1. Put a solid ball into two containers containing enough water and enough alcohol. The force on the ball is 1.9 N and 1.8 N respectively, and the plot of alcohol is 1.8×113? kg/m3。

1. Analyze the floating and sinking state of the ball in water and alcohol

2. Find the density of the ball

Solution: Assuming that the ball does not float in water and alcohol, or floats or floats, there should be:

It is impossible because it conflicts with the known conditions of the topic;

If the ball sinks in both water and alcohol, there should be:

It is impossible because it contradicts the known conditions of the topic.

from the above analysis, it can be seen that when the ball is in water and alcohol, it can only float and sink.

because of this, the ball must float in water and sink in alcohol.

(2) Because the ball floats in the water,

∴ ①

According to the known condition: ②

Substitute ② into ①:

Figure 1

Second, put the cube block with a volume of 1.1×11-3m3 into a container filled with water as shown in Figure 1.

find: ① buoyancy of wood block;

② the gravity of the wood block;

③ The pressure at the bottom of the container increases after the wood block is put into the container

④ If the wood block is put into a liquid, the exposed liquid level is 4cm, and the density of the liquid is found.

solution: ① 5n; ②5N； ③125Pa； ④1.83×113kg/m3

Figure 2

Third, as shown in Figure 2, the power supply voltage is constant, the resistance of R1 is 11 ohms, the switch S is closed, the slider of the sliding rheostat slides to point B, the ratio of voltmeter to indicator is 5:7, and the sum of power consumed by R2 and R is four times that of R1. Find:

① Through R1 and R2. ②25 Euros; ③4:1

Figure 3

Electrical synthesis questions

6. (Ningbo City, 2117) A student used the circuit in Figure A to make the following research on the small light bulb with fuzzy rated voltage and rated power of 1w. After connecting the circuit as shown in Figure A, the switch S was closed, and the relationship between the current passing through the small light bulb and the voltage at both ends of the small light bulb was measured as shown in Figure B.

(1) According to the figure, the resistance of the small light bulb is (optional "constant" and "variable") during the experiment.

(2) when the voltage across the small bulb is 1.5V, what is the electric energy consumed by the small bulb within 2 minutes?

(3) What is the rated voltage of the light bulb?

7. (Yangzhou City, 2117) In the circuit of Figure A, the power supply voltage is 9V and remains unchanged, the specifications of ammeter are 1~1.4A, voltmeter is 1~15V, and the word "6V 6W" is marked on the bulb. The relationship between bulb current and voltage is shown in Figure B. Find:

(1) the current when the bulb normally emits light

.

8. (Chengdu, 2117) As shown in the figure, a light bulb L marked with "8V 4W" is connected in series with a sliding rheostat R, the switch S is closed, and when the slider P is at the B terminal, the voltmeter indicates 12V, and the light bulb normally emits light. When the slider slides from point B to point A, the resistance in the circuit increases by 6Ω. Find: (1) Resistance value and power supply voltage of the bulb; (2) What is the actual power of the bulb when the slider P is at point A?

(3) What approximation did you use in the calculation?

9. (Weihai City, 2117) As shown in the figure, the power supply voltage is constant at 24V, the small bulb is marked with the words "6V 3W", and the resistance of the constant resistor R2 is 24Ω. When the switch S is closed, S1 S2 is turned off and the slider moves to the midpoint of the sliding rheostat, the lamp L normally emits light

(1) What is the resistance of the bulb L?

(2) What is the maximum resistance of the sliding rheostat?

(3) When S1 S2 is closed, adjust the sliding rheostat to minimize the power consumed by the whole circuit.

What is the minimum value?

comprehensive questions of electrical mechanics

11. (Putian City, 2117) Xiaoqiang designed a tensiometer by using the physical knowledge he had learned. Figure A is its schematic diagram. The right end of the hard spring and the metal slider P are fixed together (the resistance of the spring is not counted, and the friction between P and R1 is not counted). The fixed resistance R1U=3V5Ω, and a b is a uniform resistance wire with a length of 5 cm, and its resistance value is 25Ω. The measuring range of ammeter is 1~1.6A, please answer:

(1) The purpose of connecting R1 in the circuit is.

(2) when the pull ring is not stressed, what is the reading of the ammeter between the slider and the A end after closing the switch S?

