Examination questions of national junior high school physics competition

First, multiple-choice questions:

(04 Lishui Nature, Zhejiang Province) The following figure is a schematic diagram of the access circuit of the sliding rheostat, in which (c) the resistance of the access circuit cannot be changed by moving the slider.

Dalian, Liaoning (04) Every holiday night, many tall buildings are decorated with thousands of light bulbs. The lighted bulb reflects the outline of the building and looks beautiful and spectacular. These bulbs are (a)

A. Parallel connection B. Series connection

C. it can be connected in series or in parallel. D. it is impossible to judge.

(04 Taizhou) The following data is closest to the truth (A)

A.the quality of an egg is 50gb. The speed of human walking is 5 m/s.

C. The bath water temperature is 70℃ D. The current of the household desk lamp is 1A when it works normally.

. (04 Chongqing) In the circuit shown in Figure 2, the voltage U is constant, and after the switch K is closed, the following results are obtained.

The correct one is (a)

A. the reading of ammeter increases.

B. the reading of ammeter drops.

C. the reading of voltmeter increases.

D. the reading of the voltmeter drops.

. (04 Chongqing) As shown in Figure 4, two light bulbs are connected in series in the circuit. After closing the switch, it was found that one of them was luminous and the other was not. The following statement is true (b)

A. the filament of the non-luminous bulb is broken

B. Compared with these two kinds of lamps, the filament resistance of non-luminous bulbs is smaller.

C the voltage across the non-luminous bulb is larger than that across the two lamps.

D. Compared with these two lamps, the current passing through the non-luminous bulb is smaller.

(04 Guiyang Experimental Zone) Which of the following statements is the characteristic of parallel circuit (C)?

A. the currents in all parts of the circuit are equal. Any break in the circuit will lead to an open circuit.

C. the voltages on all branches are equal. The sum of the voltages of all parts of the circuit is equal to the total voltage.

(04 Ningde, Fujian Province) The methods of "controlled variable method", "equivalent substitution method", "model method" and "analogy method" are often used in physics research. The following are some research examples in junior high school physics:

① When an object is subjected to several forces, the concept of resultant force is introduced.

⑦ Use light to indicate the propagation direction of light.

(3) Compare the current with the water flow.

④ The magnetic field is described by magnetic induction lines.

In the above example, (c) adopted the same research method.

A.①③ B.②③ C.②④ D.①④

. (04 Chenzhou, Hunan Province) As shown in figure (1), it is the reading of an ammeter connected to a certain circuit, and the correct reading is (b).

a . 0.32 a b . 1.6A c . 0.26 a d . 1.52 a

. Chenzhou, Hunan (04) As shown in Figure (3), when the switch S is closed and the slider P of the sliding rheostat moves to the right, the indication of the ammeter will be (b).

A. Larger B. Smaller C. Constant D. Uncertain

A, fill in the blanks (this big question 18 points)

1. A car is driving at a constant speed of 36 km/h on the expressway parallel to the railway, and a train with a speed of 54 km/h is approaching. Passengers on the train saw that the train had passed 7 seconds, so they knew that the train was _ _ _ _ _ meters long.

2. When using a pressure thermos bottle, as long as the piston is pressed, the boiling water in the bottle will flow out from the water outlet. This is because the water pressure can be released after _ _ _ _ _ presses the piston.

3. The simplest way to judge whether the lens is convex is _ _ _ _ _ _ _.

4. The force acting on an object falling at a constant speed on an inclined plane is _ _ _ _ _.

5. When choosing the metal wire for manufacturing the light bulb, the part of the metal wire welded in the glass must be the same as that of this kind of glass, so as to ensure a good combination between them.

6. When a classmate saw lightning in the distance and began to remember, he heard thunder after △t time. If it is known that the propagation speed of light in the air is C and that of sound in the air is V, and if C, V and △ T are used to represent the distance S from the place where it thunders, then S = _ _ _ _ _ _ _ _ Because of c v, the above distance can be approximately expressed as S ≈ _ _ _ _ _ _.

7. Any two of the three bulbar balls attract each other, and the condition for charging these three bulbar balls must be _ _ _ _ _ _ _ _.

