1. Only one of the four options given in the following multiple-choice questions is correct. Fill the letter before the correct option in the brackets after the question (3 points for each question, *** 15 points).
1. Xiao Liang bought an iron can with a glass bottle from the supermarket and tried to open the bottle cap, but he couldn't unscrew it. Liang Xiao's brother gently pried a few times along the edge of the bottle cap with a screwdriver and then unscrewed the bottle cap. This is mainly because the bottle cap can be pried open with a screwdriver.
A. increase the diameter of the bottle cap and reduce the pressure of the side wall of the bottle cap on the bottle.
B, reduce the contact area between the bottle cap and the bottle mouth.
C, reduce the pressure difference of gas inside and outside the bottle.
D because one side of the cover is pried open, the pressure on the other side of the cover increases.
2. There is a metal wire (or two wires) at the top of the iron tower of the high-voltage transmission line, which is thinner than the transmission line below (as shown in Figure 1 ~ Figure 2). Its function is []
A. strengthen the stability of the tower B. transmit the current of the neutral line.
C. lightning protection plays the role of lightning rod.
D as a backup line for emergency use when the transmission line is disconnected.
3. When taking pictures with a common camera, it is inconvenient to focus according to the distance between the subject and the camera lens. There is a kind of "fool" camera, as long as you include all the scenes you want to shoot in the viewfinder, the photos will be clearer regardless of the objects near and far, thus making the process of taking pictures very fast. The secret of this "fool" camera without "focus" is []
A. A lens with a long focal length is adopted, so that the imaging positions of different objects near and far are not much different.
B short focal length lens is used to make the imaging positions of different objects near and far have little difference.
C adopt a long focal length lens to make the imaging positions of objects at different distances the same.
D use a lens with short focal length to make the imaging position of different objects near and far the same.
The tape recorder can record and play, and its main components are running magnetic tape and magnetic head wound with coil. When recording, the magnetic powder on the magnetic tape is magnetized by the magnetic field generated by the current converted from the sound signal, so that the sound signal is converted into a magnetic signal and recorded on the magnetic tape; When playing, the magnetic signal on the tape is converted into an electrical signal by the magnetic head, which makes the speaker sound. For the basic principle of tape recorder recording and playback process, the following statement is correct []
A The basic principle of recording is electromagnetic induction, and the basic principle of playing is the magnetic effect of current.
B The basic principle of recording is the magnetic effect of current, and the basic principle of playing is electromagnetic induction.
The basic principle of C recording and playback is the magnetic effect of current.
D The basic principle of recording and playing is electromagnetic induction.
Wang Yong saw an automatic door in the hotel. The door will open and close automatically when someone comes near. Wang Yong is very interested in this. He wants to know how the automatic door is automatically controlled. To this end, he repeated several experiments: when he approached the automatic door gently, the door opened automatically; When a football rolls onto the automatic door, the door opens automatically; When a large colorless transparent glass plate with a ball at the bottom slides vertically towards the automatic door, the door will not open. According to the results of the inquiry test, Wang Yong put forward the following conjecture about the automatic control principle of the automatic door. What do you think is the most reasonable?
A. When the automatic door "listens" to the voice of the visitor, it can be automatically opened and closed through the voice control device.
B. The automatic door detects the infrared emitted by the approaching object, and the automatic switch is realized through the light control device.
C the automatic door itself can send out infrared signals, which will automatically open and close when it is reflected by an approaching object.
D, objects close to the door can generate pressure through air and transmit it to the automatic door to realize automatic opening and closing.
Ii. Fill in the blanks (* *15)
1.(3 points) As shown in Figure 3, Xiao Ting went to grandma's house for a holiday by car, and the car was driving on a straight expressway. Xiao Ting's feeling is that the distant village is moving in the opposite direction to the telephone pole; The nearby small trees are facing the telephone poles.
Exercise; The scenery around the telephone pole seems to be turning clockwise around it.
