Beijing Normal University Ninth Grade Physics Volume 2

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"Electric Power" Electric Power and Electric Power PPT Courseware 6

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Physical meaning means ______ that consumes electrical energy

Definition: The ratio of the work done by the current to the time taken to complete the work is called electrical power.

Formula The power of an electrical appliance is equal to its ____________. Definition formula P=W/T, basic formula______

Unit International unit: watt, referred to as watt, symbol is W

Rated voltage

rated power

The voltage when the electrical appliance is ________ and the power of the electrical appliance at ________. The rated voltage and rated power of an electrical appliance are determined, and there is only one

actual power

The power of an electrical appliance when _________ is uncertain and changes with changes in the working conditions of the electrical appliance.

1. Electrical work and electrical power

(1) The physical concepts described by electric work and electric power are different: Electric work is a physical quantity that describes how much work a current does, while electric power is a physical quantity that describes how quickly a current does work. Electrical power is not only related to the amount of work done by the current, but also related to the time of doing the work.

(2) The calculation formulas of electric work and electric power are different: the basic calculation formula of electric work is W=UIt. It can be seen that the amount of work done by the current is related to the three factors of voltage, current and power-on time, and is determined by the three factors of them. The product is used to determine the size. The basic formula of electric power is P=UI, which shows that electric power is related to two factors: voltage and current, and its size is determined by their product.

(3) The units of electric work and electric power are different: the units of electric work are J and kW·h, while the units of electric power are W and kW.

(4) Electric work and electric power are closely related. Using the formula P=W/T, we can get W=Pt

[Example 1] Which of the following statements about electric power and electric power is correct ()

A. The more work the current does, the greater the electrical power.

B. The greater the electric power, the faster the current does work.

C. The shorter the time the current does work, the greater the electrical power.

D. When current does the same work, the longer it takes, the greater the electric power is.

Analysis: The common mistake students make in this question is to only determine the amount of electrical power by one factor and mistakenly choose items A and C. When comparing the magnitude of electric power, we must consider two aspects: work and time. We cannot mechanically separate work and time to consider electric power. Electrical power indicates how fast the current does work, not how much work the current does. It can be seen from the formula P=UI: within a certain period of time, the more work the current does, the greater the electrical power; the longer it takes to do the same work, the smaller the electrical power. Option A does not specify the time of work; Option C does not specify the amount of work; Option D reverses the conclusion; only Option B is correct.

2. Rated power and actual power

The normal operating voltage marked on the electrical appliance is called the rated voltage, represented by the U amount; the power marked at the rated voltage is called the rated power, represented by the P amount. The rated voltage and rated power of an electrical appliance are determined, and there is only one. The actual voltage is the voltage of the electrical appliance when it is actually working, and is often represented by U real; the power of the electrical appliance at the actual voltage is the actual power, which is often expressed by P real. The actual power is the power of the electrical appliance when it is actually working. It is uncertain and changes with the changes in the working conditions of the electrical appliance. If the actual voltage is not equal to the rated voltage, the actual power is not equal to the rated power.

[Example 2] In the circuit shown in the figure, the power supply voltage remains unchanged and R is a fixed-value resistor. When the switch is closed, the small light bulb L marked "8V 8W" just lights up normally; if the fixed-value resistor R does not Change, replace L with another small light bulb marked "8 V 4 W", after closing the switch, the actual power consumed by the small light bulb when working ()

A. Greater than 4 W B. Equal to 4 W

C. Less than 4 W D. Unable to determine

Analysis: According to the formula R=U²/P, when the voltage is the same, the greater the electric power, the smaller the resistance, so the resistance of the "8V 8W" light bulb is smaller than that of the "8V 4W" light bulb; according to the voltage dividing characteristics of the series circuit resistors It can be seen that after the change, the voltage across the bulb becomes larger and is greater than 8 V, so the power consumed by this bulb is greater than 4 W. So the correct option is A.

1. The electric power of a small or medium-sized flashlight bulb is about 1 W, which means ()

A. The small light bulb consumes 1 W of electricity in 1 s.

B. The electric power consumed by the small light bulb in 1 s is 1 J

C. The electric energy consumed by the small light bulb in 1 s is 1 J

D. The electric energy consumed by the small light bulb in 1 s is 1 J/s

2. Which of the following is the unit of electrical power ()

A.Volt

B.Ampere

C.Joule

D. Watt

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For more information about the "Electrical Power, Electrical Power and Electrical Power" PPT courseware, please click on the Electrical Power ppt Electrical Power and Electrical Power ppt tab.

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Update Time: 2024-11-14

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