What are the answers to the exercises after class in Physics 3-2 textbook of senior high school?

Guangdong Education Edition Physics Elective Course 1- 1 Textbook Answer

chapter one

The first part.

[Observation and Thinking] (1) An empty aluminum can will roll from a static state to a balloon.

(2) ① When the metal ball is in contact with the electroscope, the two metal foils are opened. (2) When the above experimental process is repeated for many times, the opening angle of the two metal foils becomes larger.

(3) When the metal ball C approaches the conductors A and B which are in contact with each other, two pairs of metal foils are opened; After the conductors A and B are separated, then the metal ball C is removed, and two pairs of metal foils are opened; After contacting A and B again, two pairs of metal foils are closed.

[Discussion and communication] 1. Clothes rub against each other during drying, which makes clothes and socks have different charges. According to the characteristics of different charge attraction, socks "stick" to clothes.

2. Microscopic explanation: triboelectrification is essentially caused by electron transfer between objects. It is impossible to generate charges out of thin air, so the statement of "triboelectricity" is wrong.

Exercise after class: 1. American Broadcasting Company Inc (ABC)

2.( 1) Contact for charging. (2) Let two uncharged conductors contact each other, and move the charged conductor closer to induce positive and negative charges respectively. Then separate the conductors with positive and negative charges, and touch the conductors with positive charges with your hands to guide the positive charges away; Finally, the uncharged conductor contacts the negatively charged conductor, so that they are all negatively charged. (3) Two uncharged conductors touch each other, and the charged conductor approaches them, and then they separate.

3. The charged electroscope will bring different charges to the near end of the uncharged conductor. Different charges attract each other, which makes the charge on the gold foil move upward continuously, and the charge on the gold foil becomes smaller and smaller, so the opening angle decreases.

Section 2.

[Discussion communication] (1) Like charges repel each other, but different charges attract each other; Magnetic poles of the same name repel each other, but magnetic poles of different names attract each other. (2) Hair has the same charge and repels each other.

[Observation and Thinking] Observed phenomenon: When the charges of the two balls remain unchanged, the deflection angle of the foam ball increases with the decrease of the distance between the two balls; When the charge of the metal ball decreases, the deflection angle of the foam ball decreases when the distance between the two balls remains unchanged.

2. The amount of charge carried by the big ball can be changed by using the induction starter, and there is interaction between the charges.

Step 3: No.

Exercise 1. ABD 2。 ABC after class

3. It should be placed between AB lines. Let the distance between point charge c and point charge a be x meters, according to Coulomb's law.

KqAqC/x=kqBqC/(0. 15-x) so x = 0.05m

This position has nothing to do with the number and sign of point charge C.

Section 3.

Exercise after class 1. The magnetic field at point A is stronger than that at point B, and the direction is different. 2. The small magnetic needle will rotate clockwise, and the N pole will eventually point to the direction of B. ..

3.= BS = 2.0× 10-2×5.0× 10-2 = 1.0× 10-3Wb

Section 4.

[Discussion and communication]

Description of field electric field intensity and magnetic induction intensity

The intensity of the directional electric field is a vector.

The direction of positive charge at a point in an electric field passes through the point.

The tangent direction of the electric field line is also the square of the electric field intensity at this point.

Electric field lines start with positive charge or infinity and end with negative charge or infinity.

Infinite. It's not closed. The magnetic induction intensity is a vector.

A point in a magnetic field through which the north pole of a small magnetic needle passes.

The tangential direction of the magnetic induction line is also the magnetic induction intensity at this point.

Direction.

The magnetic induction line is a closed curve, and the magnetic induction line outside the magnet is northward.

The magnetic pole extends back to the south pole of the magnet, from the south pole to the inside.

Arctic.

The density of large and small electric field lines indicates the strength of electric field, and the density of magnetic induction lines indicates the strength of magnetic induction.

1. cannot intersect. If the electric field lines intersect, two different electric field directions will appear at the intersection.

This statement is incorrect. Only when the electric field line is a straight line, and the initial velocity of charged particles is zero or the initial velocity direction is on this straight line, the motion trajectory coincides with the electric field line.

Section 5.

[Experimental Exploration] Observation phenomenon: After the circuit is connected, the compass direction changes. Conclusion: Current produces magnetic field.

