Physics concept of junior three

Physics concept of junior three

A review of the concept formula in the middle of Junior Physics
11.1 simple machines (Part 3, 20-31)
1. Lever: a hard rod that can be around a fixed point under the action of the lever is called lever
2. The five elements of leverage are:
3. The balance of lever: (1) the lever is in the state or makes the slow is called the lever balance
4. Conditions of lever balance: the formula is as follows:
5. Three levers:
(1) Labor saving lever: L1, L2, F1, F2 when balanced
(2) Hard lever: L1, L2, balance F1, F2. Characteristic is, but save.)
(3) Equal arm lever: L1, L2, F1, F2 when balancing
6. Fixed pulley features: No, but it can change the direction of the wheel
7. Moving pulley features: labor saving, but can not change the direction of power, it costs distance
8. Balance, movable pulley, fixed pulley, automobile brake, foot collapse plate of sewing machine, crane boom, iron scissors, barber scissors, cloth scissors, guillotine, driver, fishing rod, among them, labor-saving lever and equal arm lever
9. Pulley block: when using the pulley block, the pulley block uses several sections of rope to hang the object, and the force used to lift the object is a fraction of the weight of the object
11.2 work and power mechanical efficiency
1. The two essential factors of merit: one is the quality of work; the other is the quality of work
2. Calculation of work: work (W) is equal to the product of (f) and (s) in the direction of force
(merit = ×)
3. Formula of work:; unit: W →; F →; s →. (1 joule = 1)
4. Principle of work: when using machinery, the work done by people is not less than the work done directly by hand without machinery, that is to say, it is impossible to use any machinery
5. Mechanical efficiency: the ratio of to is called mechanical efficiency
6. In the experiment of measuring the mechanical efficiency of pulley block, the experimental principle is
In addition to the hook code, iron frame platform and thin wire, the factors that affect the mechanical efficiency of the pulley block are: methods to improve the mechanical efficiency of the pulley block are: the height of the object to be lifted, and whether the winding method of the rope affects the mechanical efficiency?
7. Power (P): is called power. Calculation formula: or. Unit: P →; w →; t →. (1 watt = 1 kW = 1 000 Watt)
8. Power is the speed of an object
12.1 mechanical energy (part three 48-55)
1. If an object can do work, it will have
2. Kinetic energy: the energy that an object has due to its motion is called kinetic energy. The larger the moving object is, the greater the kinetic energy is
3. Potential energy is divided into sum
4. Gravitational potential energy: the energy possessed by an object due to its gravity. The larger the object is, the more it is lifted, the greater the gravitational potential energy
5. Elastic potential energy: the energy of an object due to its occurrence. The larger the size of an object, the greater its elastic potential energy
6. Mechanical energy: sum. (mechanical energy = kinetic energy + potential energy) the unit of energy is:
7. Kinetic energy and potential energy can interact with each other
8. When a satellite rotates around the earth, its gravitational potential energy, kinetic energy and velocity will change from perigee to apogee
11. In nature, the mechanical energy that can be used by human beings are water energy and wind energy
12. Conversion and conservation of mechanical energy: in the process of mutual conversion of kinetic energy and potential energy, if there is no friction and other resistance, then the total amount of mechanical energy
12.2 specific heat internal energy
1. Internal energy: the sum of the irregular motion of all molecules in an object is called internal energy
2. The internal energy of an object is related to: the higher the object is, the faster the molecule is, and the higher the internal energy is
3. There are two ways to change the internal energy of an object and, these two ways are effective to change the internal energy of an object
4. External work, internal energy; external work, internal energy
5. When the temperature rises, the body absorbs the internal energy; when the temperature drops, the body releases the internal energy
6. Heat (q): in the process of heat transfer, the amount of heat transferred is called heat. (it is wrong to say that an object contains heat). The condition of heat transfer is that there is a gap between the object or different parts of the object
7. Specific heat capacity (c): the specific heat capacity of a substance that is absorbed (or released) when its temperature rises (or falls). The unit of specific heat capacity is
8. Specific heat capacity is an attribute of matter. It doesn't change with the change of temperature. As long as the matter is the same and the state is fixed, the specific heat capacity will change
9. The specific heat capacity of water is: C = J / (kg &; 0C), which means that the heat absorbed (or released) is 4.2 × 103J when the temperature of water increases (or decreases) 10C per kilogram
10. Calculation of heat: Q absorption = = cm △ t (Q absorption is absorption, unit is; C is object, unit is:; m is; t0 is; t is
Q =, where to-t = Δ t is the temperature of the substance
11. Calorific value (q): the heat released by the combustion of a certain fuel, which is called calorific value
12. Calculation of heat release from fuel combustion: q = MQ; (q is, unit is; q is, unit is
13. A heat engine is a machine that converts the energy obtained from fuel combustion into energy. It can be converted into energy in the compression stroke and into energy in the work stroke
14. A working cycle of gasoline engine consists of four strokes, i.e., the piston moves up and down times, the crankshaft rotates, and the external work is done times
15. In a heat engine, the ratio of the energy used to do work to the energy obtained is called the efficiency of the heat engine. The total efficiency of the heat engine is 1
13.1 circuit current and voltage
1. Power supply: a device that can provide power supply. The function of power supply is to make the positive pole and the negative pole gather continuously inside the power supply. The current outside the power supply flows from the current direction