2.(3 points) The food sold on the train is often put on the trolley, as shown in Figure 4. If the goods are evenly placed on the car, when the front wheel meets the obstacle A, the salesman presses the handle down, then the car can be regarded as a lever, and the fulcrum is (write the letter of the fulcrum position); When the rear wheel meets the obstacle A, the salesman lifts the handle upward, and the fulcrum is. In the latter case, the trolley can be regarded as a force lever.
3.(3 points) In the plateau area above 3000m above sea level, the cooling water of automobile engines is easy to boil, which is because of the plateau area. When people who live in the plain all the year round arrive in the area, they will have an anoxic reaction because of the thin air. In order to get enough oxygen, people will unconsciously take a deep breath, and then the volume of the lungs will expand more than that in the plain (choose "big" or "small").
4.(3 points) The mechanical odometer on the car uses a set of counting gears installed on the wheels to realize counting, and these counting gears are driven by the rotation of the wheels through a specific transmission device. At the same time, the rotation of the wheel is transmitted to the sensor made of electromagnetic induction principle through a specific transmission device, and the sensor displays the electric signal reflecting the rotation of the wheel on the speedometer, thus indicating the speed at this time. When the tire has obvious wear after long-term use, it will cause errors in the calculated mileage and the indicated speed. If the mileage recorded in the odometer is 12000km, the actual mileage of the vehicle is (fill in "greater than", "less than" or "equal to"); If the car travels from Beijing to Shanghai, the estimated travel time of the whole trip will be (fill in "greater than", "less than" or "equal to") the actual time.
5.(3 points) At the Spring Festival party in 2005, a group of deaf-mute youths gave people beautiful enjoyment and good enlightenment with their exquisite dance Guanyin with a thousand hands.
(1) As shown in Figure 5, the audience can't see other dancers standing behind the lead dancer Tai Lihua, because the light is diffused.
(2) In the process of watching the performance, although we didn't see the band, we could tell which instrument was making sound, mainly because different instruments made different sounds.
(3) TV viewers see the thousand-handed Guanyin on the lotus seat wearing gorgeous glow, which is made up of three primary colors mixed in different proportions.
III. Briefly answer the following questions (***22 points)
1.(4 minutes) When the rocket is launched, if the high-temperature flame is sprayed down to the launch pad, the launch pad will be burned. In order to protect the launch pad, a large pool was built at its bottom, thus skillfully solving this technical problem.
(1) What is the huge white air mass ejected from the bottom when the rocket is launched (Figure 6)? How is it formed?
(2) Analyze the reason why the "big pool" plays a protective role on the launch pad.
2.(4 points) Some insulators as shown in Figure 7 are often seen in high-voltage transmission lines. Please explain why the surface of insulators hanging high voltage transmission lines should be painted with bright enamel and made into sections.
3.(4 points) Xiao Zhi bought a small colored lantern to decorate the festival. He found that when the filament of one small lamp burned out, the other small lamps could continue to shine. So Xiao Zhi became interested in the connection between small lanterns, so he consulted scientific and technical personnel and got the following information.
The size of the small lantern he used was "2.5 V, 0.25 A". By connecting a certain number of small lanterns in series, the voltage applied at both ends of a single small lantern is slightly lower than its rated voltage, and each small lantern can basically emit light normally.
The structure of small colored lights is shown in Figure 8. In addition to the fixed filament and small glass beads, about 4 turns of thin metal wire are wound on the filament conductive bracket. The filament resistance is about 2.5 Ω when it is cold and about 15 when it is hot.
The resistance of the thin metal wire is 1ω. Under normal (low voltage) conditions, because there is a layer of copper oxide on the surface of the support, it is not conductive to the filament support, and no current passes through it. If a higher voltage (such as 220 V) is applied, the oxide layer can be broken down, and the thin metal wire is connected with the filament holder.
According to the above information, please explain why the filament of the small lantern can continue to shine after burning.
4.(4 points) The broadcasting room of Xiangyang Middle School wants to control the speakers of the north and south teaching buildings with the help of the double-pole double-throw switch: when the switch is turned to the A end, the three speakers in the south are connected, and when the switch is turned to the B end, all the six speakers in the north and south are connected. According to the above requirements, please complete the circuit diagram in Figure 9 with a stroke line instead of a wire.
