"Joule's Law" Electric Power PPT Teaching Courseware

Description

"Joule's Law" Electric Power PPT Teaching Courseware

Part One: Knowledge Management

1. heating effect of electric current

Definition: Electrical energy is converted into internal energy when current passes through a conductor.

Application: electric stove, electric iron, rice cooker, electric blanket.

2. Joule's law

Content: The heat generated by current passing through a conductor is directly proportional to the square of the current ________, directly proportional to the resistance of the conductor ______, and proportional to the energization time ______.

Formula: Q=I2Rt. In a pure resistance circuit, the work done by the current converts all the electrical energy into internal energy, that is, all the work done by the current is used to generate heat. Then W=Q, then there is the formula W=Q=I2Rt=UIt= U2Rt=Pt.

Note: If a "purely resistive" electrical appliance such as an electric stove or an electric soldering iron is connected to the circuit, when the current passes through, all the electrical energy consumed is converted into internal energy. At this time, the electrical energy consumed is equal to the electric heat, that is, W = Q , electric heat can be calculated using the formula for calculating electrical energy. When a motor is connected to the circuit, most of the electrical energy consumed is converted into mechanical energy, and electric heat only accounts for a small part, that is, W>Q, so Joule's law can only be used to calculate electric heat.

3. Utilization and control of electric heat

Usage: To manufacture electric heaters. The heating element is made of alloy wire with high resistivity and high melting point wound on insulating material. Its advantages are: ① clean and hygienic, no environmental pollution; ② high thermal efficiency; ③ can easily control and adjust the temperature.

Control: Install fans and heat dissipation windows to speed up heat dissipation and prevent electric heat from harming electrical appliances.

Joule's Law PPT, Part 2: Classification and Research

Type One: Exploring Joule’s Law

[2017 • Liuzhou, Guangxi Province

(1) In the experiment shown in Figure A, the amount of heat generated by the current is compared through the changes in the thermometer indication.

(2) In Figure A, in order to compare the amount of heat generated by the two resistance wires after passing current, two bottles a and b are filled with kerosene with the same initial temperature and quality. The temperature of the kerosene in bottle a rises faster.

(R nickel-chromium alloy wire>R manganese copper wire)

[Analysis] (1) The amount of heat generated by the two resistance wires is reflected by the change in the thermometer indication.

(2) When exploring the amount of heat generated by two resistance wires after passing current, the quality of kerosene and the initial temperature should be controlled to be the same. As can be seen from the figure, when the current is the same, the resistance of a is greater than the resistance of b. According to Joule's law, a The more heat is generated, the temperature rises quickly.

(3) If the flask is filled with water, it can be seen from Q=cmΔt: When the same mass of water and kerosene absorb the same amount of heat, due to the larger specific heat capacity of water, the temperature will rise less, and the reading of the thermometer will not change. obvious.

(4) When the resistance and energization time are the same, the greater the current passing through the conductor, the more heat is generated.

(5) In order to ensure that the current passing through the two resistors is always equal, the resistors are connected in series; and at the same time to ensure that their energization time is also equal, the heat generated in the conductor is only related to the resistance. For this purpose, the controlled variable method is used; kerosene absorbs heat The amount is reflected by the change in the thermometer indication, which is the conversion method adopted.

[Method Summary] When exploring the experiment: (1) First analyze the connection method of each resistor, and then analyze the current characteristics of series and parallel circuits combined with the application of Ohm's law.

(2) The amount of heat absorbed cannot be directly observed, but the change in liquid temperature can be reflected by the change in the thermometer indication, which embodies the idea of ​​conversion.

Type 2 Application of Joule’s Law

[2018•Linyi, Shandong]Xiao Ming’s mother bought an electric footbath for her grandma. The interior consists of a heating system and a massage system. The heating resistor of the heating system has a rated voltage of 220 V and a rated power of 605 W. ask:

(1) When Xiao Ming helps grandma soak her feet, she adds 6 kg of water with an initial temperature of 20 ℃ into the foot bath basin. The heating resistor of the heating system works normally for 15 minutes to heat the water to 40 ℃. The heat absorbed by the water during this heating process is How many? How much power is consumed? [cWater=4.2×103 J/(kg·℃)]

(2) When the actual voltage of Xiao Ming's home is 200 V, what is the actual power of the heating resistor?

