🔋college physics i – introduction review

R = mv/qB

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The term 'r = mv/qB' represents the radius of the circular path that a charged particle will follow when moving through a magnetic field. This equation describes the relationship between the particle's momentum, charge, and the strength of the magnetic field, which determines the curvature of the particle's trajectory.

5 Must Know Facts For Your Next Test

  1. The radius of the circular path, 'r', is directly proportional to the particle's momentum, 'm*v', and inversely proportional to the product of the particle's charge, 'q', and the strength of the magnetic field, 'B'.
  2. The equation 'r = mv/qB' is derived from the Lorentz force equation, which describes the force exerted on a charged particle moving through a magnetic field.
  3. The radius of the circular path is an important parameter in the design and operation of various particle accelerators, such as cyclotrons and synchrotrons, which use magnetic fields to control the motion of charged particles.
  4. The term 'r = mv/qB' is also used to determine the energy of a charged particle in a magnetic field, as the particle's kinetic energy is directly related to its momentum.
  5. Understanding the relationship between the particle's radius, momentum, charge, and the magnetic field strength is crucial for analyzing and predicting the behavior of charged particles in various applications, such as mass spectrometry and charged particle beam diagnostics.

Review Questions

  • Explain the physical meaning of the equation 'r = mv/qB' and how it relates to the motion of a charged particle in a magnetic field.
    • The equation 'r = mv/qB' describes the radius of the circular path that a charged particle will follow when moving through a magnetic field. The radius is directly proportional to the particle's momentum (m*v) and inversely proportional to the product of the particle's charge (q) and the strength of the magnetic field (B). This relationship is derived from the Lorentz force equation, which states that a charged particle moving through a magnetic field experiences a force that causes it to follow a curved trajectory. The radius of this circular path is a crucial parameter in the design and operation of particle accelerators, as it determines the energy and trajectory of the charged particles within the system.
  • Describe how the term 'r = mv/qB' can be used to analyze the behavior of charged particles in various applications, such as mass spectrometry and charged particle beam diagnostics.
    • The equation 'r = mv/qB' is widely used in the analysis and understanding of charged particle behavior in various applications, such as mass spectrometry and charged particle beam diagnostics. In mass spectrometry, the radius of the circular path followed by charged particles in a magnetic field is used to determine the mass-to-charge ratio of the particles, which is a fundamental property used for identification and analysis of chemical species. Similarly, in charged particle beam diagnostics, the 'r = mv/qB' equation is used to measure the energy and momentum of the particles within the beam, as well as to analyze the beam's spatial distribution and emittance, which are critical parameters for the optimization and control of particle accelerators and other charged particle-based systems.
  • Explain how the understanding of the relationship between a charged particle's radius, momentum, charge, and the magnetic field strength, as described by the equation 'r = mv/qB', can contribute to the design and operation of particle accelerators, such as cyclotrons and synchrotrons.
    • The equation 'r = mv/qB' is fundamental to the design and operation of particle accelerators, such as cyclotrons and synchrotrons, which use magnetic fields to control the motion of charged particles. The radius of the circular path followed by the particles is a critical parameter, as it determines the size and configuration of the accelerator, as well as the energy and momentum of the particles. By understanding the relationship between the particle's radius, momentum, charge, and the magnetic field strength, as described by the 'r = mv/qB' equation, accelerator designers can optimize the system to achieve the desired particle energies and beam characteristics. This knowledge is used to select the appropriate magnetic field strength, particle charge, and other parameters to ensure the efficient and reliable operation of the accelerator, which is essential for a wide range of scientific and technological applications.