physics
Physical quantity unit formula
Name symbol name symbol
Mass m kg kg m=pv
Temperature t celsius c
Speed v m/sec m/sec v = sec/sec
Density p kg/m? kg/m？ p=m/v
Force (gravity) f Newton (cattle) N G=mg
Pressure p Pascal (Pa) Pa P=F/S
Work w joule (coke) J W=Fs
Power p watt (watt) w P=W/t
Current I Ampere (A) A I = U/R.
Voltage u volts (volts) V U=IR.
Resistance r ohm (ohm) r = u/i.
Electric power watt Joule (joule) watt =UIt
Electric power p watt (W) w P=W/t=UI.
Heat q joule (coke) j q = cm (t-t)
Specific heat c coke/(kg c) j/ (kg c)
The speed of light in vacuum is 3x108m/s.
9.8 N/kg
15 C the speed of sound in the air is 340 m/s.
Safe voltage is not higher than 36 volts.
An overview of the basic concepts of junior high school physics
I. Measurement
1. length l: main unit: meter; Measuring tool: scale; When measuring, it is necessary to estimate the next bit of the minimum scale; The unit of light years is the unit of length.
Time t: primary unit: seconds; Measuring tools: clocks and watches; Stopwatch is used in the laboratory. 1 = 3600 seconds, 1 second = 1000 milliseconds.
3. mass m: the amount of matter contained in an object is called mass. Main unit: kg; Measuring tool: scale; Tray balance for laboratory use.
Second, the mechanical movement
1. Mechanical motion: the motion of changing the position of an object.
Reference: To judge the motion of an object, another object must be selected as the standard, and the object selected as the standard is called the reference.
3. Uniform linear motion:
① Two methods to compare the speed of movement: A Compare the distance traveled in the same time. Compare the time required to drive the same distance.
② formula:1m/s = 3.6km/h.
Third, force.
Force F: Force is the action of an object on an object. The forces between objects always interact.
Unit of force: Newton (n). Instruments for measuring force: dynamometer; Spring scales are used in laboratories.
The function of force: to deform an object or change its motion state.
The change of the motion state of an object refers to the change of the speed or direction of the object.
The three elements of force: the size, direction and action point of force are called the three elements of force.
The diagram of force should be proportional; Schematic diagram of forces, not to scale.
3. Gravity G: the force exerted on an object due to the attraction of the earth. Direction: vertical downward.
The relationship between gravity and mass: g = mg m = g/g.
G=9.8 N/kg. Reading: 9.8 N/kg, that is to say, the weight of an object with a mass of 1 kg is 9.8 N. ..
Center of gravity: the point of action of gravity is called the center of gravity of an object. The center of gravity of a regular object is in the geometric center of the object.
2. Two-force balance condition: acting on the same object; These two forces are equal in magnitude and opposite in direction; Linear motion.
Under the balance of two forces, an object can be at rest or move in a straight line at a uniform speed.
The equilibrium state of an object means that the object is in a state of static or uniform linear motion. The resultant force of external forces on an object in equilibrium is zero.
5. Synthesis of two forces on the same line: same direction: resultant force f = f1+F2; The direction of resultant force is the same as that of F 1 and F2;
Opposite directions: the resultant force F=F 1-F2, and the resultant force direction is the same as the strong force direction.
Under the same conditions, rolling friction is much smaller than sliding friction.
Sliding friction is related to positive pressure, material characteristics and contact surface roughness. Sliding friction, rolling friction and static friction.
7. Newton's first law, also known as the law of inertia, means that all objects are always in a state of static or uniform linear motion when they are not affected by external forces. Inertia: The property that an object maintains its original static or uniform linear motion is called inertia.
Fourth, density.
⒈ Density ρ: the mass per unit volume of a substance, and density is a characteristic of the substance.
Formula: m=ρV International unit: kg/m3, common unit: g/cm3,
Relationship:1g/cm3 =1x103kg/m3; ρ water =/kloc-0 /×103kg/m3;
Reading: per cubic meter 103kg, which means that the mass of 1 cubic meter of water is 103kg.
1. Density measurement: measure the mass with a pallet balance, and measure the volume of solid or liquid with a measuring cylinder.
Area unit conversion:
1 cm2 = 1× 10-4 m2，
1 mm2 = 1× 10-6mm 2。
Verb (short for verb) pressure
1. pressure p: the pressure per unit area of an object is called pressure.
