"Causes of Excessive Current in Household Circuits" Daily Electricity PPT

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"Causes of Excessive Current in Household Circuits" Daily Electricity PPT

Part One Content: Basic Knowledge Key Points

Knowledge point 1: The impact of the total power of household appliances on household circuits

1. CCTV's "Advertise It" column once played a public service advertisement (as shown in the picture). The TV in the picture is connected in parallel with other electrical appliances. When the electrical appliances connected to the circuit through the socket work at the same time, the total power consumed in the circuit is too large, causing the current in the main circuit to be too large. According to Joule's law, the current on the main circuit generates too much heat, causing the temperature of the wire to rise sharply. If it rises, it will burn out the wires of sockets and trunk circuits, easily causing a fire.

2. Xiao Ming was watching TV with the air conditioner on at home. When his mother was just using the rice cooker to cook, the automatic air switch at home "tripped". The reason for the "trip" may be that the total power of the electrical appliances was too high. The picture shows the nameplate on Xiao Ming's automatic air switch. From this, it can be judged that the total power of electrical appliances allowed by his circuit is 2200W.

3. The lights in the household circuit are dim, but the electric energy meter dial rotates very fast. This phenomenon indicates that what is happening in the circuit may be (B)

A. Short circuit B. Total power is too large

C. Leakage D. Insufficient power supply voltage

Knowledge point 2: The impact of short circuit on household circuits

4. The following phenomena can cause fires in household circuits: ①②④ (fill in the serial number).

①The total power of the electrical appliance is too large; ②Short circuit; ③Two wires in the switch touch; ④Two wires in the plug touch

5. The lights in a classmate’s home are working normally. When he inserts the “220 V 16 W” desk lamp into the socket and turns on the desk lamp switch, all the indoor lights go out. The reason for this phenomenon may be (B)

A. Short circuit at the socket B. Short circuit at the lamp head of the desk lamp

C. Open circuit at the socket D. Open circuit at the lamp head of the desk lamp

Knowledge point 3: The function of fuse

6. Regarding the replacement of fuses, which of the following statements is correct (C)

A. Use aluminum wire instead

B. For insurance, try to choose a thick fuse

C. Choose a fuse with a rated current equal to or slightly larger than the maximum normal operating current in the circuit.

D. Choose a fuse with a rated current equal to or slightly smaller than the maximum normal operating current in the circuit.

7. In order to prevent danger due to excessive current, fuses must be installed in household circuits to protect electrical appliances or personal safety. Which of the following statements is correct (C)

A. Human body electric shock is the only cause of excessive current in household circuits

B. The specifications of the fuse can be chosen arbitrarily.

C. The material used to make the fuse has a lower melting point and a higher resistance.

D. The material used to make the fuse has a higher melting point and lower resistance.

PPT on the causes of excessive current in household circuits, part 2: improvement of comprehensive capabilities

8. The picture shows two situations that cause wire burning in household circuits. The situation shown in Picture A is overload, and the situation shown in Picture B is short circuit (please fill in "A" or "B" for both).

9. In the circuit shown in the figure, the length and thickness of the fuse AB and the copper wire CD are the same. After turning on the power, adjust the sliding rheostat and find that the fuse blows first. The reason is that the melting point of the fuse is lower (please fill in "high" or "low") and generate more electric heat in the same time (please fill in "more" or "less").

10. A short circuit occurs in an electrical appliance at home and the fuse blows immediately. Use the following method to detect it. As shown in the figure, turn off the switches of all electrical appliances and use an ordinary incandescent lamp L as a "check light" with the blown fuse. Connect in parallel, and then only close S and S1. If the lamp L glows normally, it means that the lamp L1 is short-circuited; only close S and S2. If the lamp L emits dark red light (the light is abnormal), it means that the lamp L2 is normal (please fill in "Normal" for both ""short circuit" or "open circuit").

11. Regarding household electricity consumption, which of the following statements is correct (B)

A. If the current in the household circuit is too large, there must be a short circuit in the circuit.

B. The greater the total power of the electrical appliances connected to the circuit, the greater the current in the main circuit.

C. If the fuse is blown, you can use copper wire or iron wire to replace it.

D. After the air switch trips, just close the switch again.

12. Part of the circuit of a certain household is as shown in the figure, in which electrical appliances and switches are installed in places A and B respectively. For this circuit, the following statement is correct (C)

A. The fuse on the live line should be modified to the neutral line

B. Electrical appliances should be installed in place A, and switches should be installed in place B.

C. A fuse connected in series in the circuit can prevent the current from exceeding the specified value and causing a fire.

D. The fuse is characterized by a higher melting point

13. If the following three situations occur in household circuits: ① two wire ends in the lamp holder collide; ② two wire ends in the switch collide; ③ two wire ends in the two-hole socket collide, which will cause the circuit to malfunction. The fuse in the middle is blown (B)

A.①② B.①③

C.②③ D.①②③

14. Fuses of different thicknesses allow different currents to pass through. The fuse in the main fuse box of a teaching building allows a current of 25 A. There are 20 classrooms in the building. Each classroom is equipped with 6 40 W fluorescent lamps. When all the fluorescent lamps are on, 100 W can be connected. W electric fan (A)

A.7 units B.8 units C.9 units D.10 units

PPT on the causes of excessive current in household circuits, part 3: Expansion of research and breakthroughs

16. The currently developed superconducting current limiter has zero resistance when the current is less than a certain value; when the current is greater than a certain value, its resistance is a certain value. When the superconducting current limiter is connected to the circuit, when the current suddenly becomes larger than a certain value, the superconducting current limiter instantly has a certain resistance value to protect the entire circuit. As shown in Figure A, the resistance of a certain superconducting current limiter changes with the current. As shown in Figure B, the superconducting current limiter and electrical appliance M are connected in series and then connected to a high-voltage power supply with a voltage of 5×104 V. beg:

(1) When the current in the circuit is 30 A, how much electrical power is consumed by electrical appliance M?

(2) When the electrical appliance M is short-circuited, the superconducting current limiter can protect the circuit. R0 cannot be greater than a certain value. What is this value?

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Update Time: 2024-07-03

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