Review outline for Physics and Electricity in the second semester of the second grade of junior high school, Ohm’s Law, and Electric Power. Urgent Urgent Urgent Urgent

Junior high school physics review outline (1)

Acoustics

5. All objects that are making sound are vibrating. When the vibration stops, the sound stops.

6. Sound propagates through media. The propagation speed of sound in air at 15°C is 340 meters/second, and sound cannot be transmitted in a vacuum.

Thermal Science

7. Objects The degree of heat and cold is called temperature, and the instrument that measures temperature is called a thermometer. Its principle is based on the thermal expansion and contraction properties of liquids such as mercury, alcohol, and kerosene.

8. There are two units of temperature. Two: one is the Celsius temperature, the other is the international unit, using thermodynamic temperature. The Celsius temperature is defined as follows: the temperature of the ice-water mixture is defined as 0 degrees, and the boiling water under one standard atmospheric pressure is defined as 100 degrees. Between 0 degrees and 100 degrees is divided into 100 equal parts, each divided into 1 degree Celsius. -6℃ is read as minus 6 degrees Celsius or minus 6 degrees Celsius.

9. Before using the thermometer: (1) Observe its range; (2) Recognize its minimum scale.

10. When a thermometer measures the temperature of a liquid, the correct method is: (1) The glass bulb of the thermometer must be completely immersed in the liquid being measured. ; Do not touch the bottom or wall of the container; (2) Wait for a while after the glass bulb of the thermometer is immersed in the liquid to be measured, and wait until the thermometer's indication stabilizes before taking a reading; (3) The glass bulb should remain in the liquid to be measured when reading , the line of sight is level with the upper surface of the liquid column in the thermometer.

11. The change of a substance from solid to liquid is called melting (it needs to absorb heat), and the change from liquid to solid is called solidification (it needs to release heat).

12. Solids are divided into crystals and amorphous ones. The main difference between them is that crystals have a certain melting point, while amorphous crystals do not.

13. The change of a substance from a liquid state to a gaseous state is called vaporization (endothermic), the change from gas to liquid is called liquefaction (exothermic). There are two ways of vaporization: evaporation and boiling. The difference between boiling and evaporation is: boiling occurs at a certain temperature, and occurs simultaneously on the surface and inside of the liquid A violent vaporization phenomenon, and evaporation occurs at any temperature and only occurs on the surface of a liquid.

14. To speed up the evaporation of a liquid, you can increase the temperature of the liquid and increase the density of the liquid. surface area and accelerates the air flow speed on the liquid surface.

15. The temperature when a liquid boils is called the boiling point. When boiling, it only absorbs heat and the temperature remains unchanged. Sometimes the boiling point will change appropriately because the liquid contains magnesium. Water The boiling point of is 100℃.

16. There are two ways to liquefy a gas: one is to lower the temperature, and the other is to compress the volume.

17. The change of a substance from a solid state to a gaseous state is called Vaporization (endotherm), changing from a gaseous state to a liquid state is called liquefaction (exothermic).

Optics

18. Light propagates in a straight line in a uniform medium. Light in a vacuum The speed (of air) is 3×100000000 meters/second. Shadows, solar eclipses, and lunar eclipses can all be explained by the propagation of light in a straight line in a uniform medium.

19. The law of reflection of light: reflected light In the same plane as the incident light ray and the normal line, the reflected light ray and the incident light ray are separated on both sides of the normal line, and the reflection angle is equal to the incident angle.

20. The imaging rule of a plane mirror is: (1) The image and object arrive The distance between the mirror surfaces is equal; (2) the size of the image and the object are equal; (3) the line connecting the image and the object is perpendicular to the mirror surface; (4) the resulting image is a virtual image.

21. When light is incident obliquely from one medium into another medium, the direction of propagation will generally change. This phenomenon is called refraction of light.

22. A convex lens is also called a converging lens. , such as reading glasses. Concave lenses are also called divergent lenses, such as myopia lenses.

