"Problems with Multiple Gears of Electrical Appliances" Electric Power PPT

Description

"Problems with Multiple Gears of Electrical Appliances" Electric Power PPT

Topic overview

The problem of multiple gears of electrical appliances is a comprehensive problem that integrates electric heat, electric power and electric power. It is the focus and difficulty of electrical problems. The main types include multi-gear problems with electrical appliances and multi-gear problems with electric heaters.

The key to solving the problem of multiple gears of electrical appliances is to understand the working characteristics of the electrical appliances and the physical quantities such as power, current, resistance, etc. corresponding to different gears. For example, the operation of a soybean milk machine mainly includes the two processes of heating and beating, the operation of a fully automatic washing machine mainly includes the two processes of washing and dehydration, and the operation of a hair dryer mainly determines whether to blow cold air or hot air, etc.

To answer questions about electric heaters, two key points need to be grasped.

Key point one: Correctly determine the gear position of the electric heater. Generally speaking, electric heaters usually have "high temperature gear", "medium temperature gear" and "low temperature gear". According to the formula of electric power P=U2R, when the voltage is constant, the greater the resistance, the smaller the electric power. The smaller the resistance, the greater the electric power. is large, so the total resistance of the high-temperature block is the smallest, and the total resistance of the low-temperature block is the largest.

Key point two: clarify the structure of the electric heater in different gears.

(1) Short-circuit type: As shown in Figure A, two resistors are connected in series, and switch S1 is connected in parallel with one of the resistors. When both switches are closed, resistor R2 is short-circuited and only one resistor works. At this time, it is a high temperature block; When switch S is closed and S1 is open, the two resistors are connected in series, and the total resistance is the largest, which is the low temperature gear.

(2) Single-pole double-throw type: As shown in Figure B, place the main working resistor R1 on the main road, use only wires for one branch, and connect additional resistors to the other branch. When the switch S is thrown toward the additional resistor branch, the two resistors are connected in series, which is the low-temperature block; when the switch S is thrown toward the pure wire branch, only the main resistor R1 works, which is the high-temperature block.

(3) Parallel type: As shown in Figure C, two resistors are connected in parallel. The switch S1 controls the two resistors, and the switch S2 controls the resistor R2. When the switches S1 and S2 are closed at the same time, both resistors work. At this time The total resistance is small, which is the high temperature gear; when the switch S1 is closed and S2 is open, only the resistor R1 works. At this time, the total resistance is large, which is the low temperature gear.

Type 1: Multi-gear problem of electric heater

1. As shown in Figure 3-ZT-1, the resistors R1>R2, and the power supply voltages are all U. During the same time, the total heat generated by the resistors in the circuit in Figure A is QA, and the total heat generated by the resistors in the circuit in Figure B is QA. is QB, the total heat generated by the resistor in the circuit in Figure C is QC, and the total heat generated by the resistor in the circuit in Figure D is QD, then ()

A.Q A＞Q B＞Q C＞Q D

B.Q Ding>Q ​​C>Q B>Q A

C.Q Ding>Q ​​B>Q A>Q C

D.Q A＞Q C＞Q B＞Q D

2. When the power supply voltage is constant U, within the same time, when two resistors are connected in series, the total resistance is the highest, the total heat generated is the highest, and the heating power is the highest. When the two resistors are connected in parallel, the total resistance is the highest. , the total heat generated is the most ________, and the heating power is the most ________. If the electric heater is in the state of two resistors connected in series, the electric heater is generally in the ________ (optional "high", "medium" or "low") gear; if the electric heater is in the state of two resistors in parallel, the electric heater is generally in_ _______ (optional "high", "medium" or "low") gear.

3. Figure 3-ZT-2 shows the working circuit diagram of the electric kettle. Close the switch S1. When the electric kettle is in the heating state, the switch S2 is in the _________ state. If the power of the electric kettle in the heating state is 1210 W, then the resistance R1 = ________Ω. If the total power of the electric kettle in the keeping warm state is 10% of that in the heating state, then the power of R2 is ________W.

4. The circuit of an insulated electric kettle is shown in Figure 3-ZT-3. S is the temperature control switch. The electric kettle is marked with "220 V 1000 W". The electric power of R1 is 12.1 W when insulated. Question: (Not considered Effect of temperature on resistor value)

(1) When switch S is connected to a, the electric kettle is still in the heat preservation state.

Is it in a heated state? Why?

(2) In the heating state, the electric kettle works normally

What is the current?

(3) What are the resistance values ​​of R1 and R2?

5. Students from a certain technology production team used two sections of electric heating wires R1 and R2 with different resistances to design an electric heater with three gears: high, medium and low. The circuit diagram is shown in Figure 3-ZT-4, where R1= 2R2. Under safe conditions, use three gears to heat water with a mass of 2 kg in the same container. [cwater=4.2×103 J/(kg·℃)]

Keywords: Free download of PPT courseware for ninth-grade physics from the People's Education Press, PPT download on multiple gears of electrical appliances, PPT download of electrical power, .PPT format;

For more information about the PPT courseware "Multi-gear Problems in Electrical Power Appliances", please click the "Multi-gear Problems in Electrical Power PPT Electrical Appliances" ppt tag.

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Update Time: 2024-09-11

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