Requesting documents: Preliminary test questions for the 19th National Junior High School Applied Physics Knowledge Competition in 2009

2009 National Junior High School Applied Physics Knowledge Competition Test Questions

Notes:

1. Please write your region, school, name and examination number within the sealing line.

2. Write with a blue or black key pen or ballpoint pen.

3. This test paper has seven major questions, with a maximum score of 100 points.

4. Answer sheet time: 9:30-11:10 am on March 29, 2009 (Sunday).

Question number one, two, three, four, five, six, seven, total score

Score

Reviewer

1. Multiple choice questions (each question 2 points, *** 12 points): Only one of the four options given in the following questions is correct. Fill in the letters in front of the correct option in the brackets after the question.

1． Fiber optic networks were installed in all sports venues at the 2008 Beijing Olympics. The main purpose of optical fiber in venues is ( )

A. Electricity transmission b. Communication c. Heat conduction D. Lighting

2. On a hot and windless summer day, Xiaoyu was walking on the sun-scorched asphalt road when he saw that the road in front of him had been soaked by a sprinkler truck. He thought that walking on the wet road must feel cooler than walking on the dry road, so he walked over quickly, but he felt even hotter on the water-sprinkled road. Do you think the main reason for this feeling is ( )

A. After the water in the sprinkler truck is exposed to the sun, its internal energy increases and its temperature is very high

B. The water on the ground causes more sunlight to be reflected, and the body gets more heat

C. After sprinkling water, the humidity of the nearby air increases, and the evaporation of sweat on the body slows down

D. When the water on the ground evaporates, it brings heat to the human body

3. When repairing a punctured bicycle inner tube, the repairman usually uses a file with thorns all over to file the outer surface of the punctured inner tube, and then files the side of the rubber patch that is to be repaired on the inner tube. Then apply glue to the two surfaces of the file. After the glue has dried for a while, align and press it... Regarding the following analysis of the main purpose of filing rubber surfaces, do you think the most likely one is ( )

A. Make the rubber at the tire patch more swollen to enhance the elasticity of the rubber at the tire patch

B. Increase the surface area of ​​contact between the inner tube and the rubber patch to give full play to the adhesive effect of the glue

C. Increase the friction between the inner tube and the rubber patch to prevent misalignment

D. Prevent the uneven pressure of the inner tube against the outer tire due to the thick tire patch, and prevent the outer tire from blowing out

4. Dust accumulates more easily on the exterior surfaces of car carriages than on trains. Regarding the analysis of the causes of this phenomenon, do you think the following statements are most likely ( )

A. The outer surface of a train carriage is smoother than that of a car carriage and is less likely to accumulate dust

B. The train travels faster than the car, and the wind generated is stronger, making it easier to blow away the dust

C. The speed of trains is greater than that of cars. The air flow speed outside the carriage is greater than that of cars. The air pressure outside the carriage is smaller than that of cars. The pressure difference between the inside and outside of the carriage is greater than that of cars, making it less likely to accumulate dust

D. When the vehicle is running, the outer surface of the carriage becomes charged due to friction with the air. Because the tires of the vehicle are insulating rubber, it is not easy to conduct the charge into the ground compared with the trains with iron wheels, so it is easier to absorb dust.

5. During the road construction of cement pavement, one of the processes is to insert a long wooden strip into the cement approximately every 8 meters to cut the cement pavement into pieces. Then, while the cement is not completely solidified, use a toothed wheel to draw horizontal lines on the paved road surface (as shown in Figure 1). Based on the analysis of the following practices, do you think the most likely statement below is ( )

A. Using a toothed wheel to draw horizontal lines on the paved road is to make the road more beautiful

B. Use long wooden strips to cut the cement pavement into pieces in order to save cement materials for paving the road.

C. Use long wooden strips to cut the cement pavement into pieces to prevent damage to the pavement due to thermal expansion

D. Use long wooden strips to cut the cement pavement into pieces in order to increase the friction of the road

6. As shown in Figure 2A, the gas pipeline includes outdoor and indoor parts, and a gas meter is connected between the two parts. After the master workers install indoor pipes for each household, they must check whether the pipes are leaking. There is a detection device as shown in Figure 2B. Water is contained in a transparent U-shaped tube open at both ends. When the pressure at both ends of the U-shaped tube is equal, the water surfaces on both sides will be flat. During the test, after turning off the switch, blow air forcefully into the user pipe mouth Y, and then quickly connect one end Y of the U-shaped pipe to the user pipe mouth Y. A height difference will appear in the water surface in the U-shaped pipe (as shown in Figure 2C).

