"Current Work" Current Work and Electric Power PPT Courseware

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"Current Work" Current Work and Electric Power PPT Courseware

Electric power

(1) Concept: The work done by electric current is called ______.

(2) Essence: The process of current doing work is the process of converting electrical energy into ______.

(3) Conversion of electric energy: In the home, electric heaters convert electric energy into ______ energy; washing machines convert electric energy into ______ energy; charging batteries convert electric energy into ______ energy; fluorescent lamps convert electric energy into ______ energy _____can wait.

(4) The unit of electrical power: The international unit of electrical power and electrical energy is ______, and the symbol is ______. In daily life, ______ is commonly used as the unit of electrical energy, and its symbol is ______. 1kW•h=______J.

(5) Measurement of electrical power: Electrical power is usually measured by ______.

(6) The work done by the current on a certain circuit is proportional to the voltage at both ends of the circuit, the current in the circuit and the power-on time. The formula for calculating electrical power:______.

Explore what factors are related to the amount of work done by electric current

(1) The conversion method displays the amount of work done by the current: all the work done by the current passing through the conductor is converted into the internal energy of the kerosene. "The amount of work done" is judged and displayed by "the difference in the temperature of the kerosene".

(2) Control variables: ① Connect two resistors with different resistances in series (when the current is the same), and explore the relationship between the amount of work done by the current and the voltage. ② Connect two resistors with different resistances in parallel (when the voltage is the same) and explore the relationship between the amount of work done by the current and the size of the current. ③In the above experiment (when U and I are the same), the longer the energization time is, the more heat is generated by the conductor. This shows that the amount of work done by the current is also related to the energization time.

(3) Conclusion: The formula of electric power is W=UIt. The units of each physical quantity are J, V, A, and s respectively.

[Example question] Regarding the question "What factors are related to the work done by electric current?", Liu Xing made the following conjecture:

Conjecture A: The work done by current may be related to voltage;

Conjecture B: The work done by the current may be related to the current;

Conjecture C: The work done by the current may be related to the power-on time.

In order to verify his conjecture, he chose the device shown in Figure A (except for the different resistance values ​​of the resistance wires, the other conditions are the same) and a power supply, switch, voltmeter, and several wires. He connected two resistance wires in series and connected them to the circuit, as shown in Figure B.

(1) The purpose of connecting two resistance wires in series to the circuit is to control the ________ passing through the resistance wire and the energization time to be the same. The scientific inquiry method he used is ________.

(2) Before turning on the circuit, he thought: After powering on for a period of time, observe the changes in the thermometer readings. If the changes in the two thermometer readings are different, it means that the work done by the current is related to the _________ at both ends of the resistance wire, which verifies the conjecture_ _______.

Tip: When a physical quantity is related to multiple factors, pay attention to the control variables during the exploration process.

Analysis: Since it is conjectured that the work done by the current is related to multiple factors, the controlled variable method must be used when designing the experiment; when connected in series, the currents everywhere in the circuit are equal. It can be seen that the purpose of connecting the resistance wires in series is to control the current and the energization time to be the same. Since the two resistance wires The resistances are different, so the voltages at both ends are different. If the thermometer displays different numbers, it means that the work done by the current is related to the voltage.

Knowledge point 1 Electric energy meter

1. Zhang Ying’s electric energy meter indicates at the beginning of the month and at the end of the month. If the local electricity bill price is 0.5 yuan/(kW·h), her family’s electricity bill this month will be _________ yuan.

2. The electric energy meter of Xiao Ming’s home reads 7 846.6 kW·h at the beginning of the month. The reading at the end of the month is as shown in the figure. If the electricity bill for 1 kilowatt hour is calculated as 0.49 yuan, then the electricity bill for Xiao Ming’s home this month is ________ Yuan.

3. There is a parameter "3 000 Revs/(kW·h)" on the electric energy meter. Its meaning is: for every 1 kilowatt-hour of electric energy consumed by the electrical appliance connected to this electric energy meter, the turntable on the electric energy meter will Just turn ________. 1 kilowatt hour is equal to ________ joules.

Knowledge point 2 Electric power

4. Regarding electric power, which of the following statements is correct ()

A. The conversion of electrical energy into kinetic energy is called electrical work

B. The electric energy meter is an instrument that measures the amount of electrical energy consumed. It cannot measure electrical power.

C.Kilowatt hour is not a unit of electrical power

D. Joule is the unit of electrical power

Knowledge point 3: What factors are related to the work done by electric current?

5. Li Ming used the device as shown in the figure to explore what factors are related to the heat generated by current. He filled two identical flasks with kerosene, placed a resistance wire in each bottle, and R A was greater than R B. After energizing for a period of time, the kerosene in the glass tube of bottle A rose higher than that of B. This phenomenon can explain that the heat generated by current is related to which of the following factors ()

A.Voltage B.Current C.Resistance D.Power-on time

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Update Time: 2024-07-07

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