Exercises of voltage and current in junior high school physics

Exercises of voltage and current in junior high school physics

Review exercises of physics for Grade 8 of 2006 autumn final examination (Part 1) (5)
(Chapter 5 current and circuit)
: class No.: Name:
1、 Fill in the blanks
1. According to Rutherford's theory of atomic planet model, it is ()
A. Neutrons. B. protons. C. electrons. D. nuclei
2. As shown in the figure, steel and rubber are used to make steel wire pliers for electricians, which are mainly made of steel__________ And rubber__________ The jaw of the steel wire pliers is very thin, so that__________ .
3. After learning the knowledge of series and parallel circuits, Xiaowen asked, "what is the connection between TV sets, lights, fans and other electrical appliances at home
"Parallel connection, of course," Xiaoling replied. What phenomena can explain that they are parallel connection?
(for example);
4. The two light bulbs in figure a are____ (fill in "series" or "parallel") and the water flow in Figure B can be used to simulate the circuit___ (select "voltage", "current" or "resistance")
5. The following table shows the current values of some electrical appliances. Electrical appliances 1, 2 and 3 may be desk lamp, calculator or rice cooker. Then desk lamp should be electrical appliance and calculator should be electrical appliance. Rice cooker works by using the effect of current. Charging mobile phone is to convert electric energy into electricity?
Appliance 1 appliance 2 appliance 3 mobile phone charger
100μA 0.2A 3A 120mA
6. As shown in the figure, several common components and their symbols in the circuit are drawn. Please draw the symbol of the component in the blank space corresponding to the component in the figure
7. There is a process called "carding" in the textile mill. Only after the disordered cotton wadding is combed into straight cotton wadding strips can it be used for spinning. The carding workshop must keep a certain degree of moisture to prevent inconvenience and harm caused by
8. If the charge [quantity] passing through the cross section of a conductor is 40C within 20s, the current passing through the conductor is a
9. What is the indication of the ammeter shown in the figure_______ A.
10. The voltage at both ends of a conductor is 6 v. if the work done by the current on the conductor is 30 joules in 10 seconds, the amount of electricity passing through the cross section of the conductor is 0______ The resistance of the conductor is________ Oh
2、 Multiple choice questions
Class I class II
Copper pencil lead mercury glass wire plastic rod ceramic chip
11. There are six kinds of articles: copper strip, glass filament, pencil lead, mercury, plastic rod and ceramic chip. Xiao Ming divides them into two categories, as shown in the table below. According to which physical properties of substances, Xiao Ming classifies them ()
A. Density B. magnetism C. hardness D. conductivity
12. In the corridor, there are only occasional people passing by at night, and the electric light is always on, which will waste electric energy. Researchers use photosensitive materials to make "light control switch", which will automatically close when it's dark; it will automatically open when it's light. Sound sensitive materials are used to make "voice control switch", which will automatically close when someone walks and make a sound; when no one walks, it will automatically open, It can make the corridor lamp become "intelligent". The correct "intelligent" circuit is ()
13. The following circuit diagram is consistent with the actual diagram ()
14. Generally, the toilet of a family should be equipped with lighting and ventilating fan. Sometimes they need to work independently, sometimes they need to work at the same time
A B C D
15. Lighting and ventilating fan should be installed in the toilet of general family. Sometimes they need to work independently, sometimes they need to work at the same time
16. As shown in the figure, careless Xiaoqiang connected the ammeter to both ends of L1 as a voltmeter. At this time, if the switch is closed, there will be ()
A. Power short circuit B, ammeter damage
C. L1 does not light up, and the filament of D and L2 is burnt out
17. As shown in the figure, two bulbs L1 and L2 with the same rated voltage are connected in series in the circuit. After closing the switch s, it is found that L1 is on and L2 is not. There are several conjectures about this, among which the possible one is ()
① The L2 filament is broken and the lamp holder is not short circuited
② The resistance of bulb L2 is too low
③ The voltage at both ends of bulb L2 is large
④ The current through bulb L1 and L2 is different
⑤ The socket of bulb L2 is short circuited
⑥ The rated power of bulbs L1 and L2 are different
A．① B．①③⑥ C．③④ D．②⑤⑥
18. In the circuit shown in Figure 2 (a), the indication of A1 is 1.2A, and the indication of A2 is shown in Figure 2 (b)
A. The current through L1 is 0.7A B. the current through L1 is 1.2A
C. The current through L2 is 1.2A D. the current through L2 is 2.5A D
19. All the following substances belong to conductor ()
A. Coin, salt water, pencil lead B. rubber, glass ball, coin
C. Glass ball, salt water, pencil lead D. rubber, cooking oil, pencil lead
20. Figure 2 is the schematic diagram of the traffic lights at the intersection. The lights can direct the traffic behavior of vehicles and pedestrians by changing the lights of different colors