Observing the changes in the water surface in the U-shaped tube can determine whether the indoor pipeline is leaking ( )

A. If the height difference of the water surface gradually increases, it indicates that there is no air leakage

B. If the height difference of the water surface gradually decreases, it indicates that there is no air leakage

C. If the height difference of the water surface remains unchanged, it indicates air leakage

D. If the height difference of the water surface remains unchanged, it means there is no air leakage

2. Fill in the blanks (2 points for each question, ***6 points)

1. Scientists infer that the universe is expanding based on the red shift phenomenon of the planet's spectrum, and the planet is getting farther and farther away from us. In fact, there is a similar phenomenon in sound in daily life. When the train rushes past us, although the frequency of the whistle emitted by the train remains unchanged, the pitch of the sound we hear is (optional "changes from high to high"). "low" or "from low to high")

2. At 14:28 on May 12, 2008, a strong earthquake measuring 8.1 on the Richter scale occurred in Hanchuan County, Sichuan Province, my country. In order to provide timely understanding of the earthquake The disaster situation in the area was analyzed to facilitate command and dispatch. Relevant departments used aircraft aerial photography and satellite remote sensing technology. Aerial photography can only be done during the day and uses visible light reflected from ground objects. During the shooting process, the image of objects on the ground on the camera should be between one and two times the focal length of the camera lens, and closer

(Optional "one focal length" or "Double focal length"); while satellite remote sensing can work around the clock, because it can not only sense visible light, but also the (optional "ultraviolet" or "infrared") emitted by objects.

3． When building high-rise buildings, most of their foundations use box foundations. The so-called box foundation is to hollow out the entire building's land and then fill it with reinforced concrete. The advantages of the box-type foundation are: first, it increases the contact area between the building and the ground, thereby reducing the resistance of the building to the ground, which can effectively prevent substantial subsidence of the land; second, it reduces the resistance of the entire building and increases It increases the stability of the building and improves the building's earthquake resistance.

3. Briefly answer the following questions (5 points each. ***30 points)

1. Tofu is originally smooth and tender (as shown in Figure 3A). After freezing and thawing, many small holes will appear, turning into delicious "frozen tofu" (as shown in Figure 3B). Please explain the meaning of "frozen tofu". The reason why many small holes are produced.

2． After Xiao Ming learned about household circuits, he paid more attention to observing household appliances in his life. He found that his washing machine used a three-pin plug, and the plug was marked with some symbols and words, as shown in Figure 4.

(l) Please write the meaning of the following logos or characters: ① 10A250V ② E; ③ L; ④ N.

(2) Xiao Ming carefully observed the three pins and made a new discovery: the pin marked with "E" is slightly longer than the other two pins. He checked the three-pin plugs of other electrical appliances and found the same situation. Please write down the benefits of making it this way from the perspective of safe electricity use.

3． Xiaolin's home has a new electric water heater installed. There is a warning as shown on the right next to the nameplate of the electric water heater. Please use the physics knowledge you have learned to give a reasonable explanation for the necessity of this warning.

4. Figure 5 shows a platform scale commonly used in stores to weigh goods. Try to analyze whether the weighing result is too large or too small compared with the actual weight when weighing goods under the following circumstances. (l) The weighing scale is worn: (2) The position of the zero adjustment nut is screwed further to the right than the correct position.

