About

A Velocity Selector

A velocity selector is a region in which there is a uniform electric field and a uniform magnetic field. The fields are perpendicular to one another, and perpendicular to the initial velocity of the charged particles that are passing through the region.

The force exerted on a charged particle by the electric field is given by:

F = qE

The magnitude of the force exerted by the magnetic field is F = qvB, as long as the velocity is perpendicular to the field.

The idea is that, if the two forces are equal and opposite, the net force is zero, and the particle passes through the region without changing direction. With the magnetic force being speed dependent, however, any charges traveling faster or slower than the ones that go straight through will be deflected one way or another out of the beam. You can investigate these concepts with this simulation.

In this simulation, the electric field is directed in the z-direction (upward/ downward which is represented by the red arrow) and the magnetic field is directed in the y-direction (into the plane/ out of the plane of the screen which is represented by the orange arrow).

Note also that when the charged particle is inside the region, the force acting on the charged particle will be shown acting on the particle. The arrow in green represents the electric force and the arrow in cyan represents the magnetic force.

 

Translations

Code	Language		Translator	Run

Credits

Fu-Kwun Hwang; lookang; Chee Wah Ong

Sample Learning Goals

Briefing Document: Velocity Selector Simulation

1. Introduction:

This document provides a review of the "Velocity Selector Electric and Magnetic Force JavaScript HTML5 Applet Simulation Model" resource from Open Educational Resources / Open Source Physics @ Singapore. The primary focus is on understanding the core concepts and functionality of this simulation tool within the context of physics education. The document analyzes the purpose, key principles, and learning opportunities offered by this interactive resource.

2. Main Theme: Velocity Selector and Electromagnetic Forces

The central theme is the concept of a velocity selector, a device that uses perpendicular electric and magnetic fields to isolate charged particles with a specific velocity. This tool demonstrates the interplay of electric and magnetic forces on a charged particle.

3. Key Concepts and Principles:

• Velocity Selector Definition: A velocity selector is defined as a region containing a uniform electric field and a uniform magnetic field that are perpendicular to each other and also perpendicular to the initial velocity of the charged particles passing through it.

"A velocity selector is a region in which there is a uniform electric field and a uniform magnetic field. The fields are perpendicular to one another, and perpendicular to the initial velocity of the charged particles that are passing through the region."

• Electric Force: The electric force on a charged particle is directly proportional to the charge (q) and the electric field strength (E), represented by the equation F = qE.
• "The force exerted on a charged particle by the electric field is given by: F = qE"
• Magnetic Force: The magnetic force on a charged particle is proportional to the charge (q), the velocity of the particle (v), and the magnetic field strength (B), given by F = qvB, provided the velocity is perpendicular to the field.
• "The magnitude of the force exerted by the magnetic field is F = qvB, as long as the velocity is perpendicular to the field."
• Force Balance and Velocity Selection: The core idea is that when the electric and magnetic forces are equal in magnitude and opposite in direction, they cancel each other out resulting in zero net force. This allows only particles with a specific velocity to pass straight through the velocity selector without deflection. The specific velocity is determined by the equation E = vB or v = E/B.
• "The idea is that, if the two forces are equal and opposite, the net force is zero, and the particle passes through the region without changing direction."
• Speed Dependency of Magnetic Force: Because the magnetic force is speed-dependent (F=qvB), particles moving faster or slower than the selected velocity will be deflected out of the beam.
• "With the magnetic force being speed dependent, however, any charges traveling faster or slower than the ones that go straight through will be deflected one way or another out of the beam."

4. Simulation Details

• Visualization: The simulation provides a visual representation of the forces involved, using arrows to show the directions and relative magnitudes of:
• Electric field: Represented by red arrow pointing up or down.
• Magnetic field: Represented by an orange arrow pointing into or out of the plane.
• Electric force: Represented by a green arrow.
• Magnetic force: Represented by a cyan arrow.
• Interactive Exploration: Users can manipulate parameters in the simulation to observe how changes in particle velocity, electric field, and magnetic field affect the trajectory of the charged particles. This enables a hands on experience in understanding the concepts.