8. As shown in figure 1, the power supply voltage is stable and the power consumed by the three resistors is equal. If the resistance of R3 increases, the resistance that consumes more power at this time is _ _ _ _ _ _ _.

Second, multiple-choice questions (fill in the serial number of the correct answer in brackets, this big question ***30 points)

1. When a motorcycle flies over a tall obstacle, the first wheel that touches the ground should be [] in order to avoid overturning.

A. front wheel

B. Rear wheel

C. the front and rear wheels should land at the same time.

D. Any landing method is the same.

2. Figure 2 shows the photos taken by the lake. Because the lake is calm, the scenery on the shore is very similar to the reflection in the lake in the photo. Among the following methods, the method that cannot be used to distinguish the real scene from its reflection in the lake is []

A. the reflection is slightly darker than the real scene.

B. The reflection is slightly less clear than the real scene.

C. the left and right positions of the characters in the reflection are opposite to the real positions when taking pictures.

D. The height of the characters in the reflection is slightly larger than that of the real characters.

3. The I-U diagram of the current intensity of two resistors with different resistances varying with voltage is shown in Figure 3. Among the following conclusions drawn from the figure, the correct one is []

A.R 1>R2 .

B. The I-U diagram of the total resistance after R1and R2 are connected in series is in zone II.

The I-u diagram of the total resistance after C.r 1 and R2 are connected in parallel is in zone III.

The I-u diagram of the total resistance of D.R.1and R2 in parallel is in zone I..

4. Kick out the ball weighing 4 cows with the strength of 50 cows, and the ball will roll out 20 meters away and stop. So the work done by kicking is []

A. 1000 joules

Eighty cents

C. 1080 jiao

D. The conditions are not enough to determine

After the astronauts landed on the moon, they could still see a red sun in the sky when they looked up, but the other sights around them should be [].

A. In the dark, you can see the stars, but they don't twinkle.

B.it's dark, the stars are visible and still shining.

C.it's too bright to see the stars.

D. It is sky blue, and you can see the earth and the stars.

6. As shown in Figure 4, the Torricelli experimental device for measuring atmospheric pressure is placed on the electronic scale, and the glass tube A is fixed with a bracket, which does not touch the bottom of the mercury tank B. When the atmospheric pressure is 1.0× 105 Pa, the reading of the electronic scale will be Q, and if the external atmospheric pressure drops, the reading of the electronic scale will be [].

A. greater than q

B. less than q

C. equal to q

D. unable to determine

7. As shown in Figure 5, the experimental vehicle moves at a uniform speed on the horizontal road, and two objects with the mass of m and m are placed on the smooth table fixed in the carriage, m > m ... When the vehicle stops suddenly, the two objects leave the table [].

A. Must collide

B.never collide.

C. Not necessarily colliding

D. Fight first, then part.

8. Four students made on-off detectors to check whether the wires are on or off. It connects a coil, a small bulb, an earphone and an ammeter in series with the dry battery, as shown in Figure 6. When in use, connect P and Q to both ends of the wire to be tested, and judge the on-off situation in the wire from whether the small magnetic needle deflects, whether the small light bulb emits light, whether the earphone clicks, and whether the ammeter pointer deflects. Which of the four detectors do you think is not feasible []

9. As shown in Figure 7, the total resistance of sliding rheostat M is 10 ohm, and the total resistance of sliding rheostat N is 200 ohm. The resistance value of the resistor R is about 20 ohms. In order to slightly increase the reading of the voltmeter, it should be []

A. move the slider of n to the left for a short distance.

B. move the slider of m to the left for a short distance.

C. move the slider of n to the right for a short distance.

D. move the slider of m to the right for a short distance.

10. In daily life, food is stewed in porcelain bowls, and the bowls are not in direct contact with the bottom of the pot. As shown in Figure 8, the water in the pot is boiling, and the soup in the bowl must be [].

It will boil, but it will be slow.

B. Boil at the same time as the water in the pot.

C it will not boil, and the temperature is 100℃

D it will not boil, and the temperature is lower than 100℃

1 1. In most parts of China, the season when you open the refrigerator to see "white fog" is summer, and the season when you see white breath in your mouth is winter. Among the following conditions that produce these phenomena, the wrong one is []

A. It is humid in summer, and the air contains a lot of water vapor, which is one of the former conditions.

B. Summer drought, hot and dry is one of the former conditions.

The gas exhaled by C's mouth contains a lot of water vapor, which is one of the conditions of the latter.