5． As shown in Figure 6A, three identical wires are threaded through a hard plastic pipe spanning both sides of the river. In order to identify which two wire ends are the two ends of the same wire, the master worker uses the "pass tester" shown in Figure 6B to conduct the test. He first connected A and B, then connected m of the "pass tester" to D and n to F, and found that the small light bulb glowed at this time... What judgment can the master worker make based on this? What will he do next to finally figure out where each wire ends?

6． Xiao Ming moved into a newly renovated new home, and his mother bought him a bedside lamp. He plugged the bedside lamp into the socket on the wall next to his bed. At night, when Xiao Ming was reading in bed, the bedside light suddenly went out. After a while, the light came on again. At this time, he found that his father had just walked out of the bathroom after taking a shower. Xiao Ming was very curious, so he went to the bathroom to turn on the light of the "bath heater" and found that the light on his bedside went out again; when he turned off the light of the "bath heater", the light on the bedside turned on again. Xiao Ming wanted to know why his bedside lamp had this "strange phenomenon" and what was wrong with the wiring?

(1) Please draw the circuit diagram connecting the bathroom heater lamp and the bedside socket (bedside lamp) when decorating Xiao Ming's home, and use the knowledge you have learned to analyze the cause of this "strange phenomenon".

(2) If you do not want the above "strange phenomenon" to occur and the bedside lamp switch can control the bedside lamp on and off normally, please draw the correct circuit diagram.

4. (10 points) In order to alleviate the contradiction of power shortage during peak electricity consumption, some areas in our country use "time-of-use electricity (energy) meters".

The following table is the electricity price list before and after time-of-use billing is adopted:

Original meter billing method Time-of-use meter billing method

Time range peak period and trough period throughout the day

p>

6:00～22:00 22:00～6:00 the next day

Unit price (yuan/degree) 0. 48 0. 50 0.30

Xiao Mingjia An electric kettle is used to boil water with a mass of 3kg and an initial temperature of 20°C every day. It is known that the air pressure is l standard atmospheric pressure and the specific heat capacity of water is 4.2×103J/(kg?°C). Find:

1. How much heat does it take to boil this water?

2. After using the time-sharing meter, Xiao Ming's family arranges the water boiling time during the low period. If heat loss is not included, how much electricity bill will be saved in one month (based on 30 days) compared with the original one?

5. (14 points) Figure 7 shows a solar lighting lamp. The solar panel supplies one "220 V 40W" electronic energy-saving lamp to work. If the effective area of ​​the solar panel to receive solar energy is 0.3m2, the solar radiation energy received by the surface perpendicular to the sunlight at that point on the earth is about 7.2×104J/(min?m2). The sun shines for one day, which is enough for electronic energy-saving lamps. Work for 10 hours. Assuming that the sun is always shining vertically on the solar panel and does not consider the influence of weather, it is calculated as 8 hours per day. Request:

1. What is the approximate efficiency of solar lighting using solar energy?

2. If a 200W incandescent lamp has the same luminous effect as this 40W electronic energy-saving lamp. Please calculate and explain based on the data in the table below: Is there an economic advantage to using this kind of solar lighting compared to using this kind of incandescent lamp at the current price? (The lamp works 10 hours a day, and is calculated as 365 days a year)

Rated voltage/V Rated power/W Average lifespan Selling price per unit Electricity charge per kilowatt-hour

Incandescent lamp 220 200 1000 hours 2.0 yuan 0.5 yuan

Electronic energy-saving lamp 220 40 8000 hours 20 yuan

Solar panel 1500 yuan 20 years

6. (14 points) Technology team The students want to use the buoyancy knowledge they have learned to make a buoyancy scale. They found an empty beverage bottle with a cylindrical body, cut off the bottom, tightened the cap, tied a stone of appropriate quality to the cap, and then placed it upside down in a bucket, as shown in Figure 8. When using it, just put the object to be measured into the bottle, and the mass of the object to be measured can be read directly from the scale facing the water surface.

1． What is the purpose of the stones here? Try to apply the physics knowledge you have learned to analyze the rationale.