5. Educational Value and Learning Goals:

• Conceptual Understanding: The simulation allows users to visualize the relationship between electric and magnetic fields, the forces they exert on charged particles, and the concept of force balance.
• Inquiry-Based Learning: The interactive nature of the tool encourages inquiry-based learning. Students can investigate the effects of varying parameters and discover the principles of a velocity selector through experimentation.
• Engagement: By visualizing forces and particle trajectories, the simulation engages students and makes abstract physics concepts more tangible and easier to grasp.

6. Contextualization within OER Platform:

• Part of a Broader Resource: This velocity selector simulation is one of many interactive tools on the Open Educational Resources / Open Source Physics @ Singapore platform. The list of related resources demonstrates the platform's wide range of physics simulations, including electromagnetism, mechanics, and more.
• Open Source and Adaptable: The resources are designed to be embeddable into other web pages. The platform promotes open access and community-driven educational resources which makes them freely available for educators to integrate into their teaching methods.

7. Conclusion:

The Velocity Selector JavaScript HTML5 Applet Simulation Model is a valuable tool for educators teaching electromagnetism. Its interactive features, coupled with a clear representation of forces, provide students with a strong foundation for understanding the fundamental concepts of a velocity selector. The availability of this and similar resources within the open educational platform fosters accessible, inquiry-based learning for students.

For Teachers

Velocity Selector Study Guide

Quiz

1. What is a velocity selector?
2. How are the electric and magnetic fields oriented in a velocity selector?
3. What is the formula for the electric force on a charged particle?
4. What is the formula for the magnetic force on a charged particle, when velocity is perpendicular to the field?
5. How do the electric and magnetic forces compare for a particle that passes straight through the selector without deflection?
6. Why do particles moving faster or slower than the "selected" speed get deflected in a velocity selector?
7. In this simulation, which direction is the electric field?
8. In this simulation, which direction is the magnetic field?
9. What do the green and cyan arrows represent in the simulation?
10. What is the purpose of the simulation itself?

Quiz Answer Key

1. A velocity selector is a region with a uniform electric field and a uniform magnetic field, where the fields are perpendicular to each other and to the velocity of charged particles entering the region.
2. The electric and magnetic fields are perpendicular to each other and also perpendicular to the initial velocity of the charged particles passing through.
3. The formula for the electric force on a charged particle is F = qE, where q is the charge and E is the electric field strength.
4. The magnitude of the magnetic force when the velocity is perpendicular to the field is F = qvB, where q is the charge, v is the velocity, and B is the magnetic field strength.
5. For a particle to pass straight through without deflection, the electric and magnetic forces must be equal in magnitude and opposite in direction, resulting in a net force of zero.
6. Because the magnetic force is speed dependent, faster particles experience a greater magnetic force and slower particles experience less, so their paths are bent accordingly.
7. In this simulation, the electric field is directed in the z-direction, which can be interpreted as upward or downward.
8. In this simulation, the magnetic field is directed in the y-direction, which can be interpreted as into or out of the plane of the screen.
9. The green arrow represents the electric force acting on the charged particle, and the cyan arrow represents the magnetic force.
10. The purpose of the simulation is to allow users to investigate the concepts of electric and magnetic forces acting on charged particles in a velocity selector and the impact of changing parameters.

Essay Questions

1. Explain the underlying physics principles that govern the operation of a velocity selector. Include a discussion of how electric and magnetic forces interact to achieve velocity selection.
2. Discuss the implications of the velocity selector's speed dependence on magnetic force. What are the limitations and real-world applications that can be associated with that.
3. How can a simulation model like the one described in the source enhance understanding of complex physics concepts compared to traditional methods? Consider the learning advantages of visual and interactive elements.
4. Describe a scenario where you could use a velocity selector. Explain the experimental setup, the rationale behind using the velocity selector, and the desired outcome.
5. How could the simulation be further improved? Consider elements such as greater controls, different visualization styles, or additional features that could be added.

Glossary

Velocity Selector: A device or region where perpendicular electric and magnetic fields are used to select particles of a specific velocity.

