I. Choice (2 points for each small question, 40 points for * * *)
1. When you comb your hair with a plastic comb, it will be charged due to friction. After inspection, the charge carried by the plastic comb is negative, so when combing the hair,
A. the plastic comb lost some electrons. Plastic combs get some electrons.
C. the hair gets some electrons. There is no electronic transfer between hair and comb.
2. The following common objects are made of conductor and insulator materials.
3. The following equipment does not belong to electrical appliances.
A. electric lamp B. electric fan C. switch D. rice cooker
4. The battery in the flashlight is placed correctly.
A, A, B, B, C, C and D are all correct.
The street lamps on the road are always turned on and off together. If the filament of one of their lamps is broken, the other lamps can still glow normally. Judging from these phenomena, street lamps are
A. Series connection B. Parallel connection
C. it can be connected in series or in parallel. D. I'm not sure what connection mode it is.
6. In the circuit shown in the figure, after the switch S is closed, the three-lamp area belongs to the series circuit.
7. In order to commemorate and commend scientists for their outstanding contributions to scientific development, their names are often used as countries for scientific measurement in the world.
International unit. The unit of current is named after which of the following scientists?
A. ampere volt ohm watt
8. As shown in the figure, AB and CD are two kinds of metal conductors with different thicknesses made of the same material. Now, they are connected in series in a circuit. Let the current flowing through AB be IAB and the current flowing through CD be ICD, then
A.ICD B . ICD
C.iab = ICD D D. Insufficient conditions
9. The current in a circuit is about 0.4 A, and some students want to measure the current value in this circuit accurately. His current ammeter has two measuring ranges (0~0.6 A and 0~3 A). If he uses the range of 0~3 A, then the result is
A. the current value cannot be measured. The pointer of the ammeter may deflect in the opposite direction.
C. the ammeter may be burnt out. D. the accuracy of the measured value is poor.
10. When the temperature is constant, compare the resistance of two nickel-chromium alloy wires. The following statement is correct.
A. the resistance of long wires is very high. B. The conductor with large cross-sectional area has high resistance.
C. when the lengths are equal, the resistance of thick lines is large. D. when the cross-sectional areas are equal, the resistance of long wires is large.
1 1. The diagram on the right is the schematic diagram of the knob rheostat. If the volume is increased by rotating clockwise, the two terminals should be connected.
A and b, b and c, c and C.
12. according to ohm's law, R = U/I, the correct understanding of it is
A. The greater the voltage across the conductor, the greater the resistance.
B. The smaller the current through the conductor, the greater the resistance.
C. The conductor resistance is directly proportional to the voltage at both ends and inversely proportional to the current passing through.
D. The resistance of a conductor is an attribute of the conductor, which is numerically equal to the ratio of the voltage at both ends to the current passing through the conductor.
13. As shown in the figure, it is a circuit diagram to study the relationship between current and resistance. Among them, the role of sliding rheostat in this experiment is
A. change the resistance in the circuit and protect the resistance R.
B. change the current flowing through r and the voltage across it.
C. when changing the resistance r, adjust the sliding rheostat to keep the reading of the voltmeter unchanged.
D. when changing the resistance r, adjust the sliding rheostat to keep the ammeter reading unchanged.
14. Two conductors, A and B, pass through the same current, and it is found that the voltage across conductor A is higher than that across conductor B.. By comparing their resistance values, we can draw the following conclusions.
Libyan Arab Jamahiriya
C.r.a = r.b.d. It is impossible to compare who is older.
15. As shown in the figure below, when the sliders P 1 and P2 of two sliding rheostats slide to the right, the following statement is correct.
A.l 1 and L2 are dimmed, and B.l 1 and L2 are lightened.
C.l 1 lights up, and L2 lights up. D.l 1 lights up, and L2 lights up.
16. Some students mistakenly connected the ammeter in parallel at both ends of the lamp L 1 when doing the experiment of measuring current with ammeter. At this time, the observed phenomenon will be
A.both lights are off. B. the brightness of the two lamps remains unchanged.