[Discussion and Communication] The current magnetic effect discovered by Oster confirmed the connection between electricity and magnetism, broke through the long-standing rigid concept that electricity has nothing to do with magnetism, laid the foundation for the development of electromagnetic theory, and initiated a new era of electromagnetic research.

[Observation and Thinking] 1. Entrance 2. Size 3. Experimental conclusion: A charged wire placed vertically in a magnetic field will be subjected to a force (Ampere force). If the direction of current changes, the direction of force will also change; When the current changes, so does the force.

1. According to the right-hand rule.

B.C.

2. The electrified wire is not affected by ampere force.

3. Current balance principle and ammeter.

Section 6.

[Observation and Thinking] Experimental phenomenon: When the magnetic field is not applied, the trajectory of the electron beam is straight when the cathode ray tube works; When the vertical magnetic field is applied, the trajectory of the electron beam is curved when the cathode ray tube works, and the Lorentz force direction is perpendicular to the magnetic field direction.

The linear force (a) decreases from outside to inside, and (b) increases from inside to outside.

Exercise after class 1. Not correct. 2. Lorentz force exerts a magnetic field

The exercises in this chapter

1. The rubbed balloon and TV screen are charged, so it can attract the hair on the arm.

You can collect information by surfing the Internet and consulting related books.

3. First, determine which physical quantities to study. This experiment can study the relationship among current, number of turns and number of nails. The control variable method is: first, keep one physical quantity unchanged and study the relationship between the other two physical quantities; Then keep another physical quantity unchanged, and then study the relationship between the other two physical quantities.

5. If the electron beam does not deflect, there may be a magnetic field, but the direction of the magnetic field and the direction of the electron beam movement are in a straight line. If the electron beam is deflected, there may be a magnetic field or an electric field force to deflect the electron.

6. There is a magnetic field around the oven and refrigerator. The object next to it will be magnetized and become a magnet, which can deflect the compass.

8. It is related to the current and the distance to the conductor. Place another conductor with constant current nearby and observe its bending, so as to know its stress and analyze the magnetic field strength.

9. According to the judgment method of Lorentz force, we can know that plate A is negatively charged and plate B is positively charged. The two plates A and B continuously accumulate charges to form a voltage, and the current passes through the resistor from bottom to top.

chapter two

The first part.

2. There will be no induced current, because the magnetic flux passing through the plane of the lead frame will not change during the movement from left to right in the paper.

Section 3.

1. When the gear teeth leave or approach the dotted line due to rotation, the distance between the gear teeth and the magnet changes. When the gear teeth are magnetized by the magnet, the magnetic flux passing through the coil changes, so the induced current is generated in the coil.

2.50 50 50 60 50 50

3. The higher the frequency of alternating current, the faster the magnetic flux produced by alternating current in metal workpiece changes. According to Faraday's law of electromagnetic induction, the greater the induced electromotive force generated by electromagnetic induction in the metal workpiece, the greater the induced current output, so the greater the heat generated at the weld.

4. Because the input power of the primary coil is equal to the output power of the secondary coil, the input power of the primary coil is equal to the output power of the secondary coil.

Pl=P2

And Pl=U 1I 1.

P2=U2 I2

So U 1/ U2= I2/ I 1.

The relationship between the number of turns of primary and secondary windings of transformer and voltage is as follows

U 1/ U2= n 1/ n2

I 1/I2=n2/n 1 can be obtained from the above two formulas.

Section 4.

1. Advertisement

2. Mobile communication, radio broadcasting, television, wireless remote control, radar speed measurement, etc.

The exercises in this chapter

1.BD Tip: Only the changing electric field can excite the magnetic field, and the changing magnetic field can excite the electric field, so A is wrong; Light travels at different speeds in different media, so C is wrong.

2.D

4. At present, the common power generation methods are: thermal power generation, hydroelectric power generation, nuclear power generation, wind power generation, solar power generation, tidal power generation, geothermal power generation and so on. At present, the main power generation modes in China are: thermal power generation, hydropower generation and nuclear power generation.

Telephone, microwave oven, induction cooker and tape recorder are used in household appliances.

