Magnetic Forces, Field Strength, and Magnetic Field Lines

All flashcards

What equation gives the magnetic force on a moving charge?

$\vec{F}=q\vec{v}\times\vec{B}$; the force is perpendicular to both velocity and magnetic field.

How is magnetic force magnitude calculated?

$F=|q|vB\sin\theta$, where $\theta$ is the angle between velocity and magnetic field.

How does the right-hand rule determine magnetic-force direction?

For a positive charge, point fingers along velocity and curl toward the field; the thumb gives force direction.

What do magnetic field-line direction and spacing represent?

The tangent gives field direction; closer spacing indicates greater field strength.

How are teslas and gauss related?

$1\,\mathrm{G}=10^{-4}\,\mathrm{T}$; the tesla is the SI unit of magnetic-field strength.

Quiz questions

1. A positive charge moves along the positive $x$-axis while the magnetic field points along the positive $z$-axis. Which direction is the magnetic force?Answer: Along the negative $y$-axis.
2. When using the right-hand rule to find the force direction on a negative charge, what adjustment is needed?Answer: Reverse the direction found for a positive charge.
3. What does close spacing between magnetic field lines indicate?Answer: A stronger magnetic field.
4. Why can two magnetic field lines not cross?Answer: The magnetic field has only one direction at each point.
5. Outside a bar magnet, in which direction do magnetic field lines run?Answer: From the north pole toward the south pole.