5.(6 points) For a long time, solid clay bricks have been the main building materials in China. Because there are many disadvantages in the production of clay brick, the relevant departments of the state put forward the requirements of reducing the utilization rate of clay brick and advocating new materials. The cement brick shown in figure 10 is a new building material. Please analyze the advantages of using hollow cement brick over solid clay brick from the aspects of energy saving and environmental protection. [Write at least three articles]
(6 points) Li Ming's family wants to buy a kettle to boil water. There are two kinds of aluminum pots with the same volume but different varieties to choose from in the supermarket. One is used on a liquefied gas stove, and the other is equipped with an electric heater, as shown in figure 1 1. Li Ming wants to compare which kettle is more economical to boil water He first conducted an investigation and got the following information: the electricity price of local residents is 0.5 yuan/kWh; The price of bottled liquefied gas is 60 yuan/bottle (the mass of each bottle of liquefied gas is about 15 kg, and the calorific value of liquefied gas is 4.2×107j/kg); The thermal efficiency of boiling water with liquefied gas is about 30%, and that of boiling water with electric kettle is about 90%. According to the above information, please calculate and analyze which kettle is more economical to use for boiling water.
Verb (abbreviation of verb) (8 points) In order to protect the environment and control soil erosion, the environmental protection team of the school designed and conducted a study on the river sediment concentration.
The first stage is theoretical analysis: ρ water, ρ sand and ρ muddy water represent the density of water, sediment and sediment water respectively, and X represents the quality of sediment contained in each cubic meter of sediment water (called sediment concentration), and the relationship between ρ muddy water and ρ water, ρ sand and X is deduced; Then, the image of the density ρ of sediment water, muddy water and water changing with sediment concentration X is made.
The second stage is experimental verification: put a certain amount of dry loess into the measuring cylinder, then pour a certain amount of clear water, calculate the sediment concentration X, and measure the density of sediment water ρ mud water; Then, clear water is added for many times to prepare sediment water with different densities, and the same calculation and measurement are carried out to obtain multiple groups of ρ mud water and X data; Then, according to these data, a ρ mud-X image is made to show the relationship between the density of sediment water and the concentration of sediment. They were surprised to find that the experimental results were consistent with the theoretical analysis.
The third stage is the actual measurement: a flash flood washed the ground, and they collected 40 L water samples with a total mass of 40.56 kg. The previously measured dry sediment density is 2.4×103 kg/m3/m3, so the average sediment concentration in the flood is calculated.
(1) Please take part in the work of the first stage of the environmental protection team, deduce the relationship between ρ muddy water and ρ water, and ρ sand and X, and then draw an image sketch of the change of sediment water density ρ with sediment concentration X according to the relationship.
(2) Please participate in the calculation of the third stage of the environmental protection team and work out the average sediment concentration in the flood.
6.( 10) The main advantage of the popular digital camera is that it can directly generate digital photos, which is convenient for editing and processing and lasts longer. In addition, digital photos can be displayed directly on the computer or sent by email.
On the right is some information about digital camera batteries.
According to the information provided on the right and the following introduction to the working process of digital camera, answer the relevant questions:
(1) The digital camera will be in standby state after being turned on, which will consume a certain amount of electricity. When shooting, shooting and processing data consumes a lot of power. Suppose that a fully charged battery is used as the power supply and a photo is taken every 5 minutes. The average working current of the camera is 0.2A Please estimate the maximum number of photos that can be taken with a fully charged battery.
(2) What is the efficiency of fully charging a battery that has been completely exhausted?
7. (12 minutes) The "number" of the air conditioner is an approximate representation of the input power of the air conditioner. Because the refrigeration efficiency of air conditioners of the same model and different brands is quite different, for the convenience of comparison, the efficiency of air conditioners is often expressed by "refrigeration capacity".
When choosing an air conditioner, besides the cooling capacity and heating capacity (cold and hot air conditioning), we should also consider the "energy efficiency ratio".