C.L2 is brighter than before, and L 1 is not. D. it is impossible to judge.
17. In the circuit shown in the figure, the power supply voltage is 12 volts, the constant resistance R 1=7 ohms, and the maximum resistance of the sliding rheostat R0 is 5 ohms. When the switch S is closed, when the slider P of the sliding rheostat slides from the A end to the B end, the voltage representation changes as follows.
a . 5V ~ 12V b . 12V ~ 7V c . 0v ~ 5V d . 0v ~ 12V
18. There are two fixed-value resistors marked with the words "2A 10ω" and "15ω" respectively. If used in series in a circuit, the maximum current allowed to pass in the circuit is
A.1ab.2ac.3ad. Not sure.
19. In the circuit shown on the right, the power supply voltage is constant, and when the switch is closed, the lights L 1 and L2 can both emit light. Jordan L2
The filament suddenly burned out, and then
A. the reading of ammeter A 1 remains unchanged, while the reading of A2 becomes smaller.
B the reading of ammeter A 1 becomes smaller, while the reading of A2 remains unchanged.
C. the readings of ammeter A 1 and A2 decrease.
D. The readings of ammeter A 1 and A2 both increased.
20. As shown on the right, when the switch S is closed, what may happen is
A.l 1 and L2 both emit light. B.l 1 emits light, while L2 does not.
C. the power supply is damaged. The filament of L2 has been burnt out.
Two. Fill in the blanks (2 points for each blank, ***38 points)
2 1. The conductor resistance is determined by the material, length and ▲ of the conductor; Sliding rheostat is changed by changing the conductor.
Variable resistance; When the temperature is low enough, the resistance of the metal conductor will suddenly disappear, which is called ▲.
22. When the light bulb in the picture on the right is electrified, the light bulb can be lit. Please fill in the line below.
When switches K 1 and K2 are in the following states, bulbs A and B are turned on and off:
(1) K 1 on, K2 off ▲
(2) When K 1 is closed and K2 is disconnected ▲
(3) When K 1 and K2 are both closed ▲
23. When the voltage across the conductor is 6V and the current through the conductor is 0.2A, the resistance of the conductor is ▲Ω; If a voltage of 3V is applied across the conductor, the current passing through the conductor is ▲ A, and the resistance of the conductor is ▲ ω.
24. Xiaoli has electric lights, televisions, washing machines, refrigerators and other household appliances, all of which are connected to lighting circuits. If all household appliances are used at the same time, the total current on her circuit is ▲ (fill in "maximum", "constant" or "minimum", the same below), and the total resistance of the lighting circuit is ▲.
25. It is known that the resistance of a small light bulb is 20 Ω when it emits light normally, and the current passing through it is 1A, so the voltage at both ends of the small light bulb when it emits light is
▲ V. If the voltage of the power supply is 32 volts, in order to make the small light bulb emit light normally, a ▲ Ω resistor needs to be connected in series.
26. Resistors R 1 and R2 are connected in series and connected to a certain circuit. If u 1: U2 = 2: 3 and r 1 = 20ω, then R2 = ▲ If R 1 and R2 are connected in parallel at both ends of the original circuit, the ratio of the total series current to the total parallel current.
I chord: I parallel = ▲.
27. As shown in the circuit on the right, when the switch S is closed, the slider P of the sliding rheostat moves to the right.
In this process, the reading of ammeter will be brought, and the reading of voltmeter will also be brought.
28. Bend a resistance wire with uniform thickness and resistance value r = 27 into a circle, and ABC is the bisector.
If AB is connected to 5.4V power supply at two points, the current in the whole circuit is ▲ A. ..
Three. Experiment and analysis calculation (9 points for the 29th question, 6 points for the 30th question, 7 points for 3 1 question, 22 points for * * *).
29. The resistance value of resistor Rx is estimated to be between 6 ~10Ω. Xiao Ming uses the following components to measure the resistance value of Rx. The circuit diagram is shown in the left figure below, and the circuit connections are as follows. A wire is not connected properly.
