"Causes of Excessive Current in Household Circuits" Daily Electricity PPT Courseware 3

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"Causes of Excessive Current in Household Circuits" Daily Electricity PPT Courseware 3

Discuss the "thinking about discussion" of the textbook and think about:

1. Why should the transmission lines be replaced with thicker ones? Change the calibrated current of the energy meter to a larger one? What's the point of doing this?

2. Can you deduce the relationship between electrical power and current in the circuit? Feel free to express your views and opinions.

learning target

1. Know that excessive total power of electrical appliances and short circuit phenomena will cause excessive current in household circuits;

2. Know the role of fuses and air switches in circuits;

3. Establish safety awareness in the process of using electricity in daily life.

1. Causes of excessive current in household circuits

1. Short circuit

think:

Why does a short circuit cause excessive current? State the basis for your judgment.

In the case of a short circuit, according to Ohm's law: because the voltage U is constant, the resistance R is very small when a short circuit occurs; therefore, the current I in the circuit is very large.

?Think about it

1. What phenomenon did you see? Was the bulb damaged during the short circuit?

2. Why does short circuit cause fire? How to prevent short circuits in daily life?

2. The total power of electrical appliances is too large

think:

Excessive total power of electrical appliances can also cause excessive current. Can you tell me the basis for your judgment?

Can you confirm your judgment with experiments?

Phenomenon: The more bulbs connected in parallel, the larger the ammeter indication will be. When enough bulbs are connected in parallel, the fuse will blow.

Analysis: The light bulbs are connected in parallel. The more light bulbs connected in parallel, the greater the total power in the circuit. According to I=P/U, it can be seen that U is certain, P is large, and I is also large, so the more light bulbs connected in parallel, the greater the main circuit current.

2. Fuse

Look at page 111 of the textbook, think about it and discuss in groups:

1. Why does the fuse automatically blow when the current is too large?

2. In order to achieve the purpose of insurance, what characteristics should the material of the fuse have?

3. Can I switch to fuses of different specifications at will, or use iron wire or copper wire instead of the fuse?

1. Function: When the current is too large, the fuse blows and cuts off the circuit, which plays a protective role.

2. Principle: Thermal effect of electric current.

3. Material: lead-antimony alloy with high resistivity and low melting point.

Note: Never use copper wire or iron wire instead of a fuse!

Class summary

1. The reason for excessive current in household circuits is: short circuit or the total power of electrical appliances is too large.

2. Safety device in household circuit: fuse or air switch.

Class exercises

1. The reason for excessive current in the circuit is ( ) or ( )

2. What causes fuses to blow in household circuits ( )

A. The fuse is too thick and unqualified

B. All electrical appliances work at the same time

C. It must be caused by a short circuit

D. High-power electrical appliances may be connected

3. The fuse in the household circuit is broken. The following reasons are impossible: ( )

A. The power of the electrical appliances in the home is too high. B. The two wire heads in the pull switch touch.

C. The specifications of the fuse are inappropriate and the fusing current is too small. D. The two wire heads in the plug touch.

Operation:

1. Exercises 1 and 2 in this section.

2. Understand the power of all household appliances in your home, calculate the total current passing through the fuse when the appliances are working at the same time, and compare it with the calibrated current on the energy meter. What measures will you take to ensure safe electricity use?

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Update Time: 2024-06-27

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

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