23. The principle of the camera is: when the distance from the convex lens to the object is greater than 2 times the focal length, an inverted and reduced real image is formed.

24. The principle of a slide projector and a projector: when the distance from the object to the convex lens is between 2 times the focal length and one time the focal length, an inverted, enlarged real image is formed.

25. The principle of a magnifying glass and a microscope is : When the distance from the object to the convex lens is less than the focal length, an upright, magnified virtual image is formed.

26. Astronomical telescopes are divided into Toppler telescopes and Galilean telescopes. The principle of the Topler telescope is that the focal length of the eyepiece is small and the focal length of the objective lens is large. The objective lens presents an inverted and reduced real image almost at the focus, thus showing an inverted and reduced real image. On this basis, the eyepiece presents an enlarged virtual image, that is, f1+f2. The eyepiece of Galileo's telescope presents a magnified virtual image, namely f1-f2.

Force and motion

2. The measuring tool for length is a scale, and the main unit is meters.

3. Changes in the position of an object are called mechanical motion. The simplest mechanical motion is uniform linear motion.

4. Speed ??is a physical quantity that indicates how fast an object moves. Speed ??is equal to the distance traveled by a moving object in unit time. . Expressed by the formula: V=S/t, the main unit of speed is meters/second.

26. The amount of material contained in an object is called mass. The international main unit of mass is kilogram, and the measuring tool is a balance. .

27. How to use the balance: (1) Place the balance on a horizontal platform, place the object to be measured in the left pan, and the weight in the right pan.

28. The mass per unit volume of a certain substance is called the density of the substance. The international main unit of density is kilogram/m3, and the calculation formula is ρ=. Density is an attribute of the substance itself, which does not vary with the shape and state of the object. Changes, and does not change with the position of the object. A glass of water and a bucket of water have different masses and different volumes, but the density is the same. 1 liter = 1 decimeter 3, 1 ml = 1 cm 3, 1 g/cm 3 = 1000 kg/m3.

29. The density of water is 1.0×103 kg/m3, and its physical meaning is: the mass of 1 meter3 of water is 1.0×103 kg.

30. When using a measuring cylinder and measuring cup to measure volume readings, the line of sight should be level with the liquid surface.

31. The effect of force: first, to change the motion state of the object, and second, to deform the object. .

32. The unit of force is Newton, or Newton for short. The tool for measuring force is a dynamometer, and a spring balance is commonly used in the laboratory. The working principle of a spring balance is: the elongation of the spring is proportional to the tension. Proportional.

33. The magnitude, direction and action point of force are called the three elements of force. The method of using a line segment with an arrow to represent the three elements of force is called the graphical representation of force.

34. Force is the effect of objects on objects, and the forces between objects are mutual. The effect of force is to ① change the motion state of the object, and ② cause the object to deform.

35. The force exerted on objects due to the attraction of the earth is called gravity, and the object exerting force by gravity is the earth.

36. Gravity is proportional to mass. The relationship between them is G=mg, where g=9.8 N/kg. The point where gravity acts on an object is called the center of gravity, and the direction of gravity is vertical. Next.

37. Finding the resultant of two forces is called the synthesis of two forces. If there are two forces F1 and F2, then the resultant force when the two forces are in the same direction is F=F1+F2, and the resultant force when they are in opposite directions is F=Flarge-Fsmall.

1. All objects always remain at rest or move in a straight line at a uniform speed when not acted upon by external forces. This is Newton’s first law.

2. Objects remain at rest or move at a uniform speed. The property of the constant state of linear motion is called inertia. Therefore, Newton’s first law is also called the law of inertia. All objects have inertia.

3. Use inertia to explain: ① first describe the state of the object, ② then describe The changes that occur are ③ due to inertia, so the object still maintains its original state.

