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A magnetic field can force a charged particle to move in a circular path. Suppose that an electron moving in a circle experiences a radial acceleration of magnitude \(3.0 \times 10^{14} \mathrm{~m} / \mathrm{s}^{2}\) in a particular magnetic field. (a) What is the speed of the electron if the radius of its circular path is \(15 \mathrm{~cm} ?\) (b) What is the period of the motion?

Short Answer

Expert verified
(a) Speed: \(6.7 \times 10^6\, \mathrm{m/s}\); (b) Period: \(1.4 \times 10^{-7}\, \mathrm{s}\).

Step by step solution

01

Understand the Centripetal Acceleration Formula

A charged particle moving in a circular path due to a magnetic field experiences a centripetal acceleration, which is given by the formula \[ a = \frac{v^2}{r} \]where \( a \) is the radial or centripetal acceleration, \( v \) is the speed of the particle, and \( r \) is the radius of the circular path. We are given \( a = 3.0 \times 10^{14} \ \mathrm{m/s^2} \) and \( r = 15 \ \mathrm{cm} = 0.15 \ \mathrm{m} \).
02

Solve for the Speed of the Electron

To find the speed \( v \) of the electron, rearrange the centripetal acceleration formula to solve for \( v \):\[ v = \sqrt{a \cdot r} \]Substitute the given values into this formula:\[ v = \sqrt{3.0 \times 10^{14} \ \mathrm{m/s^2} \times 0.15 \ \mathrm{m}} \]Calculating this gives:\[ v \approx \sqrt{4.5 \times 10^{13}} \approx 6.7 \times 10^6 \ \mathrm{m/s} \]
03

Understand the Period of Motion Formula

The period \( T \) of motion, which is the time it takes to complete one full circle, is given by the formula:\[ T = \frac{2\pi r}{v} \]with \( r = 0.15 \ \mathrm{m} \) and \( v = 6.7 \times 10^6 \ \mathrm{m/s} \).
04

Calculate the Period of the Electron's Motion

Substitute the known values into the period formula:\[ T = \frac{2\pi \times 0.15 \ \mathrm{m}}{6.7 \times 10^6 \ \mathrm{m/s}} \]This gives:\[ T = \frac{0.3\pi}{6.7 \times 10^6} \approx 1.4 \times 10^{-7} \ \mathrm{s} \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Centripetal Acceleration
Centripetal acceleration is a key concept when discussing the motion of a charged particle in a magnetic field. It refers to the acceleration that acts on an object moving in a circular path, directed towards the center of the circle. This is what keeps the object in that path.
A charged particle, like an electron, experiences this centripetal acceleration due to the presence of a magnetic field. In mathematical terms, the centripetal acceleration \( a \) can be found using the formula: \[ a = \frac{v^2}{r} \] where \( v \) is the speed of the object and \( r \) is the radius of the circular path. In the context of electron motion, knowing the centripetal acceleration allows us to determine the speed required for an electron to maintain its prescribed circular path, given a certain radius.
  • Centripetal acceleration keeps the particle on a curved path.
  • It's always directed towards the center of the circle.
  • It's crucial for understanding particle dynamics in magnetic fields.
Electron Motion
The motion of an electron in a magnetic field is an illustrative example of how electromagnetic forces affect charged particles. Electrons, being negatively charged, respond to magnetic fields with a force that is central to their motion, causing them to trace a curved path.
This motion is defined by the Lorentz force, which is perpendicular to both the velocity of the electron and the magnetic field direction. The result is a circular or spiral trajectory depending on the component of the electron's velocity that is perpendicular to the magnetic field. Because they are so light, electrons can be made to undergo circular motion in small, uniform magnetic fields quite easily. Calculating their speed in such scenarios involves using the concept of centripetal acceleration, which ensures that their path remains circular.
This is an essential property used in various technologies, like electron beams in cathode-ray tubes and for examining atomic structures in particle physics.
Period of Motion
The period of motion refers to the time it takes for a charged particle to complete one full cycle along its circular path. It is an important aspect of understanding the dynamics of motion in magnetic fields.
The period \( T \) is calculated using the formula: \[ T = \frac{2\pi r}{v} \] where \( r \) is the radius of the motion and \( v \) is the speed of the particle. This formula shows that the period is directly proportional to the path length (circumference of the circle) and inversely proportional to the particle's speed.Understanding and calculating the period can help determine how often the particle performs its circular motion, which is crucial in applications like cyclotrons that accelerate particles to high speeds.
  • The period helps in determining the frequency of motion.
  • It assists in predicting future positions of the electron in its path.
  • Vital for synchronizing systems using charged particles.
Circular Path
A circular path in the context of a charged particle in a magnetic field refers to the trajectory that the particle follows as it experiences a perpendicular magnetic force. This path is a result of the centripetal force provided by the magnetic field's effect on the particle’s charge.
The radius of this circular path is an important parameter, calculated using the balance between magnetic force and its resulting centripetal acceleration.The radius \( r \) is crucial as it defines the extent of the circular path and is used in calculating other properties, such as the speed of the particle or the period of its motion. In electron applications, knowing the radius enables designing equipment that precisely guides electron beams for tasks involving microscopic dimensions, enhancing precision in electronics and microscopy.
Charged Particle
A charged particle is any particle that possesses an electric charge, either positive or negative. In the study of electromagnetic fields, understanding the behavior of charged particles, such as electrons, is fundamental.
The motion of a charged particle under the influence of a magnetic field is governed by the interaction between the particle's charge and the magnetic forces. In practical applications, charged particles are manipulated using magnetic fields in various ways:
  • In particle accelerators, charged particles are sped up to high velocities.
  • In magnetic containment, they are used to study plasma and fusion.
  • Charged particles' paths are utilized in devices like mass spectrometers.
Understanding these interactions allows engineers and scientists to devise means to control and exploit particle motion for research and technology, from nuclear physics to medical imaging.

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