"Exploring Joule's Law" Electric Energy and Electric Power PPT Courseware 2

Description

"Exploring Joule's Law" Electric Energy and Electric Power PPT Courseware 2

learning target:

1. Understand the relationship between heat production, resistance and current of electrical appliances.

2. Be able to design experiments to verify the relationship between the heat generation of the resistor and current, voltage, and resistance, and analyze the experimental data to draw conclusions.

3. The formula can be transformed and applied according to P=UI.

4. Know Joule's law and formulas, and learn to apply formulas for simple calculations. Know the various ways to dissipate heat from electrical appliances.

Detection Preview 1

1. Understand the relationship between heat production, resistance and current of electrical appliances.

2. Be able to design experiments to verify the relationship between the heat generation of the resistor and current, voltage, and resistance, and be able to analyze the experimental data to draw conclusions.

1. Thermal effect of electric current

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

Want to discuss

The electric stove wire and the wire pass the same current. Why does the electric stove wire glow red when hot, but the wire barely heats up?

What factors determine the amount of heat generated when electric current passes through a conductor?

Experiment 1: Study the relationship between electric heating and resistance

In the case of the same current and the same energization time, the greater the resistance, the more heat this resistance generates.

Experiment 2: Study the relationship between electric heat and electric current

When the resistance is the same and the power-on time is the same, the greater the current passing through a resistor, the more heat the resistor generates.

Introduction to Joule

James Prescott Joule (1818-1889), British physicist. He spent nearly 40 years conducting more than 400 experiments to study the relationship between heat and work. Through extensive experiments, the relationship between the heat generated by an electric current and the current, resistance, and energization time was first accurately determined in 1840.

2. Joule’s Law

1. content:

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

2. Formula: Q = I2Rt

3. Unit: Joule (J)

3. The relationship between electric energy and electric heat

1. In a purely resistive circuit (such as: electric heater, electric rice cooker, electric stove, etc.), when the current passes through the conductor, all the electrical energy is converted into internal energy without being converted into other forms of energy at the same time. In this way, the heat generated by the current Q It is equal to the consumed electric energy W, that is

Q = W= UIt = I²Rt=Pt=U²/R t

2. In a non-pure resistance circuit, such as when an electric fan is working, the electrical energy consumed is mainly converted into mechanical energy of the motor: electrical energy → internal energy + mechanical energy

At this time, Q=I2Rt (Joule's law) can only be used to calculate electric heat

Detection Preview 2

Know Joule's law and formulas, and learn to apply formulas to perform simple calculations. Know the various ways to dissipate heat from electrical appliances.

4. Utilization and prevention of electric heat

1. Utilization of electric heat

The advantages of electric heaters: clean and hygienic, no environmental pollution, high thermal efficiency, and can easily control and adjust the temperature.

1. Principle: It works by utilizing the thermal effect of electric current.

2. Core part: heating element, which is made of materials with high resistivity and high melting point.

3. The relationship between electric heat and electric power of electric heaters

Because the electric energy consumed in the electric heater is only used to generate heat, electric heat Q = electric power W

2. Dangers of electric heating

In many cases, we do not want the temperature of electrical appliances to be too high. For example: the back cover of the TV has many holes for ventilation and heat dissipation; when the computer is running, a micro fan must be used to dissipate heat in time, etc.

Practice in class

Sometimes the heating effect of electric current is good for us, and we use it; sometimes it is harmful to us, and we need to reduce the heating caused by electric current, or dissipate the heat as soon as possible.

(1) List two examples of using the thermal effect of electric current in life or production.

Electric blanket, electric soldering iron, electric rice cooker, electric heating incubator, etc.

(2) List two measures taken to prevent the harm caused by the thermal effect of electric current in life and production.

The computer host has a fan for heat dissipation; the heat dissipation window on the TV and the motor casing have many heat sinks.

Calculation exercises on Joule's law (electric heat)

1. The resistance of a certain conductor is 2Ω. When a current of 2A passes through it, how many joules of heat are generated in 1 minute?

Solution: Q=I2Rt=(2A)2×2Ω×60s=480J

If the current is doubled and other conditions remain unchanged, the electric heat will be ______ times the original

2. If a rice cooker with a rated power of 450W is used at the rated voltage, how much heat will it generate per minute?

Solution: The rice cooker is a pure resistance circuit

Therefore, Q=W=Pt=450W×60s=27000J

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Update Time: 2024-07-31

This template belongs to Physics courseware Guangdong and Shanghai Edition Ninth Grade Physics Volume 1 industry PPT template

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