Pressure f: the force acting vertically on the surface of an object, in N. ..
The function of pressure is expressed by pressure, which is related to pressure and stress area.
Pressure unit: n/m2; Technical name: Pascal (Pa)
Formula: F=PS S: stress area, the common part of two objects in contact; Unit: square meters.
Methods of changing pressure: ① reducing pressure or increasing stress area can reduce pressure; ② Increasing the pressure or decreasing the stress area can increase the pressure.
1. liquid internal pressure: measure the liquid internal pressure: use a liquid manometer (u-tube manometer).
Reason: Because the liquid has gravity, it exerts pressure on the bottom of the container; Due to the fluidity of the liquid, pressure is generated on the wall of the device.
Law: ① At the same depth, the pressure in all directions is equal; ② The greater the depth, the greater the pressure; ③ Different liquids at the same depth, the higher the liquid density, the greater the pressure. [Depth h, the vertical height from the liquid surface to a certain point of the liquid. ]
Formula: p = P=ρgh h: unit: meter; ρ: kg/m3; G=9.8 N/kg.
13. Atmospheric pressure: gravity produces atmospheric pressure, which proves the existence of atmospheric pressure and is very large. It was the Madeborg Hemisphere Experiment and Torricelli (an Italian scientist) who measured the atmospheric pressure. After the Torricelli tube is tilted, the height of the mercury column remains unchanged and the length becomes longer.
1 standard atmospheric pressure = 76 cm mercury column height =1.01×105pa =10.336m water column height.
Instruments for measuring atmospheric pressure: barometer (mercury barometer, box barometer).
The law of atmospheric pressure changing with altitude: the higher the altitude, the smaller the pressure, that is, the lower the boiling point with the elevation.
Six, buoyancy
1. Buoyancy and its causes: An object immersed in liquid (or gas) is called buoyancy when it is pushed upward by liquid (or gas). Direction: vertically upward; Cause: the pressure difference between liquid and object.
2. Archimedes principle: An object immersed in a liquid is subjected to upward buoyancy, and the buoyancy is equal to the gravity when the object displaces the liquid.
That is, f float = G liquid discharge = ρ liquid gV discharge. (Line V represents the volume of liquid discharged by the object)
3. Buoyancy calculation formula: F float = G-T = ρ gV drainage = F up-down pressure difference.
4. When the object floats: F float = G object and ρ object.
When the object floats: f floats >; G and ρ < ρ liquid when the object sinks: ρ liquid when F floats.
Seven, simple machinery
1. Lever balance condition: f 1L 1 = f2l2. Force arm: the vertical distance from the fulcrum to the line of force action.
The purpose of keeping the lever in the water position by adjusting the nuts at both ends of the lever is to facilitate the direct measurement of the length of the power arm and the resistance arm.
Crown block: equivalent to an arm. It can't save energy, but it can change the direction of force.
Moving pulley: it is equivalent to a lever with twice the power arm as the resistance arm, which can save half of the force, but cannot change the direction of the force.
Work: two necessary factors: ① the force acting on the object; ② The passing distance of the object in the direction of force. W = W unit =FS Work: Joule.
3. Power: the work done by an object in unit time. A physical quantity indicating the speed at which an object does work, that is, an object with high power does work quickly.
W = unit W = Pt P:watt；; Unit of w: joule; Unit of t: seconds.
Eight, light
1. Linear propagation of light: Light propagates linearly in the same homogeneous medium. Aperture imaging, shadow and spot are all linear propagation phenomena of light.
The maximum speed of light in vacuum is 3x108m/s = 3x105km/s.
Law of light reflection: one side, two sides and three dimensions. The angle between the incident light and the normal is the incident angle. The angle between the reflected light and the normal is the reflection angle.
Imaging characteristics of plane mirror: virtual image, equal size, equal distance and mirror symmetry. The reflection of objects in water is the reflection of virtual images and light.
3. The phenomenon and law of light refraction: Seeing the virtual image of chopsticks and fish in water is the phenomenon of light refraction.
Convex lens has the function of converging light, while concave lens has the function of diverging light. The law of refraction of light: one side, two sides, three sides, big four empty.
