Junior high school physics and electricity part of the knowledge of the sparse understanding

Electricity: parallel u1 = u2 = u i1 + i2 = i 1 r1 + 1 r2 = 1 r in series u1 + u2 = u i1 = i2 = i r1 + r2 = ri=u r u=ir r=u i

p=w/t w=pt t=w/p

w=uit w=i squared rt w=u squared t rp=ui p=i squared r p=u squared rq=

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Trouble, give you a lecture I don't know if it's enough for an afternoon!

Electrical knowledge points Charge: An object has the property of attracting small and light objects, and we say that the object is charged, or charged.

Triboelectric Activation: Frictional objects have the phenomenon of attracting small and light objects. Causes of triboelectric activation:

During friction, electrons are transferred from one object to another, and the object that gets the electron is negatively charged because it has excess electrons, and the object that loses electrons is positively charged by the same amount due to the lack of electrons.

Two charges:

1. Positive charge: The charge carried by the glass rod rubbed by silk is called positive charge.

2. Negative charge: The charge on the rubber rod that has been rubbed by the fur is called negative and positive charge.

The law of charge action: the same charge repells each other, and the different charge attracts each other.

Electroscope: Structure: metal balls, metal rods, metal foils. Purpose: To check whether the object is charged or not.

Principle: The same kind of charge repels each other.

The method of testing whether the object is charged 1 is to see if it can attract light and small objects, and if so, it will be charged;

2. It is the use of the electroscope, the object touches the metal ball of the electroscope, and if the metal foil is opened, it will be electrified.

Amount of charge: The amount of charge is called the amount of charge; Unit: Coulomb, Symbol: C.

Elemental charge: Electrons (discovered by Thomson) are particles with a negative minimum charge, and people call the minimum charge a elemental charge. e=。

Conductor; Objects that are good at conducting electricity. Such as: metal, human body, earth, aqueous solution of acid and alkali salt, graphite, etc.

Conductors conduct electricity for reasons: There are charges in conductors that are able to move freely. (In metals, it is free electrons that conduct electricity).

Insulators: objects that are not good at conducting electricity, such as: rubber, ceramics, plastics, dry air, oil, etc.

Causes of insulator insulation: Charges are almost all bound within the atomic range and cannot move freely.

Circuit composition 1. Power supply: a device that provides electrical energy and converts other forms of energy into electrical energy. Such as: generators, batteries.

2. Electrical appliances: devices that consume electric energy and convert electrical energy into other forms of energy.

3. Switch: control the on/off of the circuit.

4. Wire: connect the circuit to transmit electric energy.

Circuit Diagram: A diagram that symbolizes the connection of a circuit.

Diodes are unidirectionally conductive (light-emitting diodes also emit light).

Series and parallel series 1, connection characteristics: one by one, end to end.

2. Current path: only one.

3. Switch function: It can control all electrical appliances at the same time, and the control function remains unchanged when the switch position changes.

4. Work with electrical appliances: influence each other.

Parallel:

1. Connection features: parallel connection, head to tail.

2. Current path: at least 2.

3. Switch function: trunk circuit: main switch, control the whole circuit. Branch: Only control this branch.

4. Work with electrical appliances: do not affect each other.

Junior high school electromagnetic knowledge, mainly learn three laws and their applications:

1.The magnetic field generated around an energized conductor (electromagnetism), the Oersted experiment, and the magnetic field distribution of the energized spiral tube are very similar to those of a bar magnet.

Applications: electromagnetic cranes, electric bells, earpieces, electromagnetic relays.

2.An energized conductor is subjected to a force in a magnetic field.

Applications: electric motors, magnetoelectric meters, dynamic speakers.

3.Principle of electromagnetic induction.

Applications: Generators, microphones.

a) Electric charge. 1) Charge is a physical property of matter. A substance with an electric charge is called an "electrically charged substance".

2) Charge, which is the positive or negative charge carried by the object or the particle that constitutes the object, and the positively charged particle is called the positive charge (the symbol is "+" and the negatively charged particle is called the negative charge (the symbol is ").

3) The method of electrifying an object.

Triboelectric activation. Substance: The transfer of electrons between different objects.

Electrons are transferred from one object to another. Rubber rods rubbed with fur are negatively charged; A glass rod rubbed with silk is positively charged.

Induction of electricity. Substance: The transfer of electrons in a metallic conductor from one part of an object to another.

When a charged body is close to a conductor, the free charge in the conductor will tend to or move away from the charged body due to the mutual attraction or repulsion between the charges, so that the end of the conductor close to the charged body has a different charge, and the end away from the charged body has the same charge. This phenomenon is called electrostatic induction. The process of electrifying a metal conductor by electrostatic induction is called induced electrification.

b) Circuits. 1) Current: The free charge in the conductor is formed by regular directional motion under the action of the electric field force.

2) Current direction: The direction of positive charge directional flow is the current direction.

3) Conductor: refers to a substance with low resistivity and easy to conduct electric current. Objects that easily conduct electricity are called conductors.

4) Insulators: Substances that are not good at conducting electric current are called insulators.

5) Circuit: A conductive circuit composed of metal wires and electrical and electronic components, which is called a circuit.

6) The circuit is composed of four parts: power supply, switch, connecting wire and electrical appliance.

7) Tandem: Tandem connection is one of the basic ways to connect circuit components. The circuit components (such as resistors, capacitors, inductors, electrical appliances, etc.) are connected one by one, and the circuit composed of various electrical appliances in series is called a series circuit.

Advantages: If you want to control all appliances with a single switch in one circuit, you can use a series circuit;

Disadvantages: As long as there is a disconnection somewhere, the entire circuit becomes an open circuit. That is, the electronic components connected in series do not work properly.

8) Parallel: Parallel circuit is to make the current between the circuit elements that constitute parallel connection have more than one independent path of each other.

Features: Electrical appliances do not affect each other. The electrical appliances on one branch road are damaged, and the other branches are not affected.