"Electric Power" PPT courseware 7

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"Electric Power" PPT courseware 7

Xiao Ming discovered that when current passed through the electric fan in his home,

The work done in 10 s is 700 J,

When electricity passes through a television in your home

The work done in 10 s is 800 J,

Think about it: Which electrical appliance does the work faster when the current passes through it? Why

Demonstration experiment

Take a 40 W and an 800 W hair dryer respectively, connect them to the circuit, and compare the rotation speed of the aluminum plate of the energy meter.

The "40 W" on the light bulb and the "800 W" on the hair dryer indicate how quickly the power is consumed. The "800 W" light bulb consumes power faster than the "40 W" light bulb! In physics, electrical power is used to express the speed of consuming electrical energy!

1. Electric power (P)

1. Physical meaning: Indicates how fast the current does work.

2. Unit: watt, referred to as watt, symbol is W.

Common units: 1 kW = 103 W

1 W = 103 mW

3. Definition: If the work done by the current in such a long time as t is W, then the electric power P is

P=W/t

W——Joule (J)

t——second (s)

P——Watt (W)

And because W=UIt, then P =UI

Targeted practice questions

1. In daily life, the work done by the current passing through the electric fan in 10 seconds is 700 J. Can you calculate the power of the electric fan?

2. Based on the formula, determine whether the following is correct:

① The greater the power of an electrical appliance, the more electricity it consumes ( )

②The greater the power of the electrical appliance, the faster the energy consumption will be ( )

③Electrical power is a physical quantity that describes the amount of work done by an electric current ( )

④Kilowatt hour is the unit of electrical power ( )

⑤Electrical appliances that consume a lot of electricity must have greater power ( )

3. There is an electrical appliance in Xiao Ming’s home with a power of 40W. How much power does it consume after working for 1 hour?

(Can you do the calculation using two different units?)

4. Xiao Ming found that the voltage of an electrical appliance in his home is 220V and the power is 110W when it is working normally. Can you help Xiao Ming calculate the current of this electrical appliance when it is working normally based on these two conditions?

5. Xiao Ming found that the voltage of an electrical appliance in his home is 220V and the power is 110W when it is working normally. Can you help Xiao Ming directly calculate the resistance of this electrical appliance based on these two conditions?

2. The origin of “kilowatt-hour”

kW · h and kW are units of two different physical quantities.

P =W/t W = Pt

If the units of P and t are kW and h respectively, then after multiplying them, we get another unit of electrical energy: kilowatt-hour (degree).

1 kilowatt hour can be regarded as the electrical energy consumed by an electrical appliance with a power of 1 kW for 1 hour.

practice

1. The electrical power of a TV is 150 W and it is used for 3 hours a day. How many kilowatt-hours of electricity is used in a month? (Calculated based on 30 days)

Solution: P = 150 W = 0.15 kW

t=3h×30=90h

The electricity consumed in a month is

W = Pt = 0.15 kW × 90 h = 13.5 kW · h

Answer: The electricity consumption per month is 13.5 kW·h.

2. How long can 1 kilowatt hour of electricity power a 40 W light bulb?

Solution: t =W/P=1 kW·h/40 W =1 kW·h/0.04 kW=25 h

Answer: 1 kilowatt hour of electricity can power a 40 W light bulb for 25 hours.

3. Rated voltage and rated power

1. Rated voltage: The voltage at which an electrical appliance operates normally.

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

3. Actual voltage, actual power

The actual voltage applied across the electrical appliance.

The power of electrical appliances when operating at actual voltage.

U real = U amount, then P real = P amount; electrical appliances work normally.

U real > U amount, then P real > P amount; electrical appliances may be burned.

U real < U amount, then P real < P amount; electrical appliances cannot work normally.

Demonstration experiment

Take a light bulb labeled "2.5 V 0.5 W". Connect it to a 2.5 V circuit and it will light up normally. Connect them to 1.5 V and 3 V circuits respectively, observe and compare their brightness.

Phenomenon: When the voltage is 2.5 V, the bulb glows normally; when the voltage is lower than 2.5 V, the bulb glows dimly; when the voltage is higher than 3 V, the bulb glows strongly.

It shows that the electrical power consumed by an electrical appliance changes as the voltage across it changes.

practice

1. A colored light bulb with a rated voltage of 36 V needs to be connected in a 220 V circuit. How many of these light bulbs should be connected in series?

Solution: n =220 V/36 V≈ 6.1

Since the rated voltage cannot be exceeded, 7 such bulbs should be connected in series.

2. When a TV reporter talked about a factory that saved 5,000 kW·h of electricity in the first half of the year, he held up a hair dryer for haircuts and said: "My hair dryer is 500 watts, which is 0.5 kilowatts. This factory The electricity saved can run 10,000 of these hair dryers." Where did this reporter go wrong?

The reporter's statement confused the concepts of electrical energy and electrical power.

Keywords: Electric power teaching courseware, Lujiao edition ninth-grade physics PPT courseware download, ninth-grade physics slide courseware download, electric power PPT courseware download, .PPT format;

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Update Time: 2024-11-11

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