely)

Metal conductors are easy to conduct electricity because of free electrons; aqueous solutions of acid, alkali and salt are easy to conduct electricity because of positive and negative ions

Conductors and insulators There is no absolute boundary between them, and they can transform into each other under certain conditions. Under certain conditions, insulators can also become conductors. Insulators cannot conduct electricity but can carry electricity. Physics Two Charge Exercises

1. Rubbing a glass rod with silk can make the glass rod charged; a rubber rod rubbed with fur will also be charged. How do you realize that the charges they carry are different?

2. A rubber rod rubbed against fur is charged ______. This is because the rubber rod ________ electrons (optional? gain? or? lose?) during friction.

3. The instrument commonly used in laboratories to test whether objects are charged is _______, which is made using the _______ principle.

4. The essence of frictional electrification is ( )

A. The nucleus is transferred from one object to another during friction

B. The nucleus is transferred during friction External electrons are transferred from one object to another

C. Atoms are transferred from one object to another during friction

D. Friction can create electric charge

< p> 5. As shown in the figure, two grass balls A and B are hung with silk threads. When ball B approaches ball A, the two balls repel each other. The following statement is correct ( )

A .Ball A is positively charged and ball B is uncharged

B. Ball A is uncharged and ball B is negatively charged

C. Ball A is positively charged and ball B is negatively charged

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D. Both balls A and B are negatively charged or both are positively charged

6. There are 4 light balls A, B, C, and D. It is known that C is positively charged , A and C attract each other, A and D repel each other, and B and D attract each other, then the following judgment is correct ( )

A. A is negatively charged, D is negatively charged, and B must be positively charged< /p>

B.A is negatively charged, D is positively charged, and B must be negatively charged

C.A is negatively charged, D is negatively charged, B may be positively charged, or it may not be charged

D.A is positively charged, D is positively charged, and B must be uncharged

7. Xiaohong saw an eye-catching slogan at the gas station: "Plastic barrels are strictly prohibited to transport gasoline." Why are plastic barrels not allowed to be used to transport gasoline, but metal barrels?

8. When Xiao Ming visited the Science and Technology Museum, a set of electrostatic experiments left a deep impression on him. After returning home, he drew a schematic diagram of the experimental situation. In the picture, A is a positively charged sphere placed on an insulating support, and B is a positively charged ball suspended by an insulating wire. Suspend ball B at P1, P2, and P3 at different distances from ball A (as shown in the figure).

(1) What is the reason why the ball deviates from the vertical direction?