3. The law of convex lens imaging: [When u = f, no imaging; When U=2f, V=2f becomes a real image with inverted size]
Properties of object distance U image distance V image Application of light path diagram
U & gt2f f<v & lt2f Inverted Micro Reality Camera
F<u & lt2f v & gt2f Inverted Amplification Real Slide Projector
U< magnifying glass
⒌ Convex lens imaging experiment: Put the candle, convex lens and light screen on the optical bench in turn, so that the centers of the candle flame, convex lens and light screen are at the same height.
Nine, thermal energy:
1. temperature t: indicates the degree of heat and cold of the object. It is a state quantity.
Principle of common thermometer: According to the characteristics of liquid expanding when heated and contracting when cooled.
The differences between thermometers and thermometers are: ① range, ② minimum scale, ③ glass bulb, curved thin tube and ④ usage.
2. Heat transfer conditions: temperature difference. Heat: the heat absorbed or released by an object during heat transfer. This is a process quantity.
There are three ways of heat transfer: conduction (heat is transferred along an object), convection (heat is realized by the flow of liquid or gas) and radiation (heat is directly emitted from a high-temperature object).
3. Vaporization: the phenomenon that a substance changes from a liquid state to a gas state. Mode: evaporation and boiling, evaporation should absorb heat.
The factors that affect the evaporation rate are: ① liquid temperature, ② liquid surface area and ③ air flow on the liquid surface. Evaporation has a cooling effect.
1. specific heat capacity c: the heat absorbed by a substance with unit mass when the temperature rises by 65438 0℃ is called the specific heat capacity of the substance.
Specific heat capacity is one of the characteristics of matter, and the unit is coke/(kg℃). The specific heat capacity of water in common substances is the largest.
C water = 4.2× 103 joules/(kg℃), reading: 4.2× 103 joules per kg℃.
Physical meaning: The mass of water is 1 kg, the temperature of water rises 1℃, and the absorbed heat is 4.2× 103 Joule.
⒌ Thermal calculation: Q discharge = cm ⊿ t q decrease and intake = cm ⊿ t liter.
Q is directly proportional to c, m and ⊿t, and inversely proportional to c, m and ⊿ t ⊿ t = q/cm.
6. Internal energy: the sum of kinetic energy and molecular potential energy of all molecules in an object. All objects have internal energy. Internal energy unit: Joule
The internal energy of an object is related to its temperature. When the temperature of an object increases, the internal energy increases; When the temperature decreases, the internal energy decreases.
Methods of changing the internal energy of an object: work and heat transfer (equivalent to changing the internal energy of an object)
7. Law of energy transformation and conservation: energy will neither be generated out of thin air nor disappear out of thin air, but will only be transformed from one form to another, or transferred from one object to another, and the total amount of energy will remain unchanged.
Circuit
The circuit consists of power supply, electric key, electrical appliances, wires and other components. In order to have a continuous current in the circuit, there must be a power supply in the circuit and the circuit should be closed. The circuit has the phenomena of access, open circuit (open circuit), short circuit of power supply and electrical appliances.
2. A substance that conducts electricity easily is called a conductor. Such as aqueous solutions of metals, acids, bases and salts. Substances that do not conduct electricity easily are called insulators. Such as wood and glass.
Under certain conditions, an insulator can become a conductor.
3. Identification of series-parallel circuits: series: current does not bifurcate, parallel: current bifurcates.
The method of converting non-standard circuit diagram into standard circuit diagram: current flow path method is adopted.
XI。 existing legislation
1. Electricity Q: The amount of charge is called electricity, and the unit is coulomb.
Current I: 1 sec, and the amount of electricity passing through the conductor section is called current intensity. Q=It
Unit of current: ampere (A) 1 ampere = 1000 mA The direction of positive charge directional motion is defined as the current direction.
Use ammeter to measure current, which is connected in series in the circuit, and the range is appropriate. It is not allowed to connect the ammeter directly to both ends of the power supply.
2. Voltage U: The cause of the current caused by the directional movement of free charge in the circuit. Voltage unit: Volt (V).
Use a voltmeter (voltmeter) to measure the voltage, which is connected in parallel at both ends of the circuit (electrical appliances and power supply) with appropriate range.
13. resistance r: the blocking effect of conductive objects on current. Symbol: r, unit: ohm, kiloohm, megaohm.
