"Thermal Effect of Electric Current" Electric Work and Electric Power PPT Courseware 4

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"Thermal Effect of Electric Current" Electric Work and Electric Power PPT Courseware 4

Why do household appliances need to be stopped for a while after being used continuously for a long time?

Why do household appliances need to be powered on again after a period of time when they have been out of use for a long time?

Today we will specifically discuss the above-mentioned issues about electric heating.

learning target

⑴Know the heating effect of electric current.

⑵ Understand the heating principle of electric heaters and be able to give examples of utilizing and preventing electric heating.

⑶ Understand Joule's law, formulas and applicable conditions.

⑷We will conduct simple calculations on some household electric heaters.

⑸ Combined with the teaching of this section, cultivate a scientific attitude that values ​​experiments, respects facts and seeks truth from facts. By observing common electric heaters and their structures in daily life, students can cultivate their observation skills, combined with dialectical materialism education, to cultivate their ability to think and analyze problems critically.

Experience activities

Connect three resistors of 5 ohms, 10 ohms, and 20 ohms in series and connect them to the student's power supply. Adjust the power supply voltage to 9V. Observe and quickly touch the three resistors. What difference do you feel? Why?

The conductor has an obstruction effect on the current passing through it. This obstruction will convert electrical energy into internal energy, so the resistor will heat up after being energized. Moreover, for the same current and the same time, a resistor with a larger resistance will heat up more. People call this phenomenon the heating effect of electric current.

Common structural features of electric heaters

Students, think about it, what do the structures of so many electric heaters have in common?

⑴The main component of the electric heater is the heating element made of resistance wire.

⑵The heating elements are made of materials with high resistivity and high melting point.

do you know?

Why should electric heaters be made of resistance wire with high resistivity and high melting point?

Why should the resistance wire of an electric heater be wound on insulating material?

What are the advantages of electric heaters over other heaters?

Students, after thinking about it, discuss this issue!

⑴ Cleanliness and hygiene;

⑵Almost no environmental pollution;

⑶High thermal efficiency;

⑷The temperature can be easily controlled and adjusted.

How to observe electric heat:

Method 1: Heat the electric heating wire and light the match

advantage:

⑴The phenomenon is intuitive and obvious;

⑵The equipment is simple and easy to prepare;

⑶The experiment time is short and the operation is simple.

shortcoming:

The phenomenon is easily disturbed by factors such as matches, placement location, environment (such as air flow);

Method Two

The heating wire heats up the kerosene and expands it.

advantage:

⑴The phenomenon is intuitive and precise;

⑵ Less interference from the environment.

shortcoming:

⑴The phenomenon is subtle and difficult to see from a distance;

⑵The equipment is complex and difficult to prepare;

⑶The experimental time is slightly longer.

Understand Joule’s Law

The British physicist Joule spent nearly forty years exploring the "relationship between work and heat". He was not afraid of difficulties and worked hard. He devoted almost his entire life to promoting the progress of human society and science. His deeds are very touching. . In order to commemorate this great scientist, "Joule" is used as a unit of work or energy in physics.

Joule's law

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

Formula: Q=I2Rt

The units of the physical quantities in the formula are:

I→A, R→Ω, t→S, Q→J

Note: Joule's law is an experimental law. Further experiments have proved that Joule's law is applicable to pure resistive circuits.

Summary of this lesson

1. Know the thermal effect of electric current; know the heating principle of general electric heaters; and be able to perform simple calculations on some household electric heaters.

Current heating effect, heating principle of electric heater, characteristics of resistance wire materials

Simple household electric heater calculations.

2. Explore the factors that determine electric heating, understand and correctly apply Joule’s law

What factors are related to electric heat, Joule's law, formulas, units;

Applicable conditions of Joule's law and calculation of electric heat

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Update Time: 2024-07-30

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