"Joule's Law" Electric Power PPT Courseware 7

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"Joule's Law" Electric Power PPT Courseware 7

Thermal effect of electric current:

In life, many electrical appliances will generate significant heat after being powered on. This phenomenon is called the heating effect of current.

When electric current passes through a conductor, electrical energy is converted into heat. This phenomenon is called the thermal effect of electric current.

The heat generated is represented by Q

Among the following electrical appliances, which one uses the heating effect of electric current ( )

A. TV B. Electric blanket C. Washing machine D. Soldering iron

1. What is the relationship between the heat generated by current passing through a conductor and time?

Since electric current has a thermal effect, the nickel-chromium alloy resistance wire will generate heat after being energized, causing the liquid in the flask to expand due to heat, causing the liquid in the glass tube to rise to a certain height. The more heat the resistance wire generates, the more liquid in the glass tube will rise. The higher the liquid injection, so in this experiment we use ________ to determine the amount of heat generated by the current.

We can imagine: as time goes by, when other conditions are constant, the longer the time and the higher the liquid injection, the more heat we say the current generates.

When other conditions are constant, the longer the energization time, the more heat the conductor generates.

2. What is the relationship between the heat generated by current passing through a conductor and resistance?

When the time and current are the same, the greater the resistance, the more heat is generated.

3. What is the relationship between the heat generated by current passing through a conductor and the current?

As shown in the picture: Put two resistance wires with the same resistance value into two bottles and connect them to two circuits with different voltages. The current flowing through ____ is large. From the experimental phenomenon: the liquid injection in B rises high. . What conclusions can you draw?

When the time and resistance are the same, the greater the current, the more heat is generated.

Joule's Law: (P49)

The heat generated by current flowing through a conductor is proportional to the square of the current, the resistance of the conductor, and the time it takes to conduct electricity.

Joule's law formula: Q=I2Rt

4. Example analysis

Example 1: Why does the electric stove turn red when it is hot, but the wire barely heats up?

Answer: Because the wire and the electric furnace wire are connected in series, I wire = I electric furnace wire

R electric furnace wire > R wire. According to Joule's law Q=I2Rt, it can be seen that the heat generated by the current passing through the electric furnace wire is large in the same time, so the electric furnace is red with heat but the wire generates almost no heat.

Theoretical derivation of Joule's law

When a current passes through a conductor, if all the electrical energy consumed is converted into heat without being converted into other forms of energy at the same time, then the heat Q generated by the current is equal to the electrical energy W consumed.

That is: Q = W= Pt= UIt= IR It= I2Rt

Reason: The wire resistance is much smaller than the electric furnace wire resistance and generates less heat.

1. The heating effect of electric current is the phenomenon that _____ is converted into ____ when electric current passes through a conductor. An electric heater is a heating device made of _______ that uses electric current.

2. In the experiment of "studying the relationship between the heat generated by electric current and the current", _____ and _____ should be kept constant, and _________ should be changed.

3． In the experiment, in order to compare the relationship between the heat generated by the current passing through two different sections of metal wire and the resistance, the same physical quantity should be maintained during the experiment ( ).

A. The current passing through them and the voltage across them

B. the current passing through them and their resistance

C. The current passing through them and the energization time

D. The current passing through them, the voltage applied across them and the energization time

4. Connect a "220 V, 100 W" electric fan, a "220 V, 100 W" charger, and a "220 V, 100 W" soldering iron to the 220 V power supply respectively. In the same period of time, the most heat generated by current passing through them is ( ) the electrical energy consumed ( )

A. Soldering iron b. charger

C. Electric fan D. As much

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Update Time: 2024-10-03

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