4. The conditions for the balance of two forces are: ① Two forces acting on an object, ② If they are equal in magnitude, ③ If the directions are opposite, and ④ acts on the same straight line, then the two forces are balanced. The resultant force of the two balanced forces is zero.

5. Two objects in contact with each other, when they are about to or have already become opposite When moving, a force that hinders relative movement is generated on the contact surface called friction. Friction is divided into sliding friction and rolling friction. Rolling friction is smaller than sliding friction. The size of sliding friction is related to both the size of the pressure and the contact. It is related to the roughness of the surface. We should increase beneficial friction and reduce harmful friction.

6. The force that presses vertically on the surface of an object is called pressure. The direction of pressure is perpendicular to the surface of the object. Pressure does not Must equal gravity. Pressure is equal to gravity only if the object is placed horizontally and there are no other forces.

7. The pressure on an object per unit area is called pressure. The formula for pressure is P=. The unit of pressure is "N/m2", usually called "Pa". 1 Pa=1 N/m 2. Commonly used units are hectopascal (102 pascal), kilopascal (103 pascal), and megapascal (106 pascal).

8. The liquid has pressure on the bottom and side walls of the container, and the liquid moves toward the inside. There is pressure in all directions. The pressure of a liquid increases with depth. At the same depth, the pressure of a liquid is equal in all directions; the pressure of different liquids is also related to the density. The instrument used to measure the pressure of liquids is called a pressure gauge.

9. The formula p=ρgh is only applicable to liquids. The object meaning of this formula is: the pressure of the liquid is only related to the density and depth of the liquid, and has nothing to do with the weight, volume, shape, etc. of the liquid. In the formula "h" refers to the vertical distance from a certain point in the liquid to the liquid surface. In addition, this formula is also applicable to regular, uniform and horizontally placed cubes, cylinders and other solids.

10. Top opening , the lower connected container is called a connector. Its property is: when the liquid in the connector does not flow, the liquid levels in each container always remain level. Teapots and boiler water level gauges are connectors. Ship locks use connectors It works based on the principle.

11. The air layer surrounding the earth is called the atmosphere, and the pressure of the atmosphere on objects immersed in it is called atmospheric pressure. Torricelli first measured the value of atmospheric pressure. After that In the 11th year of the 1990s, that is, in May 1654, Otto Glick, mayor of Magdeburg, Germany, conducted the famous Magdeburg Hemisphere Experiment, which proved the existence of atmospheric pressure.

12. The atmospheric pressure equal to 760 mm of mercury is called a standard atmospheric pressure. 1 standard atmosphere ≈ 1.01×105 Pa (P=ρgh =13.6×103 kg/m3×9.8 N/kg×0.76 m≈1.01×105 Pa). 1 standard Atmospheric pressure can support a water column of about 10.3 meters high and a kerosene column of about 12.9 meters high.

13. Atmospheric pressure decreases as altitude increases. The instrument for measuring atmospheric pressure is called a barometer. The boiling point of a liquid It is related to air pressure. The boiling point of all liquids decreases when the air pressure decreases and increases when the air pressure increases. A pressure cooker is required for cooking on high mountains.

14. Piston water pumps, centrifugal water pumps, and pen suction pumps Ink feeding, etc. all work based on the principle of atmospheric pressure.

15. An object immersed in a liquid is subject to an upward and downward pressure difference. This is the buoyancy force of the liquid on the object (F float = F down —F up). This is the reason for the buoyancy force. The buoyancy force is always vertical and upward. F floating G objects sink; F floating G objects float; when objects are suspended or floating, there are F floating = G objects, but both There is a difference (V row is different).

16. Archimedes' principle: An object immersed in a liquid experiences an upward buoyant force, and the magnitude of the buoyant force is equal to the gravity of the liquid it displaces. The formula is F Float = G row = ρ liquid gV row. Archimedes' principle also applies to gases. Substances that are denser than water (such as iron, etc.) are usually made hollow to float on the water. Ships, submarines, balloons and airships etc. all make use of buoyancy.