The resistance is directly proportional to the length of the wire, inversely proportional to the cross-sectional area product, and also related to the material.
Conductors with different resistances are connected in series in the circuit with the same current (1:1). Conductors with different resistances have the same voltage when connected in parallel in the circuit (1: 1).
3. ohm's law: formula: I = u/r u = IR r = u/i.
The current intensity in a conductor is proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.
Conductor resistance r = u/i. For a conductor, if the voltage changes, the current changes, but the resistance value remains the same.
5. Series circuit characteristics:
①I = I 1 = I2②U = U 1+U2③R = R 1+R2④U 1/R 1 = U2/R2
After two conductors with different resistances are connected in series, the voltage at both ends of the conductor with larger resistance is higher, and the conductor with smaller voltage at both ends has lower resistance.
For example, the lamp marked "6V, 3W" is connected to the circuit marked 8V. How to connect a resistor to make a small light bulb glow normally?
Solution: Since P = 3 watts, U = 6 volts.
∴ I = P/U = 3W/6V = 0.5A
Because the total voltage of 8 volts is greater than the rated voltage of 6 volts, an R2 should be connected in series, as shown in the right figure.
So U2 = U-U 1 = 8 volts -6 volts = 2 volts.
∴ R2 = U2/I = 2 volts /0.5 ampere = 4 ohms. Answer: (omitted)
6. The characteristics of parallel circuit:
① u = u1= u22i = I1+i231/r =1/r1+/R2 or 4i1r/kloc-.
Two conductors with different resistances are connected in parallel: the conductor with large resistance has small current and the conductor with large current has small resistance.
For example, as shown in Figure R2 = 6 ohms, the indicator of ammeter is 0.4 A when K is off, and the indicator of A is 1.2 A when K is off. Find: ①R 1 resistance ② power supply voltage ③ total resistance.
Known: I = 1.2 A I 1 = 0.4 A R2=6 Ohms.
Q: r1; u； rare
Solution: ∵R 1, R2 in parallel.
∴I2 = I-I 1 = 1.2a-0.4a = 0.8a
According to ohm's law, U2=I2R2=0.8 A× 6 ohms =4.8 volts.
∵R 1, R2 in parallel ∴ u = u1= U2 = 4.8V.
∴ r1= u1/I1= 4.8V/0.4Amp = 12 Ohm.
∴ R = U/I = 4.8V/ 1.2A = 4Ohm (or calculate the total resistance by formula) A: (omitted)
Twelve. electric energy
1. Electric work W: The work done by current is called electric work. The process of electric current doing work is the process of converting electric energy into other forms of energy.
Formula: w = uqw = UIT = U2t/r = I2RTW = Pt Unit: W Joule, U Volt, I Ampere, T Seconds, Q Library, P Watt.
3. Electric power P: the electric work done by the current in unit time, indicating the speed at which the current does work. Electrical appliances with large electric power can do work quickly with current.
Formula: P = W/T P = UI (P = U2/R P = I2r) Unit: W Joule, U Volt, I Ampere, T Seconds, Q Library, P Watt.
13. electric energy meter (watt-hour meter): an instrument for measuring the power consumption of electrical appliances. 1 kwh = 1 kwh = 1000 watts× 3600 seconds =3.6× 106 joules.
Example: How many hours can two "220V, 40W" lamps use 1 kWh?
Solution T = W/P = 1 kWh /(2×40 watts) = 1000 watts /80 watts = 12.5 hours.
Thirteen. attraction
1. Magnets repel magnetic poles with the same name and attract magnetic poles with different names.
The property that an object can attract substances such as iron, cobalt and nickel is called magnetism. A substance with magnetism is called a magnet. The poles of magnets always appear in pairs.
2. Magnetic field: There is an area around the magnet that acts on other magnets.
The basic property of magnetic field is to generate magnetic force to the magnet put in it.
Magnetic field direction: When the small magnetic needle is at rest, the direction pointed by the N pole is the magnetic field direction of this point. The magnetic field around the magnet is represented by magnetic induction lines.
The geomagnetic north pole is near the geographical south pole, and the geomagnetic south pole is near the geographical north pole.
3. Magnetic field of current: Oster experiment shows that there is a magnetic field around the current.
The energized solenoid is equivalent to a bar magnet.
