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

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

learning target

1. Know the relationship between the current in the household circuit and the total power of the electrical appliances, and understand that the total current in the circuit increases as the power of the electrical appliances increases.

2. Know why a fuse is installed in the circuit and why it can be "safe".

In recent years, many urban and rural areas in my country have been undergoing transformation of power supply lines. One of the contents is to replace the wires with thicker ones and the current allowed by the electric energy meters to be replaced with larger ones.

Based on your knowledge of household appliances, can you deduce the relationship between electrical power and current?

Is it what you thought?

1. The length of the transmission wire remains unchanged and the material remains the same. Only the wire is replaced with a thicker one in order to reduce the resistance of the wire. If the current on the transmission line remains unchanged and the resistance decreases, according to P=I2R, it can be seen that the thermal effect on the transmission line is reduced, which can reduce the power consumption on the transmission line.

2. The thicker the transmission conductor, the greater the current it carries. According to P=UI, I=P/U. The voltage of the household circuit is certain. The greater the power P, the greater the current I in the circuit. Therefore, the transmission conductor needs to be Change to a thicker one.

The relationship between electrical appliance current and total power

Total power of electrical appliances:

P total=P1＋P2＋P3

=U（I1＋I2 +I3）=UI total

Because the power supply voltage U =220V in household circuits remains unchanged,

From I total =P total/U, it can be seen that the greater the P total, the greater the I total.

1. The relationship between power P and current I

1. From P=UI, I=P/U, U is certain, the greater P, the greater I.

2. What is the cause of excessive current in household circuits?

One: The total power of electrical appliances is too large. Two: A short circuit occurs.

3. When decorating circuits, be sure to consider the endurance capabilities of transmission lines, energy meters, and fuses.

2. The function of fuse

Why do fuses function as insurance?

The fuse uses the thermal effect of current to work, just like an automatic switch. When the current is too large, it will automatically fuse and cut off the circuit, playing an insurance role.

What material are fuses made of?

Why do fuses have different thicknesses?

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

When the material and length of the fuse are constant, the thicker the fuse, the smaller the resistance, and the melting point of the fuse is the same. According to Q=I2Rt, when current flows through the fuse, a fuse with a small resistance needs a larger current to melt. So the thicker the fuse, the smaller the resistance, and the higher the rated current.

The fuse in your home has blown, what should you do?

Steps:

1. Disconnect the main source at home

2. Find and eliminate faults

3. Replace the fuse with the same specification

4. Close the beginning

Note: Replace the fuse with the same specification, and do not use iron wire or copper wire to replace the fuse.

3. Air switch

(1) Function: When a short circuit, overload, etc. causes excessive current in the line, the safety device consisting of the iron core, coil, armature, and spring will automatically trip, that is, the switch will automatically open and cut off the circuit, commonly known as Trip.

(2) How to use: After disconnecting, wait until the fault is eliminated, and then close the knife switch.

6. Read the short article (excerpted from (CCTV (China News) summary on August 3)) and answer the questions:

The large-scale installation and use of air conditioners has brought coolness to everyone, but at the same time, it has also caused a rapid increase in the electricity load in Beijing. Since August 1st, the Beijing Power Supply Customer Service Center’s power fault repair phone has been ringing non-stop. The person in charge explained: “A considerable number of residences have not undergone line modifications, so the current summer high temperatures and heavy loads, the electricity consumption is It is very difficult because these lines are relatively old and carry a very small load. If all air conditioners, electric water heaters, and other household appliances are turned on, the lines will definitely be overwhelmed. Therefore, we call on you to avoid peak electricity consumption as much as possible and reduce the power consumption at home. Other loads.”

(1) Which physical quantity we study should correspond to the "electrical load" in the article?

(2) What do you understand by the words "high temperature in summer", "large load" and "difficulty in using electricity" in the article?

(3) What does "line reconstruction" in the article mean?

(4) Please analyze: What are the possible consequences of concentrated and large-scale use of air conditioners?

Practice questions

1. When classmate Xiao Ming was watching TV at home during the winter vacation, he took out an electric heater to keep warm. When he inserted the plug into the socket, he heard a "down" sound, and at the same time, a puff of black smoke came out of the socket, and the TV and lights also went out... The consequences of this phenomenon are:

A.The TV is burned out

B The electric heater burned out

C air switch is disconnected

D The filament is burned out

2. In life, we will encounter these situations: (1) Two wires in the switch collide; (2) Two wires in the plug collide (3) High-power electrical appliances are added to the circuit (4) ) Damage to the insulation of outdoor transmission lines. In the above situation, what may cause the fuse in the home circuit to blow?

A(1)(2)(3)

B(2)(3)

C(2)(4)

D(1)(4)

3. When the electrical appliances of a certain family are working normally, the electric power is as shown in the following table:

(1) When all electrical appliances are working normally at the same time, what is the total current of the household circuit?

(2) On average, all electrical appliances work less than 1 hour a day. How much electricity can this family save every month (30 days)?

(3) If the specifications of all electric energy meters in your home are "220V, 5A", explain how to use these appliances reasonably.

Consolidation exercises:

1. If you want to install a "220V, 25W" light bulb 25, you should only choose which of the following fuse specifications ()

The fuse current of A is 3AB and the rated current of B is 3A.

C fuse current is 5AD; D rated current is 5A

2. The total power of a certain household electrical appliance does not exceed 2000W. The appropriate electric energy meter that can be selected is ()

A.380V5AB.380V10A

C.220V10AD.220V10A

3. In a certain household circuit, it is known that two lamps emit light normally. If an electric iron is used, the circuit's ()

A. The total current becomes larger. B. The total voltage becomes larger.

C the total resistance becomes larger D the total power becomes larger

4. The reason why fuses in household circuits cannot be replaced by copper wires is ( )

A. High resistivity, high melting point. B. High resistivity, low melting point.

C has low resistivity and high melting point D has low resistivity and low melting point

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Update Time: 2024-07-02

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