17. If a hard rod can rotate around a fixed point under the action of force, this hard rod is called a lever. Distinguish the fulcrum, power, resistance and power of the lever. arm, resistance arm.

18. The balance condition of the lever is: power × power arm = resistance × resistance arm formula is F1L1 = F2L2 or =

19. There are three types of levers Situation: ① The power arm is larger than the resistance arm, that is, L1 L2, when balanced, F1 F2, which is a labor-saving lever; ② The power arm is smaller than the resistance arm, that is, L1 L2, when balanced, F1 F2, which is a labor-saving lever; ③ The power arm is equal to the resistance arm, that is L1 = L2, when balanced, F1 = F2, which is neither labor-saving nor labor-intensive. It is an equal-arm lever, and its specific application is a balance.

20. Many scales for weighing mass, such as steelyard scales and case scales, are It is made based on the principle of leverage.

21. There are two types of pulleys: fixed pulleys and movable pulleys. The fixed pulley is essentially an equal-arm lever, so the fixed pulley is not labor-saving, but it can change the direction of the force; the movable pulley is essentially a The power arm is twice the lever of the resistance arm, so the moving pulley can save half the force, but it cannot change the direction of the force.

22. Use the pulley

When pulling a pulley, the pulley uses several sections of rope to hang the object. The force used to lift the object is a fraction of the weight of the object. And when the object rises by "h", the pulling force moves "nh", where "n" is the number of rope segments. .

23. The work mentioned in mechanics includes two necessary factors: one is the force acting on the object, and the other is the distance traveled by the object in the direction of the force. Work is equal to the distance between the force and the object. The product of the distance traveled in the direction of the force. The formula is W=FS. The unit of work is joule, 1 joule = 1 N·m.

24. Using any machinery does not save work. This conclusion is called The principle of work. Applying it to an incline is: FL=Gh. or: F= G.

25. The work done to overcome useful resistance is called useful work, and the work done to overcome useless resistance is called extra Work. Useful work plus extra work equals total work. The ratio of useful work to total work is called mechanical efficiency. The formula is η=. It is generally expressed as a percentage. Mechanical efficiency is always less than 1.

26. The work done per unit time is called power. The formula is P=. The unit is watt, 1 watt = 1 joule/second, 1 kilowatt = 1000 watts. In addition

, P= = = F·v, formula description: When the vehicle goes uphill, since the power (P) is constant and the force (F) increases, the speed (v) must decrease.

Junior high school physics review Outline (2)

Mechanical Energy Molecular Kinetic Theory Internal Energy

1. If an object can do work, we say it has functional energy. The energy an object possesses due to motion is called kinetic energy. Kinetic energy It is related to the speed and mass of the object. The greater the speed and mass of the moving object, the greater the kinetic energy. All moving objects have kinetic energy.

2. Potential energy is divided into gravitational potential energy and elastic potential energy. Lift high The energy possessed by an object is called gravitational potential energy. The greater the mass of an object and the higher it is lifted, the greater the gravitational potential energy. The energy possessed by an object that undergoes elastic deformation is called elastic potential energy. The greater the elastic deformation of an object, the greater its elastic potential energy. Large.

3. Kinetic energy and potential energy are collectively called mechanical energy. The units of energy, work, and heat are all joules. Kinetic energy and potential energy can be converted into each other. Basic knowledge of molecular kinetic theory: ① Matter is composed of molecules, and molecules Extremely tiny. ② Molecules make endless and irregular motion. ③ There are mutual attraction and repulsion forces between molecules.

4. The phenomenon that different substances enter each other when they come into contact is called Diffusion. The phenomenon of diffusion illustrates the never-ending irregular motion of molecules.

5. The sum of the kinetic energy and molecular potential energy of all molecules in an object making irregular movements is called the internal energy of the object. All objects There is internal energy. The internal energy of an object is related to the temperature. The higher the temperature, the more intense the irregular motion of the molecules inside the object, and the greater the internal energy of the object. The higher the temperature, the faster the diffusion.