6 Solution: (1) When the user works normally, there is no voltage between A and B. Since one side of the primary coil adopts the double-wire winding method of live wire and neutral wire, when the user works normally, the current flowing through live wire and neutral wire at any time is equal in magnitude and opposite in direction, so the magnetic flux flowing through transformer core J is zero, so there is no voltage between A and B. 。

(2) If someone is standing on the ground in the room and his hand accidentally touches a live wire to get an electric shock, the trip switch will be turned off. Because the currents flowing through the live wire and the neutral wire are no longer equal, the magnetic flux in the iron core P changes at this time, and a voltage appears between A and B, which causes the controller Q to act and the trip switch to disengage.

7.BCD

8 solution: let the number of turns of the primary coil be n,

Only when s 1 is closed, n/n 1 = u/u 1, n/n1= i1/i.

When s2 is only closed, n/N2 = u/U2 and n/N2 = I2/I.

Because r 1 = R2, n/N2 = u/U2, i 1 = u 1/r 1, I2 = U2/R2.

It can be solved by the above formula: n 1:n2= 1:

Chapter three.

The first part.

[Discussion and Communication] Telephone: It enables people in different places to break through the limitation of space and make real-time contact, fundamentally changing the way of human communication, making the earth smaller, speeding up the pace of work, profoundly affecting people's lifestyles and interpersonal relationships, and forming a huge communication industry.

Television: it can spread moving images to very distant places at the speed of light, completely changing the way of information dissemination of human beings, and soon becoming the main medium of information dissemination, having a far-reaching impact on people's lifestyle and even becoming an important factor in social change.

Engine: Henry 1929

Generator: Siemens 1866 can realize the conversion with other energy forms, provide efficient, clean and cheap electric energy for human beings, promote the large-scale application of electric energy, expand the range of human energy utilization and promote the transformation of energy utilization mode.

Electric light: Edison dispelled the darkness and greatly expanded the space and time for human activities.

Alternating current power transmission and transformation technology: Tesla 19 In the late 1980s, people were able to effectively transmit the power generated by power stations to distant places without the limitation of spatial distance.

Section 2.

[Discussion and communication] The utilization of coal is a great pioneering work for human beings to develop energy. It supported the first industrial revolution driven by the steam engine. Britain has become a world industrial power by virtue of its advantages in coal utilization technology. Later, with the popularization of oil, oil became the "blood" of industry, which greatly accelerated the process of world industrialization. The United States surpassed Britain because of its development and innovation in oil utilization technology. It has become the world's largest industrial power. Another example is the invention and improvement of the steam engine, which changed the way people use energy for the first time, provided great impetus for industrial development, triggered the first industrial revolution in history, and established a large industrial system based on machines. Many countries have quickly completed the process of Tm industrialization and entered the era of industrial civilization.

[Discussion and Communication] People usually convert the internal energy, geothermal energy and solar energy generated by conventional fuel combustion or nuclear reaction into mechanical energy, which is called heat engine? Heat engines rely on working substances (such as water vapor, air or combustion gas) to complete the conversion of heat into work. Steam engines, gas turbines, internal combustion engines and jet propulsion engines are all heat engines. Both heat engines and motors can convert other forms of energy into mechanical energy? The main difference between the two is that the motor realizes mechanical movement through the connection of electricity and magnetism, while the heat engine completes the conversion of heat and work with the help of working fluid. The efficiency of modern motors has reached more than 98%. Compared with electric motors, heat engines have low efficiency (less than 40%) and seriously pollute the environment.

Exercise after class 1. ① Disadvantages of heat engine: low efficiency, serious pollution, loud noise, inconvenient use, etc. (2) generators can convert other forms of energy into electric energy, and motors can easily convert electric energy into other forms of energy, so all kinds of energy can be converted through electric energy. ⑧ Electric energy has the advantages of cleanness, high efficiency, easy conversion, easy transmission and easy control.

2.

The cost of coal is moderate, it is easy to build a thermal power station, and its reserves are abundant. Large mining areas are concentrated. Mining destroys land and water resources, which is harmful to mines.

Workers are highly dangerous. Burning coal and coal will cause serious air pollution.

A lot of cinders.

Oil costs are moderate, reserves are abundant, large mining areas are concentrated, oil prices are changeable, and oil leakage will seriously pollute the soil.