(3) The working voltage of the motor in the foot bath massage system is 12 V (the massage system converts the AC voltage to 12 V), the working current is 4 A, and its resistance is 0.5 Ω. How much power is lost due to heat generation during the operation of the motor?

Joule's Law PPT, Part 3: Assessment in class

1. [2018•Shandong Weifang]The physicist who was the first to accurately determine the relationship between the heat generated by current and current, resistance and energization time was (B)

A． Ohm b. joule

C. Oster D. faraday

2. [2018•Hunan Shaoyang]A refrigerator, a computer and an electric blanket with specifications of "220 V 180 W" are connected to the same household circuit respectively. If the power-on time is the same, then Which of the following statements is correct (C)

A． Refrigerators generate the most heat

B． Computers generate the most heat

C. Electric blankets produce the most heat

D. All three generate the same amount of heat

3. [2018•Guangdong Shenzhen]When two heating wires with the same resistance are connected in series to a circuit, the time it takes to boil a pot of water is t0. If these two heating wires are connected in parallel to the same circuit, then The time required to boil the same pot of water is (not counting heat loss) (C)

A． t0 B. 12t0

C.14t0 D. 2t0

4. [2018•Shandong Rizhao]Using the two diagrams A and B, we can study the factors related to the amount of heat generated when the current passes through the conductor. After ensuring that the voltage at both ends of each circuit remains unchanged and the power is supplied for the same time (C)

A． In Figure A, the ratio of the heat generated by the left and right resistors is 2:1

B． In Figure A, the ratio of the heat generated by the left and right resistors is 1:4

C. In Figure B, the ratio of the heat generated by the left and right resistors is 4:1

D. In picture B, if the resistor on the right container is removed, the heat generated by the heating resistor on the right becomes 4 times the original value.

5. [2018•Liaoyang, Liaoning]The experimental device shown in the picture can be used to explore the relationship between the heat generated by the current passing through the conductor and the resistance when the energization time is the same. Connect the device to a power supply with a voltage of 3 V and energize it for 2 minutes. The heat generated by the current passing through the resistor R2 is 24 J.

Joule's Law PPT, Part 4: Layered Operations

1. [2018•Beijing]Among the following electrical appliances, the one that uses the heating effect of current is (　A　)

A． Electric heater

B． calculator

C. TV set

D. laptop

2. [2019•Beijing Chaoyang District] Among the following situations, the one that belongs to preventing electric heating hazards is (　D　)

A． incandescent light bulb

B． Cook rice with rice cooker

C. Use electric heaters to keep warm in winter

D. There is a small fan inside the computer case

3. [2018•Guangdong Shenzhen]The picture shows the experimental device of "Exploring Joule's Law". Two identical flasks are sealed with kerosene with the same initial temperature and equal quality. After being powered on for a period of time, the liquid level in the glass tube on the right side is higher than that on the left side. Which of the following statements is correct (D)

A． The amount of heat generated by the current is judged by the height of the liquid level in the glass tube. This method is the controlled variable method.

B． The resistance value of the resistance wire on the right side is smaller than that on the left side

C. The current passing through the resistance wire on the right side is smaller than that on the left side

D. This device is used to explore the relationship between the amount of heat generated by current passing through a conductor and the size of the resistance.

4. [2018•Luzhou, Sichuan]The main component of a household washing machine is the motor. If the current passing through a washing machine when operating normally in a 220 V circuit is 2 A, and the motor coil resistance is 4 Ω, then the current passing through it per minute The heat generated by the coil is (A)

A． 960JB. 7.26×105 J

C. 2.64×104 JD． 440 J

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Update Time: 2024-10-24

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