6. The irregular motion of a large number of molecules in an object is called thermal motion, and the internal energy is also called heat. The two methods of changing the internal energy of an object are: work and heat transfer. The internal energy of an object increases when it does work on the object, and decreases when the object does work on the outside. Small; when an object absorbs heat, the internal energy of the object increases; when the object emits heat to the outside, the internal energy of the object decreases.

7. The temperature of a certain substance per unit mass increases (or decreases) by 1℃ ( or released) is called the specific heat capacity of this substance, referred to as specific heat. The unit of specific heat is JJ/(kg·℃). The specific heat of water is 4.2×103 J/(KG·℃). Its physical meaning is : When the temperature of 1 kilogram of water increases (or decreases) by 1°C, the heat absorbed (or released) is 4.2×103J. The specific heat of water is the largest. Therefore, the temperature changes in coastal areas are not as significant as inland.

8. Q absorbs = cm(t - t0); t).

9. Energy neither disappears nor is created. It only transforms from one form into other forms, or transfers from one object to another. During the process, the total amount of energy remains unchanged. This law is called the law of conservation of energy. In the utilization of internal energy, internal energy can be used to heat and internal energy can be used to do work.

10. 1 kilogram of a certain The heat released by the complete combustion of a fuel is called the calorific value of the fuel. The unit of calorific value is: J/kg. The calorific value (maximum) of hydrogen is 1.4 × 108 J/kg, and its physical meaning is: 1 kg The heat released by the complete combustion of hydrogen is 1.4 ×108 joules.

Electricity

1. When a rubbed object has the property of attracting light and small objects, it is said that the object is charged. Use The method of friction to charge objects is called triboelectricity.

2. There are two kinds of charges in nature. Glass rubbed with silk is positively charged; rubber rod rubbed with fur is negatively charged. Same charges interact with each other. Repulsion, different charges attract each other.

3. The amount of charge is called electric charge. The symbol of charge is "Q", the unit is Coulomb, or Coulomb for short, and it is represented by the symbol "C".

4. The reason for frictional electrification is the transfer of charge. The electrons are negatively charged. The lost electrons are positively charged; the gained electrons are negatively charged.

5. The directional movement of charges forms an electric current. Move the positive charges in the direction stipulated as electric

The direction of the flow. A device that can provide continuous power supply is called a power supply. Dry batteries and lead-acid batteries are both power supplies. The function of a DC power supply is to continuously gather the positive electrode inside the power supply. Positive charge, the negative electrode collects negative charge. When dry batteries and batteries provide power to the outside world, chemical energy is converted into electrical energy.

6. Objects that easily conduct electricity are called conductors. Metal, graphite, human body, earth, as well as acids, alkalis, Salt aqueous solutions, etc. are all conductors; objects that are not easy to conduct electricity are called insulators. Rubber, glass, ceramics, plastics, oil, etc. are insulators. There is no absolute boundary between conductors and insulators. Metal conducts electricity by free electrons. < /p>

7. The current path formed by connecting power supplies, electrical appliances, switches, etc. with wires is called a circuit. A connected circuit is an electrical path; a disconnected circuit is electrically open; a wire is directly connected without using electrical appliances. A circuit connected at both ends of a power supply is called a short circuit. A diagram that uses symbols to represent the connections of a circuit is called a circuit diagram. A circuit formed by connecting components one by one in sequence is called a series circuit. A circuit formed by connecting components in parallel is called a parallel circuit.

< p>8. The current intensity is equal to the amount of electricity passing through the cross-section of the conductor in 1 second. "I" represents the current, "Q" represents the electricity, and "t" represents the time, then I=. 1A=1 bank/second. 1A (A) = 1000 milliamps (mA); 1 milliampere (mA) = 1000 microamps (μA);

9. The instrument that measures current is called an ammeter. There are generally two ammeters used in laboratories. Measuring range and three binding posts, the two measuring ranges are 0 to 0.6 A and 0 to 3 A respectively; when connecting 0 to 0.6 A, each large division is 0.2 A and each small division is 0.02 A; when connecting 0 to 3 Each large grid of ampere-hour is 1 A and each small grid is 0.1 A.