Electric Field: A region where an electric charge experiences a force, measured in Newtons per Coulomb (N/C).

Magnetic Field: A region where a moving electric charge experiences a force, measured in Tesla (T).

Electric Force: The force exerted on a charged particle by an electric field, calculated as F = qE.

Magnetic Force: The force exerted on a moving charged particle by a magnetic field, calculated as F = qvB when velocity is perpendicular to the field.

Charge (q): A fundamental property of matter that can be positive or negative and is measured in Coulombs (C).

Velocity (v): The speed and direction of motion of an object, measured in meters per second (m/s).

Deflection: The change in the direction of travel of a particle due to a force.

Net Force: The overall force acting on an object, found by adding all forces acting on it as vectors.

Research

[text]

Video

[text]

 Version:

Other Resources

[text]

Frequently Asked Questions: Velocity Selectors and Related Concepts

1. What is a velocity selector and how does it work? A velocity selector is a region with both a uniform electric field and a uniform magnetic field, oriented perpendicular to each other and to the path of charged particles entering the region. The electric field exerts a force on the charged particles in one direction, while the magnetic field exerts a force in the opposite direction. When the magnitudes of these two forces are equal, the net force on the particle is zero, and it passes through the selector without being deflected.
2. How are the electric and magnetic fields oriented within a velocity selector? In the example provided by the simulation, the electric field is directed along the z-axis (up or down), represented by the red arrow, and the magnetic field is directed along the y-axis (into or out of the screen), represented by the orange arrow. Crucially, both fields are perpendicular to each other and also perpendicular to the direction of motion of the charged particles initially traveling through the region.
3. What are the forces acting on a charged particle within the velocity selector? Two forces act on a charged particle within a velocity selector. The electric field exerts a force F = qE, where q is the charge of the particle, and E is the electric field strength. The magnetic field exerts a force F = qvB, where v is the velocity of the particle, and B is the magnetic field strength. These forces are vector quantities that point in opposing directions. The direction of the magnetic force is determined by the right-hand rule, where the fingers point in the direction of the velocity, and the palm points in the direction of the magnetic force (when the charge is positive).
4. How does the velocity of a particle affect its path within the velocity selector? Only particles moving at a specific speed where the electric and magnetic forces are balanced will pass through the velocity selector undeflected. If a particle is moving too slowly, the electric force will be greater, and the particle will be deflected in the direction of the electric force. Conversely, if a particle is moving too quickly, the magnetic force will dominate, and the particle will be deflected in the direction of the magnetic force. Because the magnetic force depends on speed, the speed is the primary factor that determines whether or not the forces will be balanced and the particle will not be deflected.
5. What do the green and cyan arrows in the simulation represent? The green arrow represents the electric force acting on a charged particle, and the cyan arrow represents the magnetic force. These arrows change size and direction to reflect how the forces are changing within the velocity selector. They can be observed in the simulation as visual aids for students learning these concepts.
6. How does the provided simulation help in understanding velocity selectors? The simulation allows users to visually and interactively explore how electric and magnetic fields affect charged particles. By changing parameters such as field strength and particle velocity, students can directly see how these changes impact the path of the particles. It provides a dynamic model of the concept and is a useful tool for both learning about velocity selectors and investigating different particle behavior under varied conditions.
7. What is Open Source Physics @ Singapore and how does it relate to the simulation? Open Source Physics @ Singapore is an initiative that promotes the use of open-source resources for physics education. They create and share interactive simulations like the velocity selector model, providing tools for teachers and students to explore physical concepts in an engaging way. This organization is committed to making these resources publicly available.
8. What other resources are associated with Open Source Physics @ Singapore? Open Source Physics @ Singapore has numerous resources and tools, many of which are listed on the page associated with the velocity selector simulation. These include simulations for various topics, such as wave phenomena, electromagnetism, mechanics, math, and more. They offer models that cover a wide array of subjects and utilize different software including JavaScript and HTML5. They also list workshops and learning events for teachers, which makes it a comprehensive education resource.