"Causes of Excessive Current in Household Circuits" Daily Electricity PPT Courseware 4

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"Causes of Excessive Current in Household Circuits" Daily Electricity PPT Courseware 4

1. The impact of the total power of household appliances on household circuits

What changes will be brought to the circuit as the electrical power becomes larger?

Change in voltage (U)? Change in current (I)?

The voltage in household circuits remains unchanged at 220V. Because P=UI, I=P/U. As the electrical power P increases, I becomes larger. The increase in electrical power will cause the current in the circuit to increase.

Therefore: blindly using too many electrical appliances at the same time - the power consumption becomes larger - the current is too large - it is easy to cause a fire.

2. Causes of excessive current in household circuits

1. The total power of electrical appliances in the circuit is too large, causing excessive current in the circuit.

2. Short circuit causes excessive current in the circuit.

Short circuit---the total resistance is very small---the current in the main circuit is too large.

3. Understand the circuit safety guard—safety device

1. The function of the fuse: to provide safety protection for the circuit

2. Characteristics of fuse materials:

Fuses are made of a lead-antimony alloy that has a high resistance and a low melting point.

3. Fuse principle:

The resistance is large. When the current in the circuit is too large, the fuse generates more heat, causing its temperature to reach the melting point. Then the fuse blows and automatically cuts off the circuit to ensure the safety of the circuit and electrical appliances and avoid fires.

4. Principle for selecting fuse: Make its rated current equal to or slightly greater than the maximum current when the circuit is working normally.

5. Be connected to the live line

Notice:

(1) The fuse cannot be too thick

The thicker the fuse, the greater the rated current and fusing current;

(2) It is prohibited to use iron wire or copper wire as a substitute for fuse. They have high melting points and low resistance. If the current is too large, it will not fuse and it will not function as an insurance.

Class exercises

1. The fuse is installed on the main road. There are 10 "220V 40W" electric lamps and 10 "220V 25W" electric lamps in a factory. Then when all these lamps are working, the current passing through the fuse is about ( )

A. 0.29A B. 1.14A C. 1.82A D. 2.95A

2. The main function of the fuse is ( )

A. Ensure that the voltage of the circuit remains unchanged

B. Ensure that the current of the circuit remains unchanged

C. Protect the safety of the human body

D. Automatically cut off the circuit when the current intensity exceeds the specified value

3. On the newly assembled home circuit experiment board, as soon as the switch is turned on, the fuse blows and the light bulb does not light up. The reason may be ( )

A. The tungsten filament in the light bulb is broken B. The switch has poor contact

C. The neutral line and live line are short-circuited. D. The circuit is not connected.

4. The cause of excessive current in household circuits cannot be ( )

A. Short circuit between live wire and neutral wire B. Poor wiring of electrical appliances and circuits

C. High-power electrical appliances are connected. D. The total resistance in the circuit is too small.

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Update Time: 2024-10-05

This template belongs to Physics courseware People's Education Edition Ninth Grade Physics Complete Book industry PPT template

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