2. Is the mass scale of this buoyancy scale uniform? Why?

3. After measurement, the diameter of the cylindrical part of the beverage bottle is 8.0cm. When the measured object is not placed in the buoyancy scale, the position facing the water surface is zero scale (as shown in Figure 8). Please calculate the corresponding mass value for the buoyancy scale on the right side of each scale line 1, 2, 3, and 4 based on the length values ​​marked in the figure. (π is 3.1, and only integers are retained in the final result)

7. (14 points) The biogas digesters built in some rural areas obtain biogas by fermenting a large amount of straw and human and animal excrement in the countryside, and utilize biogas Come and make a fire to cook and light a lamp for lighting. The application of biogas digesters not only enables better utilization of the above resources, but also brings many conveniences to life and improves the environment. This is a project that benefits the people with multiple benefits. Figure 9 shows a schematic cross-sectional view of a farmer's hydraulic biogas digester.

Instructions: 1. Biogas digester 2． Hydraulic pool 3． Feed port 4. Sealing cover 5. Gas pipe 6. Air storage chamber 7. Biogas pressure indicator 8. Main valve 9. U-shaped tube pressure gauge (containing water dyed red) 10. Discharge port cover (the hydraulic pool is not sealed. The hydraulic pool is still connected to the outside atmosphere) 11. Valve

It is known that the relevant technical data of the farmer's gas stove are as follows:

Used fuel: liquefied petroleum gas, natural gas, artificial coal gas, artificial biogas

Pressure in front of the stove (kP a) 2.8 2.0 1.0 1.5

Rated heat flow

(kW) Ordinary furnace left: 3.6 Combination furnace left: 3.6

Right: 4.0 Right: 3.6< /p>

Single furnace 4.0

Suppose g=10 N/kg, the specific heat capacity of water c water=4.2×103J/(kg?℃)

1. According to the calculation shown in Figure 9, can the farmer use the biogas in this biogas digester to cook normally?

2. One day, the farmer discovered that the biogas pressure was lower than the requirements for the gas stove. From a physical point of view, what measures can be taken to make use of biogas for cooking as quickly as possible?

3. If the gas stove used by the farmer is an ordinary stove, under normal circumstances, when the right stove in the ordinary stove is working normally alone, it takes about 10 minutes to boil a pot of water with a mass of 2.5kg and a temperature of 20°C.

Try to estimate the water boiling efficiency of the right furnace.

4. Please share your thoughts on how to improve the efficiency of gas stoves.

Reference solutions and scoring standards for the 2009 National Junior High School Applied Physics Knowledge Competition

1. Multiple-choice questions (2 points for each question, ***12 points)

1. B 2. C 3. B 4. D 5.C 6.D

2. Fill-in-the-blank questions (2 points for each question, ***6 points)

1. From high to low (2 points) 2. Double focal length, infrared (1 point for each empty space, ***2 points)

3. Pressure, center of gravity (1 point for each empty space, *** 2 points)

3. Short answer questions (5 points each, ***30 points)

1. (5 points) Reference answers

There are three Key points: (1) After water freezes, its volume will increase. (2) Tofu contains water. After freezing, the small ice cubes in the tofu squeeze the whole piece of tofu into a honeycomb shape. (3) After the ice melts into water, many holes are left.

Explanation: Points (1) and (2) are worth 2 points each, point (3) is worth 1 point, and *** is worth 5 points.

2. (5 points) Reference answer

(1) ①The maximum safe current allowed by this plug is 10A, and the maximum safe voltage it can withstand is 250V; ②Ground wire; ③Live wire; ④Neutral wire

(2) There are three key points: ①The grounding pin is slightly longer than the other two pins, so that when the plug is inserted into the socket, the metal shell of the electrical appliance is grounded first. Then the electrical appliance is connected to the live and neutral wires; ② When the plug is unplugged, the electrical appliance is now disconnected from the live and neutral wires, and finally the metal shell is separated from the ground wire. ③ Ensure that when inserting and unplugging the plug, even if the outer casing of the electrical appliance "leakage", no electric shock will be caused.

Explanation: (1) 0.5 points each for ①, ②, ③, and ④, ***2 points; (2) 1 point each for key points ①, ②, and ③, ***3 points.