The energy efficiency ratio of the air conditioner is =, indicating whether the air conditioner is efficient and energy-saving. At present, the energy efficiency ratio of air conditioners in the market varies greatly, generally between 2 and 3, and the highest can reach about 3.5. We should try to choose air conditioners with high energy efficiency ratio.
The required cooling capacity and heating capacity of a room can be calculated according to the following formula: cooling capacity Q cold =S (room area) ×140 w-180 w; ; Heating capacity q heat =S (room area) × 180 w-240 w (this formula is applicable to rooms with a floor height of 2.5 m. If the floor height is too high, the power should be increased appropriately).
The following table is part of the operating instructions of a certain type of air conditioner that Xiao Ming's family is going to buy.
Please combine the knowledge introduced above with the instruction manual of air conditioner and answer the following questions through calculation:
1. What is the energy efficiency ratio of this air conditioner?
Xiaoming's newly bought building has a living room with an area of about 30m2 and a height of 2.7m He wants to install the air conditioner shown in the above table in the living room. Please explain whether this choice is reasonable through calculation.
3. If Xiao Ming uses this air conditioner for refrigeration, the compressor of the air conditioner actually works for 6 hours every day. How much is the electricity bill for only one air conditioner per month? (The local electricity price is 0.5 yuan/kWh)
8.( 12) On the wall of Xiaojun's living room, there is a switch for controlling the lighting and an electrical component installed with two holes. Figure 12 is the panel of the module, and figure 13 is the original wiring diagram inside the module shell. Because the switch is broken, the whole part needs to be replaced. Xiaojun's father decided to finish it by himself, and Xiaojun was his assistant.
Xiaojun's father turned off the main switch of the home access line, and in the process of replacing the old one with the new one, he found that he did not pay attention to the connection relationship between the three lines A, B and D (there is a short line between B and C) and the outside three lines (as shown in figure 14). Because the indoor wires are all in the cement wall, it is impossible to observe the connection between the wires in the wall.
So he turned off the main switch of the home circuit and detected each wire with the electric probe, and found that: ① the first wire can make the electric probe glow; The second and third wires can't make the electric pen glow.
According to Xiaojun's father's test, can you judge the connection of each wire? After careful consideration, Xiaojun believes that it is impossible to judge the connection of each conductor. If the connection is blind under unknown circumstances, more serious problems may occur.
(1) Do you think Xiaojun's point of view is correct? Why?
(2) Can common household appliances, such as desk lamps (all with plugs) be used to identify how wires should be connected to terminals A, B and D respectively? Tell me your method and briefly explain why.
(3) According to your judgment, connect the line 12③ in Figure 14 with the terminals A, B and D below and the live wire, zero line and light bulb above.
The 16th National Junior High School Applied Physics Competition
Reference solution and grading standard
Description:
1. Except for multiple-choice questions, the provided reference answers are not necessarily unique and correct. For those different solutions, the correct one will get the same score.
2. The grading standard is only given according to an idea and method. In the process of marking papers, there will be various situations. Specific measures can be formulated according to the spirit of this scoring standard, but there should be no big deviation from this scoring standard.
3 Questions and answers or calculation questions are graded according to the step-by-step method. In the grading standard, (1) and (2) are often written ... The formula here is used to represent the steps. If the candidate does not write this formula, but embodies this step in the process of writing expression or later problem solving, the score is the same. If you don't write any formula or text description and only give the final result, you can't score.
4. The numerical results in the reference solution are given according to the operation requirements of significant figures, and there is no requirement for candidates. Don't deduct points because of errors in valid figures.
5. In the final award, if the number of people with the same score exceeds the number of winners, it is difficult to select, and the papers to be selected can be judged by adding points. The basic basis for judging extra points is:
(1) The method or principle used is not what the textbook says, and it is innovative and worthy of extra points;
(2) The method is simple, and extra points should be added;
(3) Put forward a variety of correct solutions, which should be supplemented;
(4) The test paper is clear and can make full use of mathematical tools, so extra points should be given.