A. Red light, yellow light and green light are connected in series. B. red light, yellow light and green light are connected in parallel
C. The red light is connected in parallel with the yellow light and then connected in series with the green light D. the green light is connected in parallel with the yellow light and then connected in series with the red light
21. In the international system of units, the unit of current is
A. Coulomb B. ampere C. Joule D. volt
22. Among the following school supplies, the one that usually belongs to conductor is ()
A. Wooden scale B. plastic pen holder C. metal blade D. drawing rubber
23. There are six kinds of articles: metal knife blade, plastic ruler, 2B pencil lead, salt water, spectacle lens and rubber. Xiao Ming divides them into two categories, as shown in the table below. According to which attribute of the substance does he classify them ()
Class I class II
Metal blade, 2B pencil lead, salt water, plastic ruler, glasses, rubber
A. State B. color C. hardness D. conductivity
24. The following materials are superconductors ()
A. A material whose conductivity is between a conductor and an insulator
B. Materials with high strength and hardness
C. A material with zero resistance when the temperature drops low enough
D. A material made of very small basic units
25. As shown in Figure 7, when the switch S is closed, the bulbs L1 and L2 are not on. When the two ends of a piece of wire contact two points a and B, the two lamps are not on; when the two ends contact two points B and C, the two lamps are not on; when the two ends contact two points c and D, the two lamps are on
A. Lamp L1 open circuit B. lamp L2 open circuit
C. Lamp L2 short circuit D. switch s open circuit
26. In the laboratory, Lu Huizhong found that an ammeter has two ranges, the large range is 0-9a, and the small range is ambiguous. In order to measure the small range, she first uses the large range to connect to the circuit, the pointer position is shown in figure (a), and then uses the small range to connect to the same circuit, the pointer indication is shown in figure (b), then the small range of the ammeter is ()
A、0—0．6A B、0—1A
C、0—2A D、0—3A
3、 Drawing problem
27. As shown in the figure, please connect the circuit elements in the figure with two wires according to the circuit diagram
The components are connected into corresponding circuits
28. As shown in the figure, there is a battery pack, two switches and two lamps. Please connect the following physical circuit diagram to make L1 light when S1 is closed and L2 light when S2 is closed
4、 Experiment and exploration
29. The ninth grade students of Runzhou middle school made their own fruit battery when they were learning the circuit. They inserted copper and iron pieces into the orange, and connected small electric lights between the copper and iron pieces, and the small electric lights glowed: in order to further explore the factors affecting the voltage of fruit battery, the students made a guess, among which
Xiao Wang guessed that the voltage of fruit battery is related to the type of fruit;
Xiao Zhang guessed: the voltage of fruit battery is related to the depth of copper and iron inserted into the fruit;
Xiao Li conjectures that the voltage of fruit battery is related to the distance between copper and iron
Please choose one of the above conjectures to explore and complete the following questions
(1) Write out the steps of the experiment
(2) Design a table for recording experimental data
(3) Before measuring the voltage of the fruit battery, judge the positive and negative poles of the battery. Please write the method of judging the positive and negative poles with a voltmeter
Survey a B C
Current (a) 0.50.20.3
30. The circuit of Xiaoli's inquiry experiment is shown in the figure below. She uses an ammeter to measure the current at a, B and C, as shown in the table below. Please help her to complete the following tasks:
(1) Comparing the data in the table above, we can draw the conclusion that_____________ .
(2) Xiaoli connected the ammeter to point A. when she closed the switch, she found that the pointer of the ammeter was as shown in Figure a. the reason for this failure was that____________ .
31. To measure the current through the small light bulb L1 with an ammeter, three students connected the following circuits a, B and C respectively. Are they connected correctly? If there is any error, please point out where the error is
A： .B：
C： .

Symbols of current source and voltage source

Inside the voltage source symbol is a vertical line, and the current source is a horizontal line, which was first proposed by Einstein,
Inside the voltage source symbol is a vertical line, because the voltage is the potential difference between the two ends of the circuit,
There is potential difference, that is, there is a high end, there is a low end, from high to low = from top to bottom;
Only when there is potential difference between horizontal lines can current be generated,
The current is the product of the balance of the circuit
Later, the International Electrotechnical Commission (IEC) adopted the proposal and formed a regulation

How much resistance is used for 12V led connection
How much resistance does it need to connect a 1w3.5v LED (single) lamp with a 12v12a battery? How can I calculate it in detail?

Current through LED I = P / u = (1 / 3.5A
Resistance voltage ur = 12-3.5 = 8.5V
Resistance R = 8.5 / (1 / 3.5) = 29.75 Ω
Because there is no approximate value of 29.75 ohm resistor, you can choose 30 ohm resistor in series with its LED