"Thermal Effect of Electric Current" Electric Work and Electric Power PPT Courseware 2

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"Thermal Effect of Electric Current" Electric Work and Electric Power PPT Courseware 2

Explore: What factors are related to the heat generated by electric current passing through an electric heater?

in conclusion

① Resistor R

②Current I

③Power-on time t

Use your brain

You can control other variables unchanged, first study the relationship between the heat emitted by the electric heater and the resistance R, then study its relationship with the current I, and finally study its relationship with the power-on time t.

The relationship between heat and resistance

The experiment found that the matchstick in _______ was ignited first.

Conclusion: When the current and power-on time are the same, the resistor with a resistance of ____ generates more heat.

The relationship between heat and current

Experiment find-outs:

The matchstick ignited quickly under the current ____.

Conclusion: When the resistance and energization time are the same, the resistance with current ____ generates more heat.

The relationship between heat and time

Conclusion: When the resistance and current are the same, the resistor with the energization time of _____ generates more heat.

2. Expression of heat generated by electric current

1. Joule’s law

The heat generated when current flows through a conductor is proportional to the square of the current, the resistance of the conductor, and the time it takes to energize.

2. Formula: Q=I2Rt

Unit: Q--joule I--ampere R--ohm t--second

Application of electric heating

1. Electric heater:

A device that uses electric current to perform work and convert ____ energy into ____ energy.

2. Principle of electric heater:

A heating device made of _______ that uses electric current.

The main component of an electric heater is _______. It is determined by resistivity _____. Heating equipment made of alloy wire with a melting point of ____.

[Exercise 1]: The resistance of a certain electric heater resistance wire is 2 ohms. When a current of 1 A passes through, how many joules of heat are generated in 1 minute?

Solution: Q= I2Rt=(1A)2 × 2Ω × 60S=120J

[Exercise 2]: In order to study the effect of temperature on seed germination, the extracurricular activity group is going to make an electric oven, which is required to generate 6×104J of heat in 10 minutes. It is connected to a household circuit. Please calculate the electric heating of this electric oven. What is the resistance of the wire?

[Exercise 3]: When an incandescent lamp marked "220V 100W" works normally, how much heat will it generate in 1 minute? How much power will it consume? What if it is connected to a 55V circuit?

[Exercise 4]: The ratio of the resistances of the two electric heaters is 4.3. When the same current is passed, the ratio of the heat generated in the same time is _____; if the resistances of the two electric heaters are the same, the intensity of the passing current is 1�3, the ratio of heat generated in equal time is ______.

think about it

1. The light bulb and the wire are connected in series in the circuit. The current is the same. The light bulb is so hot that it glows, but the wire is not very hot. Why is this?

2. If the light bulb is replaced by a high-power electric stove with the same wire, the wire will heat up significantly and even burn the wire. Why is this?

As shown in the figure, the power supply voltage is 220 volts. R is the soldering iron, marked with "220V, 40W"; L is the light bulb, marked with "PZ220-40". When switch S is closed, the heat generated by the soldering iron per minute It is ______ joules. When switch S is turned off, the actual power of the soldering iron is __ watts; after switch S is turned off, the entire circuit consumes 1 kilowatt of electricity for __ hours.

The picture is a simplified circuit diagram of an electric blanket. The power supply voltage is 220V. R1 is a heating resistor, R2 is a voltage dividing resistor with a resistance of 616Ω, and S is a switch that controls the working status of the electric blanket. When S goes to contact 1, it is in the off state; when S goes to contact 2, it is in the low temperature state; when S goes to contact 3, it is in the high temperature state. At this time, the power is 100W. Find: (l) When switch S is turned to contact 3. What is the heating resistance R1 of the electric blanket? (2) When switch S is turned to contact 2, how much current flows through the circuit? How many watts does the heating resistor R1 consume?

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Update Time: 2024-10-18

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