"Electric Energy and Electric Power" Electric Energy and Electric Power PPT Courseware 3

"Electric Energy and Electric Power" Electric Energy and Electric Power PPT Courseware 3

learning target:

1. Understand the concept and units of electrical power.

2. Explore what factors are related to the size of electrical power

3. Understand the calculation formula of work and be able to apply it to perform simple calculations.

4. Understand the reading and use of electric energy meters

1. Electric power

1. Definition: The work done by electric current. Represented by W

The process of current doing work is the process of converting electrical energy into other forms of energy.

2. Unit:

Joule, referred to as "joule", symbol: J

1kW·h=3.6×106J

2. What factors are related to electrical power?

①The relationship between electric power and voltage

Conclusion: Under the same conditions of ___ and ______, the greater the _____, the more work the current will do.

②The relationship between electrical power and current

Conclusion: When ___ and ______ are the same, the greater the ____, the more work the current does.

③The relationship between electric power and power-on time

Conclusion: When ___ and ___ are the same, the longer the _______, the more work the current does.

Summary: What factors are related to electrical power?

Electrical power is related to voltage, current and power-on time

The bigger the ____, the bigger the ____, and the longer the ____, the more work the current does.

3. Electric energy meter (also known as watt-hour meter)

Function: Measure the electrical energy consumed by electrical appliances within a period of time

Read textbook P19 and solve the following questions within two minutes:

1. 220V means __________

2. 10 (20) A means ____________________

3. 1250r/kwh means ____________________

4. The reading of the electric energy meter at the end of January __________

The reading on the electric energy meter at the end of February __________

Shared electricity________kwh in February (charged as an integer)

Calculated at 0.5 yuan per kilowatt hour, the electricity bill in February is _____

The reading of Xiaohua’s electric energy meter at the beginning of a certain month is shown in Figure A below, and the reading at the end of the month is shown in Figure B. So how many kilowatt-hours of electricity does Xiaohua’s house consume each month? Approximately how many joules? If the local electricity bill is 0.5 yuan/KW·h, how much electricity bill should Xiaohua’s family pay that month?

Solution: ①W=W base-W initial=1352.9-1268.4 =84.5 (degree)

②W = 84.5×3.6×106J =3.042×108 J

③84.5 KW·h×0.5 yuan/KW·h=42.25 yuan

Example 1: A soldering iron is connected to a 220V circuit, and the current flowing through it is 350mA. How much power does it consume when it is powered for 30 minutes?

Known: U=220V, I=350mA=0.35A, t=1800s.

Asking for: W=?

Solution: From the formula of electric power, we get

W=UIt

=220V×0.35A×1800s

=1.386×105J.

Answer: After energizing for 30 minutes, the electric furnace iron consumes 1.386×105J of electric energy.

Example 2: The dial of an electric energy meter is marked "1200r/(kW·h)", and a certain electrical appliance is connected to the meter alone. After the electrical appliance works for 4 minutes, the electric energy meter turntable rotates 55r. If the rated voltage of the electrical appliance is 220V, find the current through this electrical appliance

Solution: The energy meter turntable rotates 55r within 4 minutes, which means that the power consumed by the electrical appliance is:

W =55r/1200r/(kW·h)=55/1200kW·h

=55/1200×3.6×106J=1.65×105J

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