Soil and water also produce air pollution when burning oil.

Natural gas has moderate cost, abundant reserves and large mining areas.

Hydropower operation cost is low, there is no waste, and the investment in pollution-free power station construction is large. The reservoir flooded a large area of land and disturbed the river.

Animal life.

Nuclear energy has low operating cost and generally does not produce air pollution. The investment in building a station is large, and waste disposal is a difficult problem, and nuclear leakage occurs from time to time.

The danger of dew.

Section 3.

[Discussion and communication] The rice cooker uses a temperature sensor to detect the temperature, the automatic door uses an infrared sensor and a pressure sensor, the infrared sensor is used to detect whether there are people and animals at the door, the pressure sensor is used to detect whether there are objects between the two doors when the door is closed, and the camera senses the brightness and color of light through a light sensor.

Section 5.

Practice and development: sulfur dioxide 5.8×108×1672×1.05% =1.02×10/0 kg ash 5.8×/kloc-. Dust 5.8×108×1000× 26 %× (1-97.5%) = 3.77×109.

Exercise after class 1. Disadvantages of hydropower stations: flooding a large number of cultivated land requires a large number of immigrants. Large reservoirs flooded some animal and plant habitats and many cultural relics. The dam of hydropower station cuts off the migration channel of migratory fish and destroys the natural ecology. Large reservoirs may also induce earthquakes and other environmental geological problems.

Disadvantages of thermal power plants: the mining industry destroys land and water resources, which is very dangerous to miners. When burning coal, it produces serious air pollution and a lot of cinders.

The exercises in this chapter

4. The positive effects have become a household name, and the negative effects are gradually exposed. People communicate more and more frequently and conveniently. The internet has enabled mankind to enter the information society, and it has become easier and easier to obtain, process, store and disseminate information, which has improved the level of social productivity and changed people's production, life and even way of thinking? However, with the increasing integration and assimilation of completely different cultures, the "cultural ecology" is facing imbalance and the "cultural diversity" is challenged. In addition, developed countries are exporting their culture, ideas and values to all parts of the world with the slogan of "global economic integration", which further affects the changes of world political and economic structure.

chapter four

The first part.

[Discussion and communication] The second question is that the intelligent control of air conditioners can use sensors such as infrared, light and temperature. To make the air conditioner truly "feel" people's feelings, a temperature sensor can be set near people, such as a remote controller, so that the temperature around the human body can be accurately measured and fed back to the air conditioner. Here, we can review the sensors introduced in the previous chapter.

2. Hint and answer: In general, the brightness of the electric lamp is constant. When reading a book, people require a certain illumination brightness, but the brightness of the surrounding environment changes. A "smart lamp" can adjust its brightness according to the brightness change of the surrounding environment, so as to keep the illumination brightness of books unchanged. Therefore, we can consider installing a light sensor on the lamp holder to convert light information into electrical information, so as to automatically control the brightness of the lamp.

Section 2.

[Discussion and communication] The microwave oven directly acts on food molecules with the help of microwaves, and the food is heated together inside and outside; The induction cooker uses electromagnetic induction to heat the pot, and heats the food through heat transfer, and the temperature rises from outside to inside.

1. Microwave oven: glass, ceramics.

Induction cooker: iron, stainless steel

Rice cookers: aluminum, copper, iron, stainless steel, silver

Metal cookers that reflect microwaves cannot be used in microwave ovens. Generally, non-ferromagnetic materials should not be used as cooking utensils for induction cookers unless high-frequency AC power is used (for example, aluminum pot can be used for induction cookers with AC frequency of 60 kHz). Cooking utensils in rice cookers are usually made of metal materials with strong thermal conductivity.

2. There is a strong magnet on the speaker, which will affect the distribution of magnetic powder on the disk and make the recorded information lost.

3. The safety part and the working part of household appliances should be connected in series in the circuit towel, and the current of the working part should be cut off by the action of the safety part to eliminate the hidden danger of accidents.

Section 3.

[Discussion and communication] Find the difference between the two refrigerators in function, volume and price, and judge the applicable place accordingly; Both can be used in family and hotel rooms, or in kitchens and bedrooms. There is no conclusion, as long as there is a reasonable basis.

