"Measuring the Electric Power of Small Light Bulbs" Electric Power PPT Courseware 6

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"Measuring the Electric Power of Small Light Bulbs" Electric Power PPT Courseware 6

Rated voltage, rated power

1. Rated voltage Ue is the voltage at which the electrical appliance works normally.

2. Rated power Pe is the power of the electrical appliance when it is working normally (power at rated voltage).

Tip: "Working" is "rated"

Actual voltage, actual power

1. The actual voltage Us is the voltage when the electrical appliance is actually working.

2. Actual power Ps is the power of the electrical appliance when it is working normally (power under actual voltage).

Remember: what voltage corresponds to what power

Measurement of electrical power

Recall the three derivation formulas for electrical power:

①P=UI ②P=I2R ③P=U²/R

Please think about which formula is best to use to measure the electrical power of a light bulb?

①P=UI

Precautions:

1. When connecting a circuit, the switch should _________.

2. Before closing the switch, the sliding rheostat should be scribed _________, and the principle of _________ should be followed when connecting the sliding rheostat.

3. When connecting the positive and negative terminals of the ammeter and voltmeter, pay attention to ________, estimate the current and voltage in the circuit, and select the ________ range. If it cannot be estimated, use the switch to select _________ for _________.

Experimental steps:

1. Turn off the switch, connect the circuit according to the circuit diagram, and adjust the sliding blade of the sliding rheostat to the maximum resistance value.

2. Close the switch, adjust the voltage to the normal working voltage of the small bulb (2.5V) through the sliding rheostat, record the U and I values, and observe the brightness of the bulb.

3. Make the voltage at both ends of the small bulb approximately 1.2 times the rated voltage, observe the brightness of the small bulb, record the U and I values, and observe the brightness of the bulb.

4. Make the voltage at both ends of the small bulb lower than the rated voltage, record the U and I values, and observe the brightness of the bulb.

Consolidate and sublimate

1. As shown in the figure is an experimental circuit diagram for measuring the resistance and electric power of a small light bulb. When the slider of the sliding rheostat moves to the left, the changes in the indications of the ammeter and voltmeter are ()

A. increase, enlarge

B． increase, decrease

C. decrease, increase

D. reduce, reduce

2. In the experiment of "determining the rated power of a small light bulb": the circuit is shown in Figure 7-19 on page 22. The rated voltage of the small light bulb is 2.5V, the resistance is about 10Ω, and the power supply is two dry cells.

(1) Please use pen lines instead of wires to connect the components in Figure 7-20A to form a circuit that meets the requirements of this experiment (the connections cannot cross).

(2) After connecting the circuit correctly, close the switch S and find that the lamp L does not light up. The cause of the failure may be ( )

A. There is an open circuit at the ammeter B. There is an open circuit at the positive and negative terminals of the voltmeter

C. Small bulb L is short-circuited D. The filament of small bulb L is broken

(3) After troubleshooting, when the small light bulb L lights up normally, the ammeter pointer position is as shown in Figure 7-20B, then the rated power of the small light bulb L is ______W.

Analyze the causes of the following experimental phenomena

Phenomenon 1: Xiao Ming connected the experimental circuit, closed the switch, and found that the pointer of the voltmeter was reverse biased.

Analysis: The "+" and "-" terminals of the voltmeter are connected reversely.

Phenomenon 2: Xiaoqiang connected the experimental circuit, closed the switch, and moved the slider. The brightness of the bulb changed significantly, but the pointer of the ammeter swing was small, making it difficult to read the current value.

Analysis: The range of the ammeter selected is too large. The current of small light bulbs is generally less than 0.6A, so the range of 0~0.6A can be used.

Phenomenon 3: In the experimental circuit that Xiaoyang connected, the rheostat and the light bulb were connected in series, but when the switch was closed, the small light bulb was found to be particularly bright.

Analysis: 1. The sliding rheostat was not adjusted to the maximum resistance before closing the switch.

2. This situation will also occur if the upper two terminals of the sliding rheostat are connected to the circuit at the same time.

Phenomenon 4: Xiaoyu connected the circuit. After closing the switch, he found that the small bulb did not light up, the voltmeter showed a reading (close to the power supply voltage), and the ammeter pointer did not move.

Analysis: There may be two reasons for this phenomenon:

One is that the small bulb is broken, that is, the filament of the small bulb is broken or the wiring is not connected properly.

Another reason is that the ammeter and voltmeter are connected reversely.

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Update Time: 2024-09-08

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