The relationship between the direction of current in the energized solenoid and the polarity at both ends of the solenoid can be judged by the right-hand spiral rule.
Reference: To judge the motion of an object, another object must be selected as the standard, and the object selected as the standard is called the reference.
3. Uniform linear motion:
① Two methods to compare the speed of movement: A Compare the distance traveled in the same time. Compare the time required to drive the same distance.
② formula:1m/s = 3.6km/h.
Third, force.
Force F: Force is the action of an object on an object. The forces between objects always interact.
Unit of force: Newton (n). Instruments for measuring force: dynamometer; Spring scales are used in laboratories.
The function of force: to deform an object or change its motion state.
The change of the motion state of an object refers to the change of the speed or direction of the object.
The three elements of force: the size, direction and action point of force are called the three elements of force.
The diagram of force should be proportional; Schematic diagram of forces, not to scale.
3. Gravity G: the force exerted on an object due to the attraction of the earth. Direction: vertical downward.
The relationship between gravity and mass: g = mg m = g/g.
G=9.8 N/kg. Reading: 9.8 N/kg, that is to say, the weight of an object with a mass of 1 kg is 9.8 N. ..
Center of gravity: the point of action of gravity is called the center of gravity of an object. The center of gravity of a regular object is in the geometric center of the object.
2. Two-force balance condition: acting on the same object; These two forces are equal in magnitude and opposite in direction; Linear motion.
Under the balance of two forces, an object can be at rest or move in a straight line at a uniform speed.
The equilibrium state of an object means that the object is in a state of static or uniform linear motion. The resultant force of external forces on an object in equilibrium is zero.
5. Synthesis of two forces on the same line: same direction: resultant force f = f1+F2; The direction of resultant force is the same as that of F 1 and F2;
Opposite directions: the resultant force F=F 1-F2, and the resultant force direction is the same as the strong force direction.
Under the same conditions, rolling friction is much smaller than sliding friction.
Sliding friction is related to positive pressure, material characteristics and contact surface roughness. Sliding friction, rolling friction and static friction.
7. Newton's first law, also known as the law of inertia, means that all objects are always in a state of static or uniform linear motion when they are not affected by external forces. Inertia: The property that an object maintains its original static or uniform linear motion is called inertia.
Fourth, density.
⒈ Density ρ: the mass per unit volume of a substance, and density is a characteristic of the substance.
Formula: m=ρV International unit: kg/m3, common unit: g/cm3,
Relationship:1g/cm3 =1x103kg/m3; ρ water =/kloc-0 /×103kg/m3;
Reading: per cubic meter 103kg, which means that the mass of 1 cubic meter of water is 103kg.
1. Density measurement: measure the mass with a pallet balance, and measure the volume of solid or liquid with a measuring cylinder.
Area unit conversion:
1 cm2 = 1× 10-4 m2，
1 mm2 = 1× 10-6mm 2。
Verb (short for verb) pressure
1. pressure p: the pressure per unit area of an object is called pressure.
Pressure f: the force acting vertically on the surface of an object, in N. ..
The function of pressure is expressed by pressure, which is related to pressure and stress area.
Pressure unit: n/m2; Technical name: Pascal (Pa)
Formula: F=PS S: stress area, the common part of two objects in contact; Unit: square meters.
Methods of changing pressure: ① reducing pressure or increasing stress area can reduce pressure; ② Increasing the pressure or decreasing the stress area can increase the pressure.
1. liquid internal pressure: measure the liquid internal pressure: use a liquid manometer (u-tube manometer).
Reason: Because the liquid has gravity, it exerts pressure on the bottom of the container; Due to the fluidity of the liquid, pressure is generated on the wall of the device.
Law: ① At the same depth, the pressure in all directions is equal; ② The greater the depth, the greater the pressure; ③ Different liquids at the same depth, the higher the liquid density, the greater the pressure. [Depth h, the vertical height from the liquid surface to a certain point of the liquid. ]
Formula: p = P=ρgh h: unit: meter; ρ: kg/m3; G=9.8 N/kg.
13. Atmospheric pressure: gravity produces atmospheric pressure, which proves the existence of atmospheric pressure and is very large. It was the Madeborg Hemisphere Experiment and Torricelli (an Italian scientist) who measured the atmospheric pressure. After the Torricelli tube is tilted, the height of the mercury column remains unchanged and the length becomes longer.
