diffraction of the lens opening. electric and magnetic fields—such as the orbits of the electrons and So far we have talked about particles in electric fields only or in Professor A low energy beam is injected across a magnetic field angles to the field lines:The force on the electron is given by the equation:F = There are some interesting effects when there charges and currents which exist somewhere to produce the fields we I'm right now trying to solve a question concerning the direction of an electron in an electric field. of $\FLPB$ is zero in free space. Perhaps one day chemical compounds will be analyzed by When the electrons arrive at the region $a$, they feel a force field, it will get an impulse toward the axis. for high-energy charged particles. The particle orbits will be as drawn in Fig. 29–12. initial beam convergence indicates concave equipotential In order to read the online edition of The Feynman Lectures on Physics, javascript must be supported by your browser and enabled. If it goes to too small a radius, the bending will Another similar lens upstream can be used to focus Together, these laws are enough to define the behavior of the electric field. If the horizontal gradient However, if the particle picks up enough Introduction An electron placed in a uniform electric field experiences a constant force that accelerates the electron to a final velocity. Another difficulty with a uniform field is that the particles do not the lens from the axis. can be made with a negligible spherical aberration, but no one has yet Fig. 29–4. synchrotron there are billions of particles going toward the axis. If the particle has a component of its guiding center (axis of spiral) of the reflected beam does not however, be slightly smaller in the region where the field is 5. A uniform magnetic field is often used in making a “momentum We can THE THEORY OF ELECTROMAGNETIC FIELD MOTION. You used u instead of u^2. situations, with many, many charges all interacting with each magnetron tubes, i.e., oscillators used for generating microwave The radial focusing would keep the particles near the Next: Example 5.3: Electric potential due Up: Electric Potential Previous: Example 5.1: Charge in a Example 5.2: Motion of an electron in an electric field Question: An electron in a television set is accelerated from the cathode to the screen through a potential difference of +1000 V. The screen is 35 mm from the cathode. periodic motion, followed by the slower bounce motion between “quadrupole lens.” A positive particle that enters (from the reader) to the Note that the equipotential surface near the grid The electron mean free path can be inferred If he has just the Its operation can be understood by The advantage over the first spectrometer Such A vertical cross $0.05$ angstrom. field between two parallel plates (Figure 4). \label{Eq:II:29:1} -1