"Measuring the Electric Power of Small Light Bulbs" Electric Power PPT

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"Measuring the Electric Power of Small Light Bulbs" Electric Power PPT

Part One: Guidance Design

Learning point 1: Principles of measuring electrical power

Question: To measure the electric power of the small light bulb shown in Figure 18-3-3, it is generally necessary to measure the ________ at both ends and the ________ passing through it, and then use the formula ____________ to calculate the electric power it consumes, which is A ________(optional "direct" or "indirect") measurement method.

Learning point 2: Measure the power of small light bulbs

Question 1: In order to measure the rated power of the small light bulb shown in Figure 18-3-4A, a student designed the circuit diagram shown in Figure B. Can he determine the wattage rating of the small light bulb? Why?

[Answer] No; because there is no way to ensure that the voltage across the small bulb is exactly 2.5 V.

Question 2: In order to measure the rated power of a small light bulb, the equipment required is ____________.

Question 3: After closing the switch, the next step is: _______________________________________________, read the ammeter indication, and then calculate the rated power of the small light bulb according to P=UI.

Measuring the electrical power of small light bulbs PPT, Part 2: Application examples

Type 1: Selection of experimental equipment

Example 1 In order to measure the electric power of a small light bulb marked with "8 V 0.4 A", Xiaohua designed the circuit as shown in Figure 18-3-3. The existing experimental equipment is as follows: Voltmeter V1 (range 0~ 3 V), voltmeter V2 (range 0 to 15 V), ammeter A1 (range 0 to 0.6 A), ammeter A2 (range 0 to 3 A), sliding rheostat R1 (“10 Ω　2 A”), sliding rheostat R2 ("50 Ω | 1 A"), a power supply (the voltage is always 12 V), a switch, and several wires.

To measure multiple sets of data safely and accurately, it is necessary to select appropriate experimental equipment, among which the voltmeter should be ________, the ammeter should be ________, and the sliding rheostat should be ________.

[Experimental Tips]In the "Measuring the Electric Power of Small Light Bulbs" experiment, you should pay attention to the following when selecting experimental equipment:

①Safety principle: The maximum measured value of the electric meter cannot be less than the maximum value of the measured circuit voltage and current, and the maximum current allowed to pass through the sliding rheostat should not be less than the maximum current of the circuit.

②Accuracy principle: Under the premise of ensuring safety, the selected meter range cannot be too large, otherwise the reading error will be large and the measurement results will be inaccurate.

③ Under the premise of ensuring safety, the maximum resistance value of the selected sliding rheostat cannot be too large, otherwise it will be difficult to adjust.

Type 2: Measuring the electrical power of small light bulbs

Example 2 [2017·Suzhou Excerpt] In a group experiment to measure the electric power of small light bulbs with a rated voltage of "2.5 V":

(1) Please use pen lines instead of wires to completely connect the physical circuit in Figure 18-3-4A.

(2) After Xiao Ming closed the switch, he found that the light bulb did not light up, the ammeter showed no reading, but the voltmeter showed a reading. The fault may be __________. After troubleshooting, move the slider to make the small bulb light normally. At this time, the current indicates the number as shown in Figure B, and the rated power of the small bulb is ________W.

(3) When Xiaohua was processing the experimental data, he calculated the average power of the small light bulbs (as shown in the table below). Do you think it is ______ (choose "reasonable" or "unreasonable") to process the data in this way? Reason: ____________________________.

[ Analysis into the circuit. (2) The bulb does not light up, the ammeter has no reading, but the voltmeter has a reading. The cause of the fault is that the bulb is broken. After troubleshooting, the current of the bulb when working at the rated voltage is 0.3 A, then the rated power of the bulb is P = UI =2.5 V×0.3 A=0.75 W. (3) The actual power of the light bulb is different under different voltages, so it is meaningless to calculate the average power.

[ Experimental Tips On the contrary; ② Do not connect the wrong ranges of the voltmeter and ammeter; ③ Do not cross the connections.

(2) Analysis of circuit failures and causes in the experiment of "voltammetric measurement of electric power of small light bulbs"

① The pointer of the ammeter or voltmeter deflects in the opposite direction → the positive and negative terminals of the ammeter or voltmeter are connected reversely.

② The voltage indication is the power supply voltage, and the ammeter has no indication → the small bulb is broken or the ammeter and voltmeter positions are interchanged.

③The current indication number is large and immutable, and the voltage indication number is the power supply voltage → Connect the two terminals on the sliding rheostat to the circuit (or the sliding rheostat is short-circuited).

④The current indication number is small and immutable, and the voltage indication number is small → Connect the two terminals below the sliding rheostat to the circuit.

⑤Both the voltmeter and the ammeter have no indication → there is an open circuit at a certain position in the series part except the small light bulb.

⑥The bulb is on before closing the switch, and the ammeter and voltmeter deflect normally. However, after closing the switch, the bulb goes out and the pointers of the two ammeters no longer deflect → the switch is at both ends of the power supply. At this time, the switch should be disconnected immediately and the error corrected to avoid Prevent the power supply from burning out.

⑦The moment the switch is closed, the bulb emits strong light and immediately goes out. The ammeter pointer deflects and then returns to the zero scale line, and the voltmeter still shows the reading. → Before closing the switch, the slider of the sliding rheostat is not moved to the position of maximum resistance and the power supply is turned off. The voltage is larger.

Measuring the electrical power of small light bulbs PPT, Part 3: Class Feedback

1. The basic instruments for measuring electrical power include ________ and ________. This method of measuring electrical power is called ________. The principle of measuring electrical power is ________. Please draw the experimental circuit diagram in the dotted box shown in Figure 3-1 A, and use strokes to replace wires, and connect the physical circuit in Figure B according to the circuit you drew.

2. In the experiment of "determining the electrical power of a small light bulb", the most reasonable division of labor between hands and eyes is ()

A． Move the slider of the rheostat by hand and observe the indication of the voltmeter with your eyes.

B． Move the slider of the rheostat with your hand and observe the ammeter indication with your eyes.

C. Move the slider of the rheostat by hand and observe whether the light bulb glows with your eyes.

D. Move the sliding piece of the rheostat by hand and observe the position of the sliding piece of the rheostat with your eyes.

3. In order to quickly and accurately measure the rated power of a small light bulb with a rated voltage of 2.5 V, at least ______ dry batteries are required. In order to improve the accuracy of the measurement, it is best to use the ______V range of the voltmeter. After closing the switch, adjust __________ so that the voltage indicates ________V. If the ammeter indicates 0.2 A at this time, the rated power of the small light bulb is ________W.

4. In the experiment of "determining the rated power of a small light bulb with a rated voltage of 3.8 V", Xiao Ming plans to use the following experimental steps. Please arrange them in a reasonable order for him: _______________________.

A． Close the switch B. Turn off the switch and connect the circuit according to the circuit diagram

C. Fill in the form with measurement data

D. Move the rheostat slider so that the voltage reading reads 3.8 V

E. Calculate the rated power of the small light bulb F. Read current indication number

G． Move the rheostat slider so that the resistance of the sliding rheostat in the circuit is maximized

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Update Time: 2024-06-26

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