1 standard atmospheric pressure = 76 cm mercury column height =1.01×105pa =10.336m water column height.
Instruments for measuring atmospheric pressure: barometer (mercury barometer, box barometer).
The law of atmospheric pressure changing with altitude: the higher the altitude, the smaller the pressure, that is, the lower the boiling point with the elevation.
Six, buoyancy
1. Buoyancy and its causes: An object immersed in liquid (or gas) is called buoyancy when it is pushed upward by liquid (or gas). Direction: vertically upward; Cause: the pressure difference between liquid and object.
2. Archimedes principle: An object immersed in a liquid is subjected to upward buoyancy, and the buoyancy is equal to the gravity when the object displaces the liquid.
That is, f float = G liquid discharge = ρ liquid gV discharge. (Line V represents the volume of liquid discharged by the object)
3. Buoyancy calculation formula: F float = G-T = ρ gV drainage = F up-down pressure difference.
4. When the object floats: F float = G object and ρ object.
When the object floats: f floats >; G and ρ < ρ liquid when the object sinks: ρ liquid when F floats.
Seven, simple machinery
1. Lever balance condition: f 1L 1 = f2l2. Force arm: the vertical distance from the fulcrum to the line of force action.
The purpose of keeping the lever in the water position by adjusting the nuts at both ends of the lever is to facilitate the direct measurement of the length of the power arm and the resistance arm.
Crown block: equivalent to an arm. It can't save energy, but it can change the direction of force.
Moving pulley: it is equivalent to a lever with twice the power arm as the resistance arm, which can save half of the force, but cannot change the direction of the force.
Work: two necessary factors: ① the force acting on the object; ② The passing distance of the object in the direction of force. W = W unit =FS Work: Joule.
3. Power: the work done by an object in unit time. A physical quantity indicating the speed at which an object does work, that is, an object with high power does work quickly.
W = unit W = Pt P:watt；; Unit of w: joule; Unit of t: seconds.
Eight, light
1. Linear propagation of light: Light propagates linearly in the same homogeneous medium. Aperture imaging, shadow and spot are all linear propagation phenomena of light.
The maximum speed of light in vacuum is 3x108m/s = 3x105km/s.
Law of light reflection: one side, two sides and three dimensions. The angle between the incident light and the normal is the incident angle. The angle between the reflected light and the normal is the reflection angle.
Imaging characteristics of plane mirror: virtual image, equal size, equal distance and mirror symmetry. The reflection of objects in water is the reflection of virtual images and light.
3. The phenomenon and law of light refraction: Seeing the virtual image of chopsticks and fish in water is the phenomenon of light refraction.
Convex lens has the function of converging light, while concave lens has the function of diverging light. The law of refraction of light: one side, two sides, three sides, big four empty.
3. The law of convex lens imaging: [When u = f, no imaging; When U=2f, V=2f becomes a real image with inverted size]
Properties of object distance U image distance V image Application of light path diagram
U & gt2f f<v & lt2f Inverted Micro Reality Camera
F<u & lt2f v & gt2f Inverted Amplification Real Slide Projector
U< magnifying glass
⒌ Convex lens imaging experiment: Put the candle, convex lens and light screen on the optical bench in turn, so that the centers of the candle flame, convex lens and light screen are at the same height.
Nine, thermal energy:
1. temperature t: indicates the degree of heat and cold of the object. It is a state quantity.
Principle of common thermometer: According to the characteristics of liquid expanding when heated and contracting when cooled.
The differences between thermometers and thermometers are: ① range, ② minimum scale, ③ glass bulb, curved thin tube and ④ usage.
2. Heat transfer conditions: temperature difference. Heat: the heat absorbed or released by an object during heat transfer. This is a process quantity.
There are three ways of heat transfer: conduction (heat is transferred along an object), convection (heat is realized by the flow of liquid or gas) and radiation (heat is directly emitted from a high-temperature object).
3. Vaporization: the phenomenon that a substance changes from a liquid state to a gas state. Mode: evaporation and boiling, evaporation should absorb heat.
The factors that affect the evaporation rate are: ① liquid temperature, ② liquid surface area and ③ air flow on the liquid surface. Evaporation has a cooling effect.
1. specific heat capacity c: the heat absorbed by a substance with unit mass when the temperature rises by 65438 0℃ is called the specific heat capacity of the substance.
