A bar magnet is held near the electron beam in an...

A bar magnet is held near the electron beam in an oscilloscope. The beam passes directly below the south pole of the magnet. In what direction will the beam move on the screen? (Don't try this with a color TV tube. There is a metal mask just behind the screen that separates the pixels for red, green, and blue. If you succeed in magnetizing the mask, the picture will be permanently distorted.)

Key Concepts

Magnetic Fields

Magnetic fields exert force on moving charges and are characterized by their strength and direction. The field lines around a magnet exit from the north pole and enter the south pole. Understanding the orientation and distribution of these fields is crucial for analyzing how charged particles will be deflected when they move through regions where these fields are present.

Deflection of Charged Particles

Charged particles, such as electrons, are deflected by magnetic fields according to the Lorentz force law. The interplay between the particle's velocity and the magnetic field’s direction leads to a curved trajectory. This behavior is essential for understanding electronic devices like cathode ray tubes and oscilloscopes, where precise beam control is required to generate accurate displays.

Lorentz Force

This is the fundamental force acting on a charged particle moving in a magnetic field. It is given by the vector equation F = q(v × B) and determines the magnitude and direction of the force exerted on the particle. In problems involving moving charges in a magnetic field, this force causes the particle to deflect, and understanding its behavior is critical to analyzing the resulting motion.

Right-Hand Rule

The right-hand rule is a mnemonic used to determine the direction of the force experienced by a positive charge moving in a magnetic field, following the cross product in the Lorentz force equation. Although electrons carry a negative charge (which reverses the direction of the force), the rule is still fundamental in visualizing how moving charges interact with magnetic fields in three-dimensional space.

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