Lesson Plan | Traditional Methodology | Electricity: Electric Power

Objectives

Duration: 10 - 15 minutes

The purpose of this stage is to introduce students to the topic of electric power, highlighting its importance and practical application. This stage aims to ensure that students understand the fundamental concepts and are prepared to apply this knowledge in solving specific problems related to electric power and resistance heating.

Main Objectives

1. Explain the concept of electric power and how it relates to energy and time.

2. Demonstrate the calculation of power generated by Joule effect in a resistor or circuit.

3. Solve practical problems involving the calculation of power and the time needed for a resistor to heat a certain amount of water.

Introduction

Duration: 10 - 15 minutes

 The purpose of this stage is to introduce students to the topic of electric power, emphasizing its importance and practical application. This stage aims to ensure that students understand the fundamental concepts and are prepared to apply this knowledge in solving specific problems related to electric power and resistance heating.

Context

 To start the lesson on electric power, it is important to contextualize the theme in the daily lives of students. Electric power is a fundamental concept not only in Physics but also in everyday life. For example, when we use household appliances like microwaves, electric showers, or computers, we are constantly dealing with electric power. These devices are designed to operate efficiently, converting electrical energy into other forms of energy, such as thermal or luminous, according to their specificities.

Curiosities

 Curiosity: Did you know that an electric shower, during a shower, consumes an amount of energy that could keep a light bulb on for several hours? The electric power of a shower can reach up to 7500 watts (W), which is much more than most household appliances. This shows the importance of understanding electric power to better manage energy consumption in our homes.

Development

Duration: 45 - 50 minutes

 The purpose of this stage is to deepen students' understanding of the concept of electric power, reinforcing theory with practical examples and problem-solving. By the end of this section, students should be able to apply the formulas of electric power in different contexts and solve complex problems involving calculations of energy, voltage, current, and resistance.

Covered Topics

1.  Definition of Electric Power: Explain that electric power is the amount of electrical energy converted into another form of energy (such as heat, light, etc.) per unit of time. The basic formula is P = E/t, where P is power (in watts), E is energy (in joules), and t is time (in seconds). 2.  Relationship between Power, Voltage, and Current: Detail the relationship P = V * I, where P is power in watts, V is voltage in volts, and I is current in amperes. Explain how this formula is derived from the combination of Ohm's laws and the definition of power. 3. ️ Joule Effect and Heating: Explain the Joule effect, which is the heating of an electrical conductor due to current flow. The formula P = I² * R should be highlighted, where R is the resistance of the material in ohms. Discuss practical applications, such as the operation of heaters and electric showers. 4.  Practical Calculations: Demonstrate how to calculate electric power in different contexts, such as in simple circuits and household appliances. Provide clear examples, such as calculating the power of a light bulb or an electric heater. 5.  Everyday Applications: Discuss the importance of understanding electric power for conscious energy consumption. Exemplify with the calculation of energy consumption of household appliances and the reading of electricity bills.

Classroom Questions

1. 1. An electric shower has a resistance of 10 ohms and is powered by a voltage of 220 V. What is the power dissipated by the shower? 2. 2. Calculate the energy consumed by a 60 W light bulb that stays on for 5 hours. 3. 3. An electric heater of 1500 W is used to heat 2 liters of water. Assuming all the energy from the heater is used to heat the water, how much time will be necessary to increase the temperature of the water by 40°C? (Consider the specific heat of water as 4.186 J/g°C)

Questions Discussion

Duration: 20 - 25 minutes

 The purpose of this stage is to review and consolidate the knowledge acquired by students during the lesson. By discussing the questions and engaging students in reflections, it seeks to ensure that they understand not only the theory but also the practical applications and the impact of electric power in their daily lives.

Discussion

•  Question 1: An electric shower has a resistance of 10 ohms and is powered by a voltage of 220 V. What is the power dissipated by the shower?

Detailed Explanation: To solve this question, we use the formula for electric power in terms of voltage and resistance: P = V² / R. Substituting the provided values, we have P = (220)² / 10 = 4840 W. Therefore, the power dissipated by the shower is 4840 watts.

•  Question 2: Calculate the energy consumed by a 60 W light bulb that stays on for 5 hours.

Detailed Explanation: To calculate the energy consumed, we use the formula E = P * t, where E is energy in joules, P is power in watts, and t is time in seconds. First, we convert the time to seconds: 5 hours = 5 * 3600 = 18000 seconds. Then, E = 60 W * 18000 s = 1080000 J (or 1.08 MJ). The energy consumed by the light bulb is 1.08 megajoules.

•  Question 3: An electric heater of 1500 W is used to heat 2 liters of water. Assuming all the energy from the heater is used to heat the water, how much time will be necessary to increase the temperature of the water by 40°C? (Consider the specific heat of water as 4.186 J/g°C)

Detailed Explanation: To solve this question, we use the formula Q = mcΔT, where Q is the amount of heat, m is the mass of the water, c is the specific heat, and ΔT is the temperature change. First, we convert the volume of water to mass, knowing that the density of water is 1 g/cm³: 2 liters = 2000 g. Then, Q = 2000 g * 4.186 J/g°C * 40°C = 334880 J. Knowing that the power of the heater is 1500 W, which is equivalent to 1500 J/s, the time t required is Q / P = 334880 J / 1500 J/s ≈ 223.25 s, or approximately 3.72 minutes.

Student Engagement

1. ❓ Question 1: How can the power of an electrical device influence the monthly electricity bill of a household? 2. ❓ Question 2: What are the ways to minimize electricity consumption at home without compromising comfort? 3. ❓ Reflection: Consider a scenario where you need to choose between two appliances with different powers but the same function. What factors would you take into account in your decision besides electric power?

Conclusion

Duration: 10 - 15 minutes

The purpose of this stage is to review and consolidate the knowledge acquired during the lesson, reinforcing the main concepts and ensuring that students understand the practical relevance of what was taught. This final review helps to fix the content and clarify any remaining doubts.

Summary

• Electric power is the amount of energy converted into another form per unit of time, with the formula P = E/t.
• The relationship between power, voltage, and current is given by P = V * I.
• The Joule effect is the heating of a conductor due to current flow, described by the formula P = I² * R.
• Practical calculations of electric power in circuits and household appliances were demonstrated.
• The importance of conscious energy consumption was discussed with practical examples.

The lesson connected theory with practice by demonstrating calculations of electric power in everyday contexts, such as the use of household appliances. Practical examples and problem-solving helped understand how theoretical concepts apply in real situations, facilitating students' assimilation.

Understanding electric power is crucial for effective energy consumption management at home and in industry. Electric power directly impacts electricity bills and sustainability. Knowledge on how to calculate and optimize the use of electrical energy is essential for conscious and responsible consumption.