(3) It is known that the relationship between the elongation length △L of the spring and the tension force F is shown in Figure B. Through calculation, it is shown that when the switch S is closed, when the ammeter pointer is at 1.3A, what is the horizontal tension force acting on the pull ring?

11. (Huangshi City, 2117) As shown in the figure, it is a schematic diagram of an electronic scale designed by Xiaoxing by using the physical knowledge he has learned. The tray, the upper end of the spring and the metal slide P are fixed together, and the constant resistance R1=5Ω, ab is a uniform resistance wire with a length of 5cm, the resistance R=21Ω, the power supply voltage U=3V, and the range of the ammeter is 1~1.6A (excluding the resistance of the spring)

(2) It is known that the relationship between the compressed length △L of the spring and the pressure F is shown in the following table. After the switch S is closed, when the ammeter pointer is at 1.2a

, what is the mass of the object in the tray?

12. (Meizhou City, 2117) As shown in the figure, it is a schematic diagram of an electronic scale made by a research and study group. It uses the voltmeter as an indicator to indicate the mass of an object. The tray, the upper end of the spring and the slider of the sliding rheostat are fixed together, regardless of the mass of the tray and the spring. There are retractable wires between OA. When there is no object in the tray, the indicator of the voltmeter is 1. It is known that the resistance R1=5Ω, the maximum resistance of the sliding rheostat is 15Ω, the power supply voltage is U=3V, and the range of the voltmeter is 1~3V. Now, the object of 1kg is placed in the tray, and the slider is just 1/3 away from the upper end of R (excluding friction, the spring is always within the elastic limit). Please calculate the answer:

(1) What is the indication of the voltmeter when the object of 1 kg is placed in the tray?

(2) what is the maximum mass that can be measured by this electronic scale? How many volts should this mass be marked on the voltmeter?

13. (Lishui City, 2117) Xiaowen designed a pallet scale for measuring the gravity of an object, as shown in the schematic diagram, in which the pallet is used to place the object to be measured, OBA is a lever that can rotate around 1: 11, R1 is a pressure sensor, (its resistance value will change with the pressure, and the relationship is shown in the following table), and R1 is a fixed resistance. In order to display the gravity (essentially a voltmeter with a range of 1~3V), it is known that OA∶OB=2∶1, R1=111Ω, and the power supply voltage is constant at 3V (ignoring the gravity of the tray, lever and pressure bar)

(1) When there is no object on the tray, the resistance value of the pressure sensor R1 is

(2) When the measured object is placed on the tray.

(3) What is the gravity of the measured object in question (2)?

14 (Nanjing, 2117) A research study group designed a device for measuring wind power. Its principle is as shown in the figure. The windward plate is connected with one end of a light spring and passes through a smooth metal rod. The spring is made of insulating material, and the resistance of the uniform metal rod changes uniformly with the length. When working, the windward plate always faces the direction in which the wind blows. In the circuit, the left lead is connected to the M end of the metal rod, and the right lead is connected to the N point on the windward plate and can slide on the metal rod with the windward plate. The leads at both ends are in good contact with the metal rod. It is known that the power supply voltage is always 4.5V, and the planting resistance R=1.1Ω. The relationship between Rx in the circuit connected with the metal pole and the wind force F borne by the windward plate is shown in Figure B. < P > If a voltmeter is connected in the circuit, the voltage indicator will increase with the increase of the wind force, please draw the voltmeter in a proper position.

when there is no wind, find the indication of voltmeter and the electric power consumed by fixed resistance r;

If the voltmeter has a range of 1~3V, find the maximum wind power that can be measured by the device

Comprehensive problem of electricity and heat

15. (Guiyang City, 2117) In an extracurricular activity, Xiaoyue made relevant observation and research on electromagnetic furnace, and recorded the relevant data of the induction cooker and her electric energy meter, as shown in the following table: According to the relevant information obtained by Xiaoyue during the activity, Seek to record the research activities of the observed object during this period

Nameplate of the induction cooker U amount =221V P amount = 1 kW ① Heat a pot of water with the induction cooker (the mass of water is 2kg, and the initial temperature is 31℃.② Turn off other household appliances, only connect the induction cooker to the circuit to boil water, and observe that the dial of the electric energy meter turns 151r within 5 minutes. At this time, the temperature of water measured by thermometer is 51℃

nameplate of electric energy meter is 221v11 (41) a

51hz 2111r/kwh

(1) heat absorbed by water (2) actual power of induction cooker (3) efficiency of boiling water by induction cooker

16. (Weihai City, 2117) Newly bought by Xiaogang's classmate. Part of the data on the nameplate is shown in the following table

(1) What is the current and resistance of the water heater during normal operation?