Specific heat capacity is one of the characteristics of matter, and the unit is coke/(kg℃). The specific heat capacity of water in common substances is the largest.
C water = 4.2× 103 joules/(kg℃), reading: 4.2× 103 joules per kg℃.
Physical meaning: The mass of water is 1 kg, the temperature of water rises 1℃, and the absorbed heat is 4.2× 103 Joule.
⒌ Thermal calculation: Q discharge = cm ⊿ t q decrease and intake = cm ⊿ t liter.
Q is directly proportional to c, m and ⊿t, and inversely proportional to c, m and ⊿ t ⊿ t = q/cm.
6. Internal energy: the sum of kinetic energy and molecular potential energy of all molecules in an object. All objects have internal energy. Internal energy unit: Joule
The internal energy of an object is related to its temperature. When the temperature of an object increases, the internal energy increases; When the temperature decreases, the internal energy decreases.
Methods of changing the internal energy of an object: work and heat transfer (equivalent to changing the internal energy of an object)
7. Law of energy transformation and conservation: energy will neither be generated out of thin air nor disappear out of thin air, but will only be transformed from one form to another, or transferred from one object to another, and the total amount of energy will remain unchanged.
Circuit
The circuit consists of power supply, electric key, electrical appliances, wires and other components. In order to have a continuous current in the circuit, there must be a power supply in the circuit and the circuit should be closed. The circuit has the phenomena of access, open circuit (open circuit), short circuit of power supply and electrical appliances.
2. A substance that conducts electricity easily is called a conductor. Such as aqueous solutions of metals, acids, bases and salts. Substances that do not conduct electricity easily are called insulators. Such as wood and glass.
Under certain conditions, an insulator can become a conductor.
3. Identification of series-parallel circuits: series: current does not bifurcate, parallel: current bifurcates.
The method of converting non-standard circuit diagram into standard circuit diagram: current flow path method is adopted.
XI。 existing legislation
1. Electricity Q: The amount of charge is called electricity, and the unit is coulomb.
Current I: 1 sec, and the amount of electricity passing through the conductor section is called current intensity. Q=It
Unit of current: ampere (A) 1 ampere = 1000 mA The direction of positive charge directional motion is defined as the current direction.
Use ammeter to measure current, which is connected in series in the circuit, and the range is appropriate. It is not allowed to connect the ammeter directly to both ends of the power supply.
2. Voltage U: The cause of the current caused by the directional movement of free charge in the circuit. Voltage unit: Volt (V).
Use a voltmeter (voltmeter) to measure the voltage, which is connected in parallel at both ends of the circuit (electrical appliances and power supply) with appropriate range.
13. resistance r: the blocking effect of conductive objects on current. Symbol: r, unit: ohm, kiloohm, megaohm.
The resistance is directly proportional to the length of the wire, inversely proportional to the cross-sectional area product, and also related to the material.
Conductors with different resistances are connected in series in the circuit with the same current (1:1). Conductors with different resistances have the same voltage when connected in parallel in the circuit (1: 1).
3. ohm's law: formula: I = u/r u = IR r = u/i.
The current intensity in a conductor is proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.
Conductor resistance r = u/i. For a conductor, if the voltage changes, the current changes, but the resistance value remains the same.
5. Series circuit characteristics:
①I = I 1 = I2②U = U 1+U2③R = R 1+R2④U 1/R 1 = U2/R2
After two conductors with different resistances are connected in series, the voltage at both ends of the conductor with larger resistance is higher, and the conductor with smaller voltage at both ends has lower resistance.
For example, the lamp marked "6V, 3W" is connected to the circuit marked 8V. How to connect a resistor to make a small light bulb glow normally?
Solution: Since P = 3 watts, U = 6 volts.
∴ I = P/U = 3W/6V = 0.5A
Because the total voltage of 8 volts is greater than the rated voltage of 6 volts, an R2 should be connected in series, as shown in the right figure.
So U2 = U-U 1 = 8 volts -6 volts = 2 volts.
∴ R2 = U2/I = 2 volts /0.5 ampere = 4 ohms. Answer: (omitted)
6. The characteristics of parallel circuit:
① u = u1= u22i = I1+i231/r =1/r1+/R2 or 4i1r/kloc-.
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