"Exploring the Causes of Excessive Current in Household Circuits" Safe Electricity PPT Courseware 2

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"Exploring the Causes of Excessive Current in Household Circuits" Safe Electricity PPT Courseware 2

Electrical power and safe use of electricity

1. Disasters caused by improper use of electricity

A major electrical fire occurred at Moscow Friendship University, triggering a major rethink of the education system. Where is safety?

In the early morning of November 24, 2003, a major fire accident occurred in the No. 6 student dormitory of the Russian People's Friendship University located in southwest Moscow due to overloading of wires and a fire in the wires. 38 international students were killed and 168 were treated in the hospital. This is the electrical fire with the most widespread impact, the greatest losses, and the worst nature in Moscow in the past ten years.

According to the relationship between electric power, voltage and current: P=UI

The deformation formula can be obtained: I=P/U

It can be seen from the above formula:

When the voltage U of the household circuit is constant at 220V, the greater the electrical power P of the electrical appliance, the greater the current I in the circuit.

2. Safety device

1. The function of fuse

2. What material is the fuse made of? What are the characteristics of this material?

3. Can copper wire or iron wire be used instead of fuse? Why?

4. What is the basis for choosing a suitable fuse?

(1) Material: Made of lead-antimony alloy with high resistivity and low melting point

(2) Principle: When the current in the circuit is too large, the electrical energy is converted into heat and increases rapidly. The fuse melts due to the temperature increase, cutting off the circuit and playing a protective role.

(3) Installation: The fuse (or air switch) is usually installed on the household line after the electric energy meter.

(4) Choice: The rated current of the fuse in the household circuit should be equal to or slightly larger than the normal operating current of the circuit.

Why change the wire to a thicker one?

1. The length and material of the transmission wire remain unchanged. The purpose of changing the wire to a thicker one is to reduce the resistance of the wire. According to Q=I2Rt, when the transmission current and transmission time are constant, the heat generated on the transmission line decreases, which can reduce the power loss on the transmission line.

2. According to U=IR, if the resistance of the transmission conductor is high, part of the voltage will be diverted, so the voltage at both ends of the electrical appliance will not reach 220V, and the household appliance will not work properly.

3. The thicker the transmission wire, the greater the maximum current allowed to pass. Nowadays, more and more electrical appliances are used in household circuits, and the total power P is getting larger and larger, while the voltage U in household circuits is constant. According to I=P/U, it can be seen that the total current I is getting larger and larger. Wires may cause fire.

Xiaofang's home has two 40W energy-saving lamps, two 25W incandescent lamps, a 150W TV, and a 650W washing machine. The maximum current allowed by her household electric energy meter is 5A. Can Xiaofang’s electrical appliances be used at the same time? If I purchase another 700W rice cooker, can I use it at the same time?

Known: P1=40W×2 P2=25W×2 P3=150W

P4=650W I=5A P5=700W

Request: Mr. I

Solution: I total = P total/U

P total=P1+P2+P3+P4

=40W×2+25W×2+150W+650W=930W

I total=P total/U=930W/220V=4.2A<5A

If you buy another 700W electric cooker: P total 2 = 930W + 700W = 1630W

At this time, the current is Itotal2=Ptotal2/U=1630W/220V=7.4A>5A

They can be used at the same time at first, but they cannot be used at the same time after adding a rice cooker.

Are there any other solutions to this problem? Can you try it?

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"Exploring the Causes of Excessive Current in Household Circuits" PPT courseware on safe electricity use:

"Exploring the Causes of Excessive Current in Household Circuits" Safe Electricity Use PPT Courseware Learning Objectives 1. Know the relationship between the current in household circuits and the total power of electrical appliances. Understand that the total current in the circuit increases with the increase of the power of electrical appliances. 2. Know why a fuse is installed in the circuit...

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Update Time: 2024-10-02

This template belongs to Physics courseware Lu Jiao Edition Ninth Grade Physics Volume 1 industry PPT template

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