Model PCD-H41II

Volume 41L

Rated maximum temperature 75℃

Rated voltage 221 V

Rated power 1.1 kW

Rated internal pressure 1.75 MPa

(2) If What is the heating efficiency of the water heater during this time? (regardless of the change of resistance with temperature)

functional steam ironing with rated voltage of 221V

steam dripping with rated frequency of 51HZ

rated power of 1111W, mass of 1.3kg

bottom plate area of 161cm2, self-standing

17. (Zhenjiang City, 2117) As shown in the figure, it is a physical diagram and nameplate of a household steam electric iron. When in use, the water drops in the water tank drop into the heated steam chamber of the soleplate, and rapidly vaporize to generate downward steam

(1) Inject 1.3kg of water into the iron water tank,

lay it flat on a horizontal desktop, and

find the pressure of the iron on clothes

(2) preheat it before steaming with the iron, so that the temperature of the metal soleplate can be raised from 21℃ to 221

.

(3) During steam ironing, water drops into the steam room, and heat is taken away due to water heating and vaporization. When the temperature of the metal soleplate drops to 191℃, the temperature control switch is automatically closed, and the electric iron works normally. When it is heated to 221℃, the temperature control switch is automatically turned off to stop heating, and so on. If the working condition of the steam electric iron changes as shown in the figure, it will iron a piece of clothing for 12min.

18. (Suifang City, 2117) Xiaoxing designed an automatic control device for her own bath electric water heater. As shown in the figure, R1 is a thermistor (placed in the water heater), and the relationship between its resistance and temperature is shown in Table 1. Table 2 is the nameplate of this electric water heater. It is known that the resistance R2 of relay coil is 11Ω, and the voltage U1 of the left power supply is 6V. When the current in the relay coil R2 increases to a certain value, the armature of the relay is sucked down, and the circuit of the electric water heater is closed. Please answer

What is the resistance of the electric water heater during normal operation?

analyzing table 1, how does the resistance of thermistor change with temperature?

if the temperature in the electric water heater is controlled between 31℃ and 61℃, what is the working current of the relay coil when the armature is sucked down and the electric water heater circuit is disconnected?

when the electric water heater works normally, how long does it take to heat the whole tank of water from 31℃ to 61℃? (excluding heat loss)

19. (Linxi City, 2117) The data of Huayang 1871 series solar water heater are as follows:

Vacuum tube diameter (mm) 71×1811 specification (branch pipe) 15

Overall dimension (mm mm) 1841×1597×1765 insulation layer (mm) 61. If

the time of receiving solar energy every day is counted as 8 hours

, and the water heater can convert 51% of the received solar energy into the internal energy of water, how many degrees Celsius can the water heater heat a box of water with an initial temperature of 21℃ in a normal day?

(2) If an electric water heater marked "221V 1511W" is used to work at the rated voltage, how long will it take to raise the same temperature of the same tank of water?

(3) if the electricity price is 1.54 yuan /KWh, how much electricity can be saved every month (according to 31 days)?

21. (Xiamen City, 2117) There is an automatic electric heating bottle in the office. The diagram and table show its principle and parameters.

a is an automatic temperature control switch, which automatically disconnects the circuit when the water temperature reaches the set temperature;

when the temperature is lower than the set temperature, the circuit is automatically turned on. It is known that the specific heat capacity of water is

4.2× 113 j/(kg℃). Please make the following calculations through analysis:

(1) 91% of the heat released by the electric thermos is absorbed by the water. How long should the electric thermos work normally when boiling a bottle of water at

21℃ (standard atmospheric pressure)?

(2) when the yellow light is on, is the electric thermos in the heat preservation state or the heating state? What is the resistance of thermal insulation element

r when it works? (Note: the power consumed by the indicator lamp can be ignored, and the heat preservation work

rate refers to the power consumed by the whole circuit)

Model P2155-B

Power supply AD221V 51Hz

Heating power 811W <