"Electric Power" Electric Power PPT Teaching Courseware (Lesson 2)

"Electric Power" Electric Power PPT Teaching Courseware (Lesson 2)

Part One: Knowledge Management

1. Rated power and actual power

Rated voltage: The voltage of the electrical appliance when it is working normally.

Rated power: The electrical power of an electrical appliance when working at rated voltage.

Actual power: The electrical power of electrical appliances when working at actual voltage.

Relationship: (1) When U real = U amount, then P real = P amount, the electrical appliance works normally;

(2) When U real < U amount, then P real < P amount, the electrical appliance cannot work normally;

(3) When U real > U amount, then P real > P amount, which may damage electrical appliances.

Note: (1) The brightness of the bulb depends on the actual electrical power.

(2) For a certain electrical appliance, the rated power has only one value, but the actual power can have countless values. When the resistance is constant, the actual voltage is n times the rated voltage, and the actual power is n2 times the rated power, that is, P real P amount = U real U amount 2 = n2.

2. Measurement of electrical power

Measurement method: (1) Use a voltmeter to measure the voltage at both ends of the electrical appliance, use an ammeter to measure the current passing through the electrical appliance, and calculate the electrical power of the electrical appliance through the formula P=UI.

(2) The power of electrical appliances can also be measured with an energy meter and stopwatch.

Electric power PPT, part 2: classification and exploration

One type: rated power and actual power

[2019•Shenyang, Liaoning]Three electric lamps with specifications of "220 V | 40 W", "36 V | 40 W" and "110 V | 40 W", each working at the rated voltage, their lighting conditions for ( D )

A． "220 V 40 W" lamp is the brightest

B． "36 V 40 W" lamp is the brightest

C. "110 V 40 W" lamp is the brightest

D. Three electric lights are equally bright

[Analysis] It can be seen from the question that the rated power of the three electric lamps is the same. When the three electric lamps work at their respective rated voltages, the actual power of the three electric lamps is equal to their respective rated power, so the actual power of the three electric lamps is the same. , both are 40 W, and the brightness of the lamp is determined by the actual power, so the brightness of the three lamps is the same.

[Method Summary] To answer this kind of problem, you only need to grasp that the brightness of the light bulb is determined by the actual power of the light bulb.

Type 2: Power of electrical appliances

[2018•Hohhot, Inner Mongolia]The picture below shows the circuit working principle diagram of a certain electric heater. There is a main control switch S1, a temperature control switch S2, and two heating resistance wires R1 and R2 (both resistance values ​​remain unchanged). The heater has a rated voltage of 220 V, a heating power of 4840 W, and a heat preservation power of 400 W. beg:

(1) When S1 and S2 are both closed, the heater is in the heating (optional "heating" or "keep warm") state. What is the total current in the circuit at this time?

(2) During the peak power consumption period in the evening, if the actual voltage is only 200 V, the actual power of the heater in the heat preservation state. (keep integers)

[Method Summary] The key to answering this type of question is to flexibly use the characteristics of parallel circuits and the electric power formula, pay attention to the size of the resistance in the circuit when the switch is closed, and collect useful information.

Electric power PPT, the third part: in-person evaluation

1. [2019•Beijing Chaoyang District]When the following household appliances are working normally, the rated power is about 800 W (C)

A． Energy-saving lamps b. TV set

C. Rice cooker D. laptop

2. [2019•Jilin Baicheng]When two electric lamps marked with "220 V 40 W" and "36 V 40 W" can emit light normally, their luminous condition is (C)

A． "220 V | 40 W" lamps are brighter

B． "36 V 40 W" lamp is brighter

C. Both lights are equally bright

D. Unable to judge

3. A lamp is marked with "220 V 100 W". If it is connected to both ends of the 110 V power supply, assuming that the resistance of the lamp remains unchanged, the correct statement below is (C)

A． Its power rating becomes half the original

B． The magnitude of the current passing through it remains unchanged

C. Its actual power becomes 1/4 of the original

D. Its actual power becomes 1/2 of the original

4. [2018•Hunan Xiangxi Prefecture]There are two kinds of light bulbs, 40 W and 20 W, installed in the communication room of a school. When they turned on the lights at night, the students found that the 40 W light bulb was brighter than the 20 W light bulb. This means that the 40 W light bulb was brighter than the 20 W light bulb. The actual power of the bulb is greater than that of the 20 W bulb (optional "larger" or "smaller").

5. [2018•Shandong Dezhou]Before going out at 8:00 in the morning, Xiaogang checked the electric energy indicator of his home as shown in Figure A, and then turned off other electrical appliances in the home and only allowed the refrigerator to work. After returning home at 18:00 in the afternoon, I checked the energy meter again. The number displayed is as shown in Figure B. Then the electricity consumed by Xiaogang’s refrigerator during this period is

0.5 kW·h, the actual electrical power of the refrigerator is 50 W.

Electric power PPT, part 4: layered operations

1. [2019•Jilin Changchun]A lamp marked with "36 V 40 W" is connected to a circuit. The current passing through the lamp is 1 A. Assuming that the resistance of the lamp does not change with temperature, then this lamp The actual power of the lamp is (C)

A． Equal to 40 W B. equal to 36 W

C. Equal to 32.4 W D． None of the above statements are correct

2. [2018•Neijiang, Sichuan] Connect the small light bulb L1 with the specification "2.5 V·0.3 A" and the small light bulb L2 with the specification "3.8 V·0.3 A" in series and connect them to the 3 V power supply. The following judgments are made The correct one is (B)

A． The resistance of L1 is greater than the resistance of L2

B． The brightness of L1 is smaller than the brightness of L2

C. Both bulbs glow normally

D. The actual power of the two light bulbs is equal

3. [2019•Quanzhou, Fujian]When an electric kettle marked "220 V | 800 W" works normally, it can boil a pot of water in 8 minutes. When it is connected to a 110 V power supply, the time it takes to boil the same pot of water is (not considering energy loss) (D)

A． 4 minutes b． 8 minutes

C. 16 minutes D. 32 minutes

4. [2018• Chengdu, Sichuan The actual power of the light bulb is less than (optional "greater than", "less than" or "equal to") 60 W.

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For more information about the PPT courseware "Understanding of Electric Power Rated Power and Real Power and Using Rating to Find Practical Problems", please click on the ppt tag "Understanding Electric Power Rated Power and Real Power Using Rating to Find Practical Problems" ppt tag.

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