The implementation of the above-mentioned projects shall be stipulated by the competition leading group (the unified allocation of reward places in the province shall be decided by the province, and the allocation of reward places at the prefecture level shall be decided by the prefecture level).
A, multiple-choice questions each small 3 points, *** 15 points.
1.C (3 points) 2. C(3 points) 3. B (3 points) 4. B (3 points) 5. C(3 points)
Second, fill in the blanks *** 15 points
1 before. (3 points) (1 minute); After that (1 min); Shun (1)
2.(3 points) C( 1 minute); b( 1)； Province (1 min)
3.(3 points) When the air pressure is low (or lower than 1 standard atmospheric pressure), the boiling point of water decreases (or lower than 100℃)(2 points); Big (1)
4.(3 points) less than (1 minute); Less than (2 points)
5.(3 points) (1) along a straight line (1 min); (2) timbre (1); (3) Red, green and blue (1)
Three. Short answer ***22 points
1.(4 points) Reference answer:
(1)(2 points) The huge white air mass is composed of small water droplets. .................................................................................................................................................
It is formed by vaporizing the water in the pool and then cooling and liquefying it into small water droplets floating in the air. .................. 1 point
(2)(2) The high-temperature flame is sprayed into the water, and the water absorbs heat and vaporizes into water vapor, thus protecting the launch pad.
Water can also reduce the shock absorption effect, which is also a protective effect. If you don't answer this question, you won't be penalized.) ....................... scored 2 points.
2.(4 points) Reference answer:
(1) Glaze the surface of insulator to make it smooth and prevent it from conducting electricity due to dust and dirt accumulated in the air for a long time; .........................., two points.
(2) The purpose of making the joint shape is to increase the length of the surface layer that may leak electricity, thereby increasing the resistance of the insulator and reducing the risk of leakage. ..... 2 points
3.(4 points) Reference answer:
As shown in the answer sheet 1, when the filament of the small colored lamp L burns, an open circuit is formed between AB, and a voltage of 220V is directly applied between the thin metal wire and the filament conductive bracket AB; ............................................., two points.
The oxide layer is broken down, and the thin metal wire is connected with the filament conductive bracket. At this time, this light is only equivalent to a piece of wire (as shown in the answer sheet 1), which plays the role of connection and allows other small colored lights to continue to work. ......................................, two points.
But the voltage on each lamp has risen a little, but it is not enough to burn out the filament. Of course, if too many small lanterns are burned, other small lanterns will be burned because of the high voltage. (No points will be deducted if you don't answer this paragraph)
4.(4 points) Reference answer:
As shown in figure 2.
Note: ① The connected circuit can only control the south or north speakers, and the score is1; All right, four points.
(2) this question does not consider the impedance of the output.
5.(6 points) Reference answer:
① The use of hollow cement bricks reduces the amount of cement and sand, which can effectively save resources.
(2) Building a wall with hollow cement bricks, because the air in the wall is a poor conductor of heat, this house is warm in winter and cool in summer, saving energy.
③ It has sound insulation function.
(4) No clay digging, no environmental damage.
Note: Answer 2 points for each question, with a maximum of 6 points.
Four, (* * * 6 points) reference solution:
According to the meaning of the question, 1 yuan can buy 2 kwh of electricity or 15kg/60=0.25kg liquefied gas ................................................... 1 min.
When electricity is used to boil water, the effective heat obtained by consuming 1 yuan is 2× 3.6×106j× 90% = 6.48×106j.
Consumption 1 yuan The effective heat obtained by boiling water with liquefied gas is: 0.25 kg× 4.2×107j/kg× 30% = 3.15×106j ... two minutes.
Consumption 1 yuan, using electricity to boil water can get more effective heat than using liquefied gas, so using electric kettle to boil water is more economical.
..................................... 1 min.
Other solutions, as long as they are correct, will be graded with reference to the above grading standards.
Verb (abbreviation of verb) (***8 points) Reference solution:
(1) If the sediment concentration is X, the mass of sand is xV, and the volume of sand is.
The volume of water is; The quality of water is:
The total mass of water and sand is:-2 points.