[Discussion and communication] The choice is well-founded. Here, we should emphasize the integration of various factors and make a final judgment according to the actual situation. If all three TV sets in the statement list are not suitable for our home, are they allowed to choose reasonably?

Exercise after class 1. For example, the main technical parameters of electric fans are rated voltage, frequency, total input power, air volume, speed and so on.

2.I= = =0.25 A

3. electricity consumption for one month: W=Pt= ×30=39 kW? h

Electricity payable: m = 39× 0.85 = 33. 15 (yuan)

Section 4.

Observation: With the change of the slider position, the brightness of the light bulb also changes.

Conclusion: The resistance in the circuit increases and the current decreases. When the resistance becomes smaller, the current increases.

Observed phenomena: when the DC power supply is connected, the light bulb does not light up; When connected to an AC power supply, the light bulb will emit light.

Conclusion: AC power supply passes through capacitor; Does the capacitor block direct current?

Observed phenomena: when the DC power supply is connected, the light bulb lights up; When the AC power supply is connected, the bulb hardly emits light, except for a dim bright spot at the filament.

Conclusion: DC can pass through the sensor. Inductors are obstacles to alternating current.

After-class exercise 1.a is a bass speaker and b is a tweeter.

2. When the switch is connected to the AC power supply (terminal A), D 1 is turned on, and there is only a dim bright spot at the D2 filament. When the switch is connected to the DC power supply (terminal B), D 1 is turned off and D2 is turned on.

Section 5.

[Discussion and communication] (1) Students are free to discuss. Other factors to be considered are: reasonable selection of fuse specifications, not copper wires; Switch sockets should be moisture-proof, and so on. (2) People standing on the ground have voltage between them and live wires. When leakage occurs, the electric drill shell of the three-pin plug has been grounded, and the human body is equivalent to being connected in parallel with the electric drill. The resistance of grounding from the live wire through the ground wire is much larger than the resistance dust of grounding through the human body, and the current basically flows through the ground wire to ensure human safety. However, the electric drill with two-pin plug will flow through the human body when it leaks electricity, endangering life safety.

Exercise after class 1. (a) There is a switch on the socket. After plugging in, the user can turn off the switch and let the appliance work. This can prevent the plug from being plugged into the socket when the power is on, and the ignition is caused by poor contact. (2) This socket is equipped with a protective door, which can not only prevent dust, but also prevent children from playing in the socket with metal pieces. Cause a safety accident. (c) It is a three-pin socket, a two-pin socket, a round-pin socket and a "flat-pin socket". This versatility makes the round pin plug easy to insert in the wrong direction, causing safety accidents, and it is best not to use it. (d) It is a three-pin socket with a waterproof cover, which is suitable for places such as toilets.

This mobile socket can't be used because the refrigerator needs grounding. The original plug is three-legged, while the mobile socket has only two wires, namely zero wire and live wire. The ground wire of the refrigerator is actually suspended, which can't play the role of grounding.

3. The leakage current should be controlled to the extent that it is harmful to people, but it should not be too small. Otherwise, in wet weather, the slight leakage of the circuit will make the leakage protection switch work and affect the normal power consumption. You can choose between 0.01~ 0.05a.

The exercises in this chapter

1. Assuming that all electrical appliances work at the same time, the current in the circuit at this time is

I =1.1.6+1.9+3.6+0.45× 6+5 =14.9a You can choose 15(30)A watt-hour meter.

2. It can be considered from the working principle of household appliances. For example, cathode ray tube displays include televisions, computer monitors, and the like. The deflected electron beam hits the phosphor screen to realize imaging, and the magnetic field will affect the deflection of the electron beam. Another example is that magnetic recording media include audio tapes, video tapes, computer disks, etc. , recording information with magnetic powder; However, the magnetic field will affect the distribution of magnetic powder and make the information lost. There are also objects made of ferromagnetic substances, such as mechanical watches, whose hairsprings are magnetized and cannot walk accurately.

4.( 1) Appropriate household appliances should be selected according to the family population and actual needs, and large-scale should not be pursued unilaterally; Reasonable arrangement of lighting equipment, using high light efficiency and energy-saving light sources, etc.

(2) Develop a good habit of using electricity, such as turning off the lights when people leave.