10. When using an ammeter: ① The ammeter must be connected in series in the circuit; ② The "+" and "-" terminal connections must be Correct; ③ The measured current should not exceed the range of the ammeter; ④ It is absolutely not allowed to connect the ammeter directly to the two poles of the power supply without using electrical appliances.

11. Voltage causes current to form in the circuit. Use symbols for voltage "U" means, the unit is volt, represented by "V". 1 kilovolt (kV) = 1000 volts (V); 1 volt (V) = 1000 millivolts (mV); 1 millivolt (mV) = 1000 microvolts Volt (μV). The voltage of a dry battery is 1.5 volts, the silver oxide battery used in electronic watches is also 1.5 volts each, and the lead-acid battery is 2 volts each. The voltage of the household circuit is 220 volts, and the safe voltage for the human body is no more than 36 volts. .

12. The instrument that measures voltage is called a voltmeter. Voltmeters used in laboratories generally have two ranges and three binding posts. The two ranges are 0 to 3 volts and 0 to 15 volts respectively; When connected to 0 to 3 volts, each large grid is 1 volt and each small grid is 0.1 volt; when connected to 0 to 15 volts, each large grid is 5 volts and each small grid is 0.5 volts.

13. Voltage When using the meter: ① The current and voltage meter must be connected in parallel in the circuit; ② The "+" and "-" terminal connections must be correct; ③ The measured voltage should not exceed the range of the voltmeter.

14. Conductor The resistance to current is called resistance. Resistance is a property of the conductor itself. Its size determines the material, length and cross-sectional area of ??the conductor. The symbol of resistance is "R", the unit is "ohm", and the unit symbol is "Ω ”. 1 megohm (MΩ) = 1000 kiloohms (kΩ); 1 kiloohm (kΩ) = 1000 ohms (Ω).

15. The function of a rheostat is to change the resistance of the resistance line in the circuit. The length can gradually change the resistance, thereby gradually changing the current. To achieve the purpose of controlling the circuit.

16. The current in a conductor is proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor. This conclusion It's called Ohm's law. The formula is: I= .

17. The work done by the current on a certain circuit is equal to the product of the voltage at both ends of the circuit, the current in the circuit and the energization time. The formula is W=UIt. The unit of electrical power is "joule". In addition, 1 degree = 1 kilowatt hour = 3.6 × 106 joules, "degree" is also the unit of electrical power.

18. Current in units The work done within the time is called electrical power. The formula is P=UI. The voltage when the electrical appliance is working normally is called the rated voltage, and the power of the electrical appliance at the rated voltage is called the rated power. For example, "PZ220V 100W" means the rated voltage

It is 220 volts, and the rated power is 100 watts.

19. The heat generated by the current passing through the conductor is proportional to the square of the current, the resistance of the conductor, and the power-on time. This conclusion is called Joule's law. The formula is Q=I2Rt. The unit of heat is "joule". An electric heater is a device that uses electricity to heat. Such as electric stoves, electric soldering irons, electric irons, etc.

20. Two parts of household circuits There are two wires, one is called the live wire and the other is called the neutral wire. There is a voltage of 220 volts between the live wire and the neutral wire, and the neutral wire is grounded. The instrument that measures how much electric energy is consumed in a household circuit within a certain period of time is called an energy meter. Its The unit is "degree".

21. The fuse is made of lead-antimony alloy with high resistivity and low melting point. Its function is to automatically cut off the circuit before the current in the circuit reaches a dangerous level. When replacing the fuse, you should choose a fuse with a rated current equal to or slightly larger than the current during normal operation. Never use copper wire to replace the fuse.