Density of sediment water: = =
Then order. .................. 1 min.
The density of sediment water varies with the sediment concentration x, as shown in answer sheet 3. ............................................................................................................................................................
(2) Basis: then x =.................... 1 min.
Known rho sand = 2.4× 103kg/m3.
Kg/m3
So k = ..................................................1min.
X = kg/m3 ............................ 1 min.
Six, (* * *10) reference solution:
(1) Energy stored when the battery is fully charged.
E = UIT = 3.7V× 2200×10-3a× 3600s = 29304J .........................................................., 3 points.
The average energy consumption of each photo is e1= u1i1t1= 3.7v× 0.2a× 5× 60s = 222j. ......................................................................................................
Number of photos taken n = e/e1= 29304j/222j =132 ..............................1min.
⑵ When the battery is fully charged, the charger outputs electric energy to the battery.
w = u ' it ' = 4.2v×2200× 10-3a×2.5×3600s = 83 160j ..............................................................................................................
Charging efficiency η = e/w = 29304j/83160j = 35.2%. ..................................................................................................................................
Seven, (* * *12 points) reference solution:
1. The energy efficiency ratio of this air conditioner is 2 points.
2. The required cooling capacity is: q-cold = s×140 w-180 w = 30x140 w-180 w = 4020 w. ......................................................................................
The required heating capacity is: qheat = s×180 w-240 w = 30×180 w-240 w = 5160 w. .........................................................................................................
Look-up table shows that the rated cooling capacity of air conditioner is 5000W, and the customized heating capacity is 5300W, both of which are slightly larger than the cooling capacity and heating capacity required by the room. Considering that the building height is 2.7m >: 2.5m and the power should be increased appropriately, this choice is reasonable. .........................., 3 points.
3. The electric energy consumed by the air conditioner in one month is W = Pt = (8.6× 220×) W× 6h× 30 = 340.6 kW h, that is
The electricity fee payable is 340.6 kWh ×0.5 yuan/kWh = 170.3 Yuan .............................. 1 min.
Other solutions (365438+ 0 days per month), as long as they are correct, will be scored with reference to the above scoring criteria.
Eight, (* * *12 points) reference solution:
1. Xiaojun's point of view is right. ..................................... 1 min.
The first wire can make the electric probe glow, which means it is a live wire and must be connected to B; Lines (2) and (3) can't make the electric pen glow, which means it's not a live wire, but we can't tell which line is directly connected to the zero line and which line is connected to the light bulb. If you connect it blindly, you may connect the zero line to D and close the switch to form a short circuit, which may cause a fire and cause a more serious accident. ..... 3 points
2. There are two possibilities for specific connection methods.
(A) the first possibility
Method: Turn off the switch of the desk lamp. If the wires ① and ② are carefully connected to the plug of the desk lamp (do not short circuit), the desk lamp will glow normally. When wires ① and ③ are connected to the plug of the desk lamp, both lamps emit light, but they do not emit light normally, and the brightness is dark, indicating that wire ② is directly connected to the zero line and connected to A; The wire ③ is connected to the light bulb and D.3..
The reason is: when the desk lamp is directly connected to the live wire and the zero wire, it will glow normally; When connected in series with a light bulb, the power of both lamps is less than the rated power, and both lamps are dim. Two points.
The actual connection is shown in Figure 4. Three points
(2) the second possibility
Methods: Close the switch of the desk lamp and carefully connect the wires ① and ② to the plug of the desk lamp. Both lights shine, but they are not normal and the brightness is dark. When the wires ① and ③ are connected to the plug of the desk lamp, the desk lamp will glow normally. This shows that the conductor is directly connected to the zero line and connected to A; The wire ② is connected to the bulb and D .. ................................., 3 points.
The reason is: when the desk lamp is directly connected to the live wire and the zero wire, it will glow normally; When connected in series with a light bulb, the power of both lamps is less than the rated power, and both lamps are dim. ............................................., two points.
The actual connection is shown in Figure 5. Three points
Note: Students can get full marks as long as they answer one possibility correctly.
The seventeenth session has not yet.