D. dry and cold winter is one of the conditions of the latter.

12. Pour a small bucket of hot water with a temperature of t2 into a large bucket of cold water with a temperature of t 1, and the mixing temperature is t. The correct one in the following relationship about temperature is [].

13. A "220V 1000W" electric furnace, which wants to be modified and connected to the11000 V circuit, does not add other materials and equipment, and the power is still 1000W. The following measures are feasible []

A. cut the electric furnace wire into two sections with the same length and connect them in parallel to form a 1 10V circuit.

B, cut off half of the electric furnace wire and connect it to the 1 10V circuit.

C, cut off 3/4 of the electric furnace wire and connect the remaining 1/4 to the 1 10V circuit.

D cut off the electric furnace wire 1/4, and connect the remaining 3/4 to the 1 10V circuit.

14. In the process of moving the sensitive ammeter, its pointer will swing left and right due to collision or vibration. In order to reduce this swing, the following measures are correct [].

A. Connect the positive and negative poles of the ammeter with wires.

Try to fix the pointer of the ammeter on the dial.

C remove the pointer of the ammeter and store it separately.

Fix the perimeter of the ammeter with foam plastic.

15. Five resistors with resistance values of R are connected to form a quadrilateral ABCD, as shown in Figure 9. The resistance between any two nodes in A, B, C and D cannot be [].

A.R B R/S

C. draft decision ii

Third, the drawing problem (this big problem *** 12 points)

1. The schematic cross section of bicycle pump is shown in figure 10. There is a structure in the picture that is not complete. Please fill in the structure according to the principle and process of air pumping. This kind of pump with small barrel B has the advantages of _ _ _ _ compared with the pump without small barrel B and only with large barrel A.

2. The positions of the sun and the moon are shown in figure 1 1. Please draw a picture of total solar eclipse, partial solar eclipse and annular solar eclipse when people on earth are located in _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

Four. (6 points) In the experiment of measuring the density of brine, the weight used to weigh the quality of salt and the position of the traveling code are shown in Figure 12. Measure pure water with a measuring cylinder, as shown in figure 12. Then the salt is completely dissolved in the water, and the position after the water level rises is shown in C in figure 12. Therefore, the mass of salt is _ _ _ _ _ _ _ grams, and the volume of pure water is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

5.( 10 minute) The lamp will dim at the peak of household circuit power consumption, which is caused by the decrease of voltage at both ends of the lamp. A classmate wants to measure the actual voltage of the home circuit at this time, but he doesn't have an AC voltmeter at hand. It only has a watch, an electric soldering iron with a nameplate, and a running watt-hour meter with a nameplate on the switchboard in the circuit. He used these devices to calculate the actual voltage across the appliances in the home circuit. Please explain his measurement and calculation method.

6.( 12 minutes) A factory designed a water reservoir (as shown in figure 13). The liquid level of the water source tank A remains unchanged, and there is a small water outlet with an area of S 1 at the bottom of the tank, which is connected with the lever BC through a piston with a cross-sectional area of S2. The lever can rotate up and down around the B end, and the other end has a hollow cylindrical float with a sectional area of S3, and BO is 1/3 of the total length of the lever. The original design intention is that when the lever is horizontal, the immersion depth of the float is h2, and the piston can just block the water outlet. However, when the piston is at a very small distance from the water outlet, the float stops floating, and the immersion depth of the float is h3. In order to make the piston automatically block the water outlet, we have to. Try to find out that the weight g' should be subtracted from the float. (Not counting the weight of the piston and connecting rod, not counting the buoyancy of the lever. )

7.( 12 minutes) There are two kinds of light bulbs, which are marked with "1 10V 60W" and "10V25W" respectively, and connected to the lighting circuit at home.

(1) Can one of them be used in series? Please explain the reason.

(2) If two kinds of bulbs are mixed in the home circuit and both can emit light normally, how many bulbs should be used at least and how to connect them?

(3) What is the total power of the light bulb at this time?