3. (5 points) Reference answer

There are three key points:

(1) Because daily water is not pure water and contains impurities, it will conduct electricity and wet the water. Pulling and plugging the power plug by hand may cause electric shock.

(2) If there is no water in the water tank, the temperature of the water heater will continue to rise rapidly after power is turned on, until the water heater is damaged.

(3) In the cold season when the temperature is below 0°C, if the water heater is stopped for a long time, the water in the water heater will become larger due to freezing, and it is easy to burst the water heater.

Explanation: Points (1), (2), and (3) are 2 points each, and point (3) is 1 point.

4. (5 points) Reference answer

(1) If the weight is worn, the weight must be placed at a position where the scale is too large when weighing, so that the scale can be balanced, so The weighing result is too large compared to the actual weight.

(2) If the position of the zero-adjusting nut is screwed further to the right than the correct position, an object of a certain mass needs to be placed in the scale pan to balance the scale when the weight points to zero. Then put the goods to be measured on the scale pan. When balanced, the mass of the goods is equal to the weighing mass. At this time, the weighing mass is less than the sum of the masses of the two objects in the scale pan, so the weighing result is smaller than the actual mass.

Explanation: (1) 2 points, (2) 3 points.

5. (5 points) Reference answer

There are three key points:

(1) Make sure C and E are two ends of the same wire.

(2) In order to find out the two ends of the other two wires, A and C can be connected. One end of the pass tester must be connected to E. If the other end is connected to F and the small bulb glows, then BD is The same wire, AF is the same wire; if there is no light, AD is the same wire, and BF is the same wire. (You can also connect the other end to D. If the small bulb lights up, then BF is the same wire and AD is the same wire; if it does not light up, then AF is the same wire and BD is the same wire.)

6. (5 points) Reference answer

(1) The circuit in the wall was wrong during decoration. As shown in the picture, when the switch of the bathroom "bath heater" light is turned off , the bedside lamp switch is closed, the "bath heater" lamp and the bedside lamp are connected in series, because the "bath heater" lamp has the same rated voltage as the bedside lamp, and the rated electric power of the "bath lamp" lamp is much greater than the rated electric power of the bedside lamp, so The filament resistance of the "bath heater" lamp is much smaller than the filament resistance of the bedside lamp. When the "bath heater" lamp is connected in series with the bedside lamp, the electrical power of the "bath heater" lamp will be much smaller than that of the bedside lamp and will hardly emit light, while the bedside lamp is close to Glow normally.

(2) If you do not want the above strange phenomenon to occur, the bedside lamp switch can control the bedside lamp on and off normally. The correct circuit diagram is as shown in the figure.

Instructions: In (1), drawing the picture to answer -1 is worth 2 points, writing the description is 2 points, ***4 points; in (2), drawing the picture to answer -2 is worth 1 point.

IV. (10 points) Reference Answers

1. This water needs to absorb heat: Q = cm ( )……………………………… …(1 point)

=4.2× ×3×(100-20)J…………………… (1 point)

=1.0× J… ……………………………………………(1 point)

2. 1.0× J＝0.28 degrees……………………………… …………………………….(2 points)

You can save electricity bills: 0.28 × (0.48-0.30) × 30 yuan……………………………… …(4 points)

＝1.5 yuan........................ ...........(1 point)

V. (14 points) Reference Answers

1. The solar panel absorbs energy after working for one day (calculated as 8 hours) Solar energy

E＝7.2× ×0.3×8×60J≈1.04× J…………………………………………(2 points)

The electric energy consumed by the lighting lamp when working for 10 hours

W＝Pt＝40×10×3600J＝1.44× J…………………………………………(1 point)< /p>

＝ 14%……………………………………………………(2 points)

2. In the same time ( 20 years) for comparison:

Total working time of incandescent lamps (or energy-saving lamps): 20×365×10h=73000h

Use of incandescent lamps:

The number of lamps needed is 73000/1000=73 (lights)…………………………………………(1 point)