2. Power supply is to convert energy into energy. For example, dry battery is to convert energy into energy. Generator is to convert energy into energy
3. When using electrical energy to work, convert the energy into other forms of energy
4. The circuit is composed of,, and
5. There are three states in a circuit: (1) the circuit with path is called path; (2) the circuit with open circuit is called open circuit; (3) the circuit with short circuit is called short circuit
6. Circuit diagram: the diagram that indicates the physical connection of circuit components with circuit component symbols
7. Series connection: connecting electrical appliances is called series connection
8. Parallel connection: connecting the ground of electrical appliances is called parallel connection
9. It is used to indicate the size of current in physics. The unit of current I is: international unit is:; the common units are: Ma, micro A. 1 a = ma = micro A. in table lamp, color TV, semiconductor radio, electric fan, refrigerator, electric iron and other household appliances, the maximum current is, and the minimum current is
10. The instrument for measuring current is: its use rules are: ① the ammeter should be connected in the circuit; ② the connection method of the terminal should be correct, so that the current flows in and out from the terminal; ③ the measured current should not exceed the current of the ammeter; when the measured current is unknown, the method should be used to select the range. ④ it is absolutely not allowed to connect the ammeter to the circuit without using electrical appliances
11. There are two ranges of ammeters commonly used in the laboratory: ① 0-0.6 a, the current value of each cell is a; ② 0-3 a, the current value of each cell is a
12. Voltage (U): voltage is the cause of the formation of voltage in the circuit, which is the device to provide voltage
13. The unit of voltage U is: international unit is:; common units are: kilovolt (kV), millivolt (MV), Microvolt (& micro; V)
1 kV = v = MV = microvolt
14. The instrument for measuring voltage is: its use rules are: ① the voltmeter should be in the circuit; ② the connection method of the terminal should be correct, so that the current enters from the terminal and goes out from the terminal; ③ the measured voltage should not exceed the value of the voltmeter;
15. There are two ranges of voltmeters commonly used in the laboratory: ① 0-3v, the voltage value of each cell is V; ② 0-15v, the voltage value of each cell is v
16. Memorized voltage value:
① The voltage of one dry battery is V; the voltage of one lead-acid battery is V; the voltage of home lighting is V; the voltage of safety is V; the voltage of industrial lighting is v
Ohm's law of resistance
1. Resistance (R): the effect of conductor on current
2. Unit of resistance (R): international unit:; commonly used units are: megohm (m Ω), kiloohm (K Ω)
One megaohm = kiloohm; one kiloohm = ohm
3. Study the factors that affect the resistance: (1) when the length and cross-sectional area of conductors are fixed, the resistance is generally different. (2) when the sum of conductors is the same, the longer the conductor is, the higher the resistance is. (3) when the sum of conductors is the same, the larger the cross-sectional area of conductor is, and the higher the resistance is. (4) the resistance of conductor is also related, for most conductors, the higher the resistance is
4. Factors determining the size of the resistance: the resistance of a conductor is a property of the conductor itself, and its size depends on:,,, and (resistance is related to the voltage applied at both ends of the conductor and the current passing through)
Rubber, graphite, ceramics, human body, plastic, earth, water solution of pure water, acid, alkali, salt, glass, air, oil. Among them, the conductor is made of carbon
6. There is no absolute boundary between conductor and insulator, and they can transform into each other under certain conditions. Glass at room temperature is, while glass in state is
Semiconductor: the object between conductive conductor and insulator
8. Superconductor: when the temperature drops to a very low level, some substances will disappear completely. The object that occurs this phenomenon is called superconductor (with or without) resistance
9. Rheostat: (sliding rheostat and rheostat box)
(1) Sliding rheostat:
① Principle: change the resistance wire in the circuit to change the resistance
② Function: by changing the access circuit to change the circuit
③ Name plate: if a sliding rheostat is marked with "50 Ω 2A", it means:
④ Correct use: A should be connected in the circuit; B wiring should be "one up and one down"; C should adjust the resistance to the place before power on
(2) Rheostat box: it is a rheostat that can be expressed
10. Ohm's Law: 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
11. Formula: () where unit: I →; u →; R →
13. Application of Ohm's law
① The same resistance, constant, resistance and current and voltage. When the voltage applied to both ends of the resistance increases, the current through the resistance will (fill in "larger, constant, smaller") (r = u / I)
② When the voltage is constant, the larger the resistance is, the more current will flow. (I = u / R)
③ When the current is constant, the greater the resistance, the higher the voltage at both ends of the resistance. (U = IR)
14. The series connection of resistance has the following characteristics: (R1, R2 series connection)
① Current: (the current is equal everywhere in a series circuit)
② Voltage: (the total voltage is equal to the sum of the voltages of each part)
③ Resistance: (the total resistance is equal to the sum of the resistances) if n resistances with the same resistance value are connected in series, there is r total resistance=
④ Partial pressure: U1: U2 =;
⑤ Proportional relationship: current: I1 ∶ I2=
The parallel connection of resistance has the following characteristics: (refers to R1, R2 parallel connection)
① Current: (the main current is equal to the sum of the branch currents