Exploring Magnetic Force: Theory and Practice

Objectives

1. Understand the definition and characteristics of the magnetic force on moving electric charges.

2. Calculate the magnitude and direction of the magnetic force on a charge moving in a magnetic field.

3. Explore the relationship between the speed of the charge, the strength of the magnetic field, and the resulting force.

4. Understand the perpendicular orientation of the magnetic force in relation to the speed of the charge and the magnetic field.

Contextualization

The magnetic force on electric charges is a fundamental phenomenon with various practical applications in our daily lives. For example, electric motors used in appliances operate thanks to the magnetic force. Technologies such as magnetic resonance imaging in hospitals and magnetic levitation trains (Maglev) also depend on this principle. In this lesson, we will explore how the magnetic force acts on moving charges, a central concept for the development of many modern technologies.

Relevance of the Theme

Knowledge about the magnetic force on electric charges is vital in the current context, as it is present in various technologies and industrial sectors. Understanding this subject is essential for careers in engineering, information technology, and healthcare, as well as being fundamental for innovation and technological development.

Magnetic Force on Moving Electric Charges

The magnetic force is exerted on an electric charge moving in a magnetic field. This force is perpendicular both to the direction of the charge's velocity and to the direction of the magnetic field, and its magnitude can be calculated using the formula F = qvBsin(θ), where F is the magnetic force, q is the electric charge, v is the velocity of the charge, B is the strength of the magnetic field, and θ is the angle between the charge's velocity and the magnetic field.

• The magnetic force acts perpendicular to the charge's velocity and the magnetic field.

• The magnitude of the force can be calculated using the formula F = qvBsin(θ).

• The magnetic force is maximized when the charge's velocity is perpendicular to the magnetic field (θ = 90°).

Right-Hand Rule

The right-hand rule is a practical tool used to determine the direction of the magnetic force on a moving charge. To apply the rule, point your thumb in the direction of the charge's velocity (v), your fingers in the direction of the magnetic field (B), and your palm will indicate the direction of the magnetic force (F) for a positive charge.

• The right-hand rule helps visualize the direction of the magnetic force.

• The thumb represents the direction of the charge's velocity.

• The fingers represent the direction of the magnetic field.

• The palm indicates the direction of the magnetic force for a positive charge.

Relationship Between Speed, Magnetic Field, and Force

The magnetic force depends on the speed of the charge, the strength of the magnetic field, and the orientation between them. The force is directly proportional to the speed of the charge and the strength of the magnetic field, being maximized when the charge moves perpendicular to the field. This relationship is crucial for the operation of devices such as electric motors and Maglev trains.

• The magnetic force increases with the speed of the charge and the strength of the magnetic field.

• The force is maximized when the charge moves perpendicular to the magnetic field.

• This relationship is applied in technologies such as electric motors and Maglev trains.

Practical Applications

• Maglev Trains: Use magnetic force to float and move quickly without contact with the tracks, providing efficient and silent transportation.
• Electric Motors: The magnetic force is fundamental to the operation of electric motors, which are used in a wide range of devices, from household appliances to electric vehicles.
• Magnetic Resonance: Used in medical diagnostics, magnetic resonance imaging leverages the magnetic force to generate detailed images of the inside of the human body.

Key Terms

• Magnetic Force: The force exerted on a moving electric charge in a magnetic field.

• Right-Hand Rule: A method to determine the direction of the magnetic force on a moving charge.

• Magnetic Field: A region of space where magnetic forces can be observed, usually generated by magnets or electric currents.

• Electric Charge: A physical property of particles that causes electromagnetic interaction.

Questions

• How can understanding the magnetic force influence the development of new technologies in the future?

• In what way does the right-hand rule facilitate the understanding of magnetic phenomena?

• What are the challenges and benefits of applying magnetic force in transportation technologies like Maglev trains?

Conclusion

To Reflect

In this lesson, we explored the magnetic force on moving electric charges, a crucial concept for various modern technologies. We saw how the magnetic force acts perpendicular to the charge's velocity and the magnetic field, and how we can calculate its magnitude. Additionally, we discussed the importance of this knowledge for practical applications such as Maglev trains, electric motors, and magnetic resonance imaging. Understanding these principles is not only fundamental for the development of new technologies, but also opens doors for careers in technical and scientific fields.

Mini Challenge - Practical Challenge: Exploring Magnetic Force with a Homopolar Motor

Build a simple homopolar motor to observe the magnetic force in action. This practical challenge will allow you to visualize how the magnetic force acts on a moving charge.

• Gather the necessary materials: a AA battery, a neodymium magnet, a copper wire, and adhesive tape.
• Attach the magnet to the end of the battery using adhesive tape.
• Wrap the copper wire into a spiral shape.
• Connect the ends of the wire to the battery terminals, creating a closed circuit.
• Observe how the copper wire begins to spin, demonstrating the magnetic force in action.