22. The reasons for excessive current in the circuit are: ① short circuit; ②The total power of the electrical appliances is too large. The sockets are divided into two-hole sockets and three-hole sockets.

23. The use of the electric test pen is: touch the metal body at the end of the pen with your hand, the tip of the pen touches the wire, and the neon tube emits light The live wire is the live wire, and the neutral wire is the neutral wire.

24. The principle of safe use of electricity is: do not touch low-voltage charged objects; do not approach high-voltage charged objects. Be especially vigilant about uncharged objects being charged. Objects that should be insulated conduct electricity.

Electromagnetism

1. Permanent magnets include artificial magnets and natural magnets. A bar magnet or magnetic needle that rotates freely in a horizontal plane will always One end points to the south pole (called the South Pole), and the other end points to the north (called the North Pole). Magnetic poles with the same name repel each other, and magnetic poles with different names attract each other. The process by which non-magnetic substances become magnetized is called magnetization. The magnetization of an iron rod disappears easily after being magnetized, and is called a soft magnet. ; The magnetization of the steel rod is not easy to disappear after magnetization, so it is called a hard magnet.

2. There is a magnetic field in the space around the magnet. The basic property of the magnetic field is to produce magnetic force on the magnet placed in it, so a small magnetic needle can be used Identify whether there is a magnetic field in a certain space.

3. In order to describe the magnetic field visually, people introduce magnetic field lines (which do not actually exist). (The model method is adopted) The density of the magnetic field lines represents the strength of the magnetic field at that location, and the direction of the magnetic field lines (that is, the tangent direction) represents the direction of the magnetic field at that location. Outside the magnet, the magnetic field lines start from the North Pole and return to the South Pole, and inside the magnet, the magnetic field lines point from the South Pole to the North Pole. Magnetic field lines are all closed curves.

4. You can use Ampere's rule (right-hand spiral rule: Hold the wire in your right hand so that the direction of your straight thumb is consistent with the direction of the current, then the direction of the bent four fingers is the direction of the magnetic field) to determine the direction of the magnetic field generated by the current. For a energized solenoid, use the circling direction of the four fingers of your right hand to indicate the direction of the current on the solenoid. The thumb pointing is the N pole of the energized solenoid.

5． Electromagnets have many advantages over permanent magnets. They can control the presence, strength, and direction of the magnetic field by adjusting the presence, strength, and direction of the current. Electromagnetic relays (electric bells) made of electromagnets are often used in automatic control and remote control.

6． A current-carrying conductor will experience a force in a magnetic field, and the direction of the force is related to the direction of the current and the direction of the magnetic field lines.

7. DC motors are made by using an energized coil to rotate under the action of force in a magnetic field. In this process, electrical energy is converted into mechanical energy. In a DC motor, a commutator is used to change the direction of the current in the coil, so that the coil continues to rotate in the same direction under the action of the magnetic field force.

8． When a part of a conductor in a closed loop moves to cut magnetic field lines in a magnetic field, an induced current will be generated in the conductor, which is the phenomenon of electromagnetic induction. The conditions for generating induced current are: first, the circuit is closed; second, the conductor moves to "cut" the magnetic field lines, that is, the direction of movement of the conductor cannot be parallel to the magnetic field lines.

9． The generator is made by using the principle of generating induced current when a closed coil cuts magnetic field lines in a magnetic field and rotates. It is a device that converts mechanical energy into electrical energy.

10. Batteries are divided into chemical batteries (the positive electrode is a copper-capped carbon rod), fruit batteries, voltaic batteries (a milestone and a real battery), and storage batteries (containing lead and sulfuric acid, which are highly polluting). ), solar cells (pollution-free, using renewable energy), fuel cells

Power plants generate electricity in the following ways: thermal power generation, hydropower generation, wind power generation, nuclear power generation, tidal power generation, etc.

This is a junior high school physics syllabus, I hope it can help you

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