"Electric Energy and Electric Power" Electric Power and Electric Power PPT Courseware 5

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"Electric Energy and Electric Power" Electric Power and Electric Power PPT Courseware 5

Review of Three Experiments on Electricity and Magnetism

1. Oersted’s experiment

There is a magnetic field around a current-carrying conductor, and the direction of the magnetic field is related to the direction of the current.

2. Experiment on the effect of magnetic field on electric current

A current-carrying conductor is acted upon by a force in a magnetic field, and the direction of the force is related to both the direction of the current and the direction of the magnetic field.

3. Experiment on electromagnetic induction phenomena

When a part of a conductor in a closed circuit moves in a magnetic field to cut the magnetic field lines, a current will be generated in the conductor. The direction of the current is related to the direction of the magnetic field and the direction of motion.

Exam syllabus requirements

1. Understand electrical energy and electrical power

2. Be able to use an energy meter to measure electrical power

3. Be able to calculate electrical power

remember

1. What is “doing work”?

Answer: When a force acting on an object causes the object to pass a certain distance in the direction of the force, it is said that the force has done work on the object.

2. What is “ability”?

Answer: If an object can do work on the outside, we say that the object has energy or energy.

Ask a question

Can electrical energy "do work"? Does electricity have "energy"?

Watch the equipment below and answer the questions above.

Electrical energy and electrical power

We are inseparable from electricity almost everywhere in our lives. When we use electricity, we actually use electricity. The utilization of electrical energy is achieved by converting electrical energy into other forms of energy. Please analyze the example shown in Figure 13-1 and fill in the blanks below.

(a) Electrical energy is converted into _______________;

(b) Electrical energy is converted into _______________;

(c) Electrical energy is converted into _______________;

(d) Electrical energy is converted into _______________.

Electric power

Definition: When electrical energy is converted into other forms of energy, we say that electrical work is done.

In the process of converting electrical energy into other forms of energy, how much electrical energy is converted into other forms of energy is how much electrical work is done by the current. Therefore, the amount of electrical energy converted into other forms of energy can be measured by the amount of electrical work.

think:

1. The small bulb of an ordinary flashlight consumes about 1 J of electric energy per second. It can be said that the current does ______ electrical work;

2. When an electric locomotive travels for 1 minute, it consumes about 100J of electric energy. It can be said that the current has done ______ electrical work.

Calculation of electrical power

Ask the question: What factors are related to the amount of work done by the current?

Make a guess:

For an electric fan, under the same power-on time and the same voltage environment, does it do more work (turn faster) when the current is large or does it do more work when the current is small?

When an electric fan is powered on for the same time and the same current flows through it, does it do more work (turn faster) when the voltage is high or does it do more work when the voltage is low?

An electric fan, under the same current flow and the same voltage environment, does more work when it is powered on for a long time or when it is powered on for a short time?

Conclusion: The amount of work done by the current is directly proportional to the size of the current, the size of the voltage and the length of the energization time.

Electric power calculation formula

Experiments have proven that electrical power can be calculated by the following formula:

1. W=UIt (universally applicable)

2. W=I2Rt

3. W=U²/RT

4. W=Pt (universally applicable)

5. W=UQ (universally applicable)

Example 1: A soldering iron is connected to a 220V circuit, and the current flowing through it is 350mA. How much power does it consume when it is powered for 30 minutes?

Known: U=220V, I=350mA=0.35A, t=1800s.

Asking for: W=?

Solution: From the formula of electric power, we get

W=UIt

=220V×0.35A×1800s

=1.386×105J.

Answer: After energizing for 30 minutes, the electric furnace iron consumes 1.386×105J of electric energy.

Example 2: The dial of an electric energy meter is marked "1200r/(kW·h)", and a certain electrical appliance is connected to the meter alone. After the electrical appliance works for 4 minutes, the energy meter turntable rotates 55r. If the rated voltage of an electrical appliance is 220V, find the current flowing through the electrical appliance.

Solution: The energy meter turntable rotates 55r within 4 minutes, which means that the power consumed by the electrical appliance is:

W =55r/1200r/(kW·h)=55/1200kW·h

=55/1200×3.6×106J=1.65×105J

From W =UIt, the current passing through the electrical appliance is:

I =W/Ut=1.65×105J/220V×240s=3.125A

Answer: The current passing through this electrical appliance is 3.125A

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Update Time: 2024-10-03

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