"Measuring Electric Power" Current Work and Electric Power PPT Courseware 2

Description

"Measuring Electric Power" Current Work and Electric Power PPT Courseware 2

Warm review:

1. What is electrical power?

The work done by the current per unit time

2. What is the physical meaning of electrical power?

Electric power is a physical quantity that expresses how quickly an electric current does work.

3.What are the methods for calculating electric power?

Electric power calculation formula

P=w/t

P=UI

P=U²/R

P=I²R

Learning goal: Master how to measure small light bulbs

Key points: Be able to measure the power of small light bulbs, and be able to distinguish between actual power and rated power.

Difficulty: Design a circuit to measure the power of small light bulbs and troubleshoot various faults

220V: represents the rated voltage, which is the voltage at which the small light bulb can work normally.

50W: represents the normal working power of the small light bulb

The light bulbs we use in our daily life are marked with such parameters, which tell us its rated voltage and rated power. Without the above parameters, it would be very inconvenient for us to use them.

Measure the electrical power of a light bulb

Now I give you a small light bulb. On the nameplate there is only ________ but no ________. Can you measure the rated electric power of the small light bulb based on the knowledge we have learned before? How to measure it?

According to the formula: P=UI

Experiment purpose: measure the electrical power of small light bulbs

Experimental principle: P=UI

Experimental equipment: power supply (4.5V), switch, wire, small light bulb (2.5V 0.3A)

Connection circuit:

Note: The switch should _________ when connecting the circuit.

The sliding rheostat should be in _________.

Note: Adjust the sliding rheostat carefully to avoid excessive actual voltage and burning out the bulb.

Record the readings of the voltmeter and ammeter in time and fill in the experimental form.

Measurement requirements

Measure the actual power in the following three situations respectively.

(1) Make the small bulb glow normally at the rated voltage of 2.5V.

(2) Make the voltage across the small bulb 1.2 times the rated voltage (3V), and observe the brightness of the small bulb.

(3) Make the voltage across the small bulb lower than the rated voltage and observe the brightness of the small bulb.

Analysis and Demonstration

The actual electrical power consumed by small electric lamps is not necessarily equal to the rated power. The actual power of the small light bulb when it is normally emitting light is equal to the ______ power of the small light bulb.

U real=U amount, P real____P amount

U real>U amount, P real____P amount

U real

Under different voltages, the actual power of the small bulb ____. The greater the actual voltage, the actual power of the small bulb ____.

The brightness of the light bulb depends on the ____ power. The greater the ____ power, the smaller the light bulb is.

Experimental evaluation

Students, after studying this lesson, reflect on what aspects of the experiment may make mistakes and where large errors are prone to occur? What problems did you discover during the design, operation, and analysis processes?

What did you learn? Which ones are not mastered well?

Practice in class:

As shown in the figure is a circuit diagram for measuring the rated power of a light bulb with a rated voltage of 2.5V.

①a is _____ table, b is _____ table

② Connect the equipment according to the diagram. Before measurement, the switch should be _____ and the slide P should slide to the _____ point.

③If the resistance of the light bulb is 10Ω, the power supply consists of two dry batteries connected in series, the ammeter has two ranges: 0-0.6A and 0-3A, and the voltmeter has two ranges: 0-3V and 0-15V, then the range of meter a should be Select the _____ file, and the b meter range should select the _____ file.

④ Close the switch and find that the voltage at both ends of the small bulb is only 1.8V. The sliding plate P of the sliding rheostat should move to the _____ end so that the voltage can be expressed as _____V. At this time, the actual power of the bulb is the rated power.

Summary of this lesson

Uactual=U amount, Pactual___P amount

U real>U amount, P real___P amount

U real

Under different voltages, the actual power of the small bulb is different. The greater the actual voltage, the greater the actual power of the small bulb.

After-class exploration and reflection

Just now we used a voltmeter and ammeter to measure the power of a small light bulb. This is a method commonly used in experiments. In real life, we can also use an electric energy meter to measure the power of electrical appliances. Can you tell the truth?

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