29. Sources of Magnetic Field

Two identical bar magnets are placed parallel to each other with their north poles facing each other at a short distance apart. Which of the following best describes the force between the two magnets?

Suppose you held two point charges, each with charge $q$, moving parallel to each other with velocity $v$ and separated by a distance $r$. Which of the following best describes the magnetic force that one charge exerts on the other?

Which combination of magnetic poles will repel each other when brought close together?

Which of the following best explains why two like poles of magnets repel each other?

As the distance between two magnetic poles ($r$) decreases, how does the magnetic force ($F$) between them change?

Which of the following best explains why the magnetic needle in a compass points toward geographic north?

In what way are magnetic poles very different from electric charges?

What happens to the magnetic force between two moving point charges as the distance between them increases?

When two point charges, each with charge $q$, move parallel to each other with the same velocity $v$ in the same direction, what is the nature of the magnetic force between them?

Two point charges, each with charge $q$, move parallel to each other with velocity $v$ in the same direction and are separated by a distance $r$. Which of the following correctly gives the magnitude of the magnetic force that one charge exerts on the other?

Which statement best describes the general rule about magnetic attraction between two moving point charges?

Two point charges, each with charge $q$, move parallel to each other with velocity $v$ in the same direction and are separated by a distance $r$. Which configuration will produce the strongest magnetic force of attraction between the charges?

When you place the $\mathrm{north}\mathrm{pole}$ of one magnet next to the $\mathrm{north}\mathrm{pole}$ of another magnet, what is the resulting interaction between the two magnets?

Figure E27.49 shows a portion of a silver ribbon with z₁ = 11.8 mm and y₁ = 0.23 mm, carrying a current of 120 A in the +x-direction. The ribbon lies in a uniform magnetic field, in the y-direction, with magnitude 0.95 T. Apply the simplified model of the Hall effect presented in Section 27.9. If there are 5.85 x 10²⁸ free electrons per cubic meter, find (a) the magnitude of the drift velocity of the electrons in the x-direction; (b) the magnitude and direction of the electric field in the z-direction due to the Hall effect; (c) the Hall emf.