(1) Please fill in the missing wires on the actual drawings.
(2) When connecting the circuit, the switch should be equipped with; Before closing the switch, the slider P should be placed at the ▲ end of the sliding rheostat. (Fill in "A" or "B")
(3) When the switch is closed, it is found that the ammeter has no indication and the voltage indication is close to 3V. The reason for the failure may be ▲.
(4) After troubleshooting, when measuring, two electrical indicators are shown in the following figure, so I = ▲, u = ▲.
According to the experimental data, rx = ▲.
(5) In the experiment, in order to reduce the error, what Xiao Ming needs to do is ▲.
(6) After the measurement, another student drew a diagram of the relationship between current and voltage of the resistance wire Rx, and found that the resistance value increased with the increase of voltage and current. After inspection, there is no problem with the circuit connection and meter reading. Please help him solve this problem: this is because ▲.
30. Research shows that the resistance of some metal resistors will change with the change of temperature. In physics, the properties of these metals can be used to make metal resistance thermometers, which can be used to measure very high temperatures. The principle is shown in the figure. In the figure, the measuring range of ammeter is 0 ~ 15 mA, the power supply voltage is constant at 3V, R' is a sliding rheostat, and the metal resistor is used as the temperature probe of the thermometer. When t≥0℃, the relationship between resistance value Rt and temperature T is Rt= 100+0.5t (ω).
What is the resistance measured by (1)Rt at 0℃? If the ammeter just reaches the full-scale current 15mA at this time, what is the resistance of the sliding rheostat r' connected to the circuit at this time?
(2) Keep the resistance of the sliding rheostat R' connected by the circuit in (1) unchanged, when
The temperature measuring probe Rt is placed at the temperature to be measured, and the ammeter reading is exactly 10mA.
What is the resistance of Rt at this time? What is the corresponding temperature?
3 1. As shown in the figure, it is the schematic circuit diagram of the anemometer designed by the eighth grade science extracurricular practice group in a middle school. Its power supply voltage U=3V, circuit protection resistance r1=10Ω, and resistance of uniform resistance wire R2 =10Ω.
The upper end of the wire (the resistance can be ignored) is fixed at the O point, and the lower end is tied with a piece of plastic.
A piece, when the wind blows the plastic piece from right to left, the metal wire swings to the left and touches the resistance wire.
Keep in good contact. The anemometer is modified from a voltmeter.
(l) When there is no wind, the plastic sheets are hung vertically. What is the voltage representation? In the circuit
What is the current?
(2) When the wind force is maximum, the metal wire slides to the leftmost end of the resistance wire. What's the reading of the voltmeter?
(3) Why not connect an ammeter in series in the circuit and refit it into an anemometer?
The third chapter of science in the second day of junior high school in Ningwai answers the class name of electricity test 2.
First, choose
1 2 3 4 5 6 7 8 9 10
1 1 12 13 14 15 16 17 18 19 20
fill (up) a vacancy
2 1.、 、
22.( 1)(2)(3)
23.ω、A、ω24。 、 、
25.v、ω26。 Ω、
27.、 28.A
Third, the experiment and analysis calculation
29.( 1)(2)
(3)
(4)、Rx=
(5)
(6)
30.
3 1.
The third chapter of science in the second day of junior high school in Ningwai answers the class name of electricity test 2.
First, choose
1 2 3 4 5 6 7 8 9 10
B C C A B A A C D D
1 1 12 13 14 15 16 17 18 19 20
B D C A C C B A A C
fill (up) a vacancy
2 1. Cross-sectional area, path length and superconductivity
22.( 1)A is on, B is off, (2)AB is off, and (3)AB is on.
23.30ω，0. 1A，30ω24。 Union, maximum and minimum.
25.20v, 12ω26.30ω, 6:25
27. Become smaller and bigger 28.0.9A
Third, the experiment and analysis calculation
29.(l) Slightly (2) Disconnected, A(3)R Disconnected, 0.3, 2.7, (4)9 (5) Measured (6) The change of conductor temperature for many times.
30.3 1.