The cost of purchasing incandescent lamps is 73×2.0 yuan= 146 yuan…………………………………………(1 point)

Electric energy consumed by incandescent lamp

W=Pt=0.2×73000 kW ?h＝14600 kW?h

The electricity bill to be paid is 14600 × 0.5 yuan = 7300 yuan

*** Calculated cost: 146 yuan + 7300 yuan = 7446 yuan………… ………………………………(1 point)

Use of solar lighting:

The number of lights required is 73000/8000=10 (lights)… ……………………………………………(1 point)

The cost of purchasing energy-saving lamps is 10×20 yuan = 200 yuan……………… …………(1 point)

*** Calculated cost: 1,500 yuan + 200 yuan = 1,700 yuan…………………………………………(1 point)

7446 yuan>1700 yuan……………………………………(1 point)

This shows that using this kind of solar lighting is more expensive than using this kind of Incandescent lamps have great economic advantages. …………(1 point)

6. (14 points) Reference Answers

1. The function of the stone is to make the buoyancy scale float vertically in the water. …………………………..(1 point)

The gravity on the stone is much greater than the gravity on the empty drink bottle, so the center of gravity of the buoyancy scale is lower and lower than the buoyancy When the buoyancy force is equal to gravity, the buoyancy scale will float vertically in the water. (If there are no stones, the center of gravity of the entire device will be higher than the point of action of buoyancy. Under the action of buoyancy and gravity, the buoyancy scale will easily tip over and find it difficult to float vertically in the water.)…………………… ……………………………………………(2 points)

2. The mass scale is uniform. ……………………………………………………………….(1 point)

Suppose the mass of the object to be measured is m, and the radius of the cylindrical part of the beverage bottle is r, after placing the measured object in the buoyancy scale, the depth of the bottle immersed increases by h, then:

When the buoyancy scale floats again, the increased buoyancy is equal to the increased gravity: …… …………(1 point)

That is: ………………………………………………………(2 points)

Available : …………………………………………………………………… (1 point)

Because, , and r are constant values, so h is proportional to m, The mass scale of this buoyancy scale is uniform. ………………………………………………………………………… (1 point)

3. Because, so………… ………………(1 point)

Where=1.0× kg/, r=4.0cm, 1cm, =2cm, =3cm, =4cm.

By bringing in the above data, it can be seen that the mass values ​​corresponding to the scales 1, 2, 3, and 4 should be marked as 50g, 100g, 150g, 200g,……………… ………………………………………………(4 points)

VII. (14 points) Reference answers

1. Biogas pressure in front of the stove………… ……………………………………………(1 point)

=1.0× …(1 point)

Because p＞0.5kPa, therefore The biogas in this biogas pool can be used for normal cooking. ………………(1 point)

2. Measures that can be taken are:

Add water and materials into the biogas tank through the feed inlet or add water to the hydraulic tank. wait. If you add an appropriate amount of hot water to the biogas digester through the feed port, the effect will be better.

Note: Each correct and reasonable measure is worth 1 point, up to 2 points.

3. Generally speaking, when the gas stove is working normally, the combustion of gas is very complete, and we can regard it as complete combustion of gas; then the atmospheric pressure at that time is regarded as 1 standard atmosphere.

Heat absorbed by water: △………………………………………………………………(1 point)

=4.2× ×2.5× (100-20) J＝8.4× J………………(1 point)

The heat released by the gas stove: ……………………………… ………………(1 point)

＝4.0× ×10×60J＝2.4× J……………………(1 point)

Right furnace Efficiency of boiling water: = ×100%…………………………………………(1 point)

= ×100%=35%………… ………………………(1 point)

4. The ideas for improving the thermal efficiency of gas stoves are as follows:

Appropriately select stoves with larger rated heat flow to shorten the heating time. time, thereby shortening the time for heat dissipation to the environment to reduce heat loss; promptly remove scale at the bottom of the kettle to speed up heat transfer; when boiling water, it is best to cover the kettle.

Note: Each correct and reasonable idea is worth 1 point, up to 3 points.