28. Magnetic Fields and Forces

Which of the following components are typically found in the magnetic system of a magneto?

A 150 V battery is connected across two parallel metal plates of area 28.5 cm² and separation 8.20 mm. A beam of alpha particles (charge +2e, mass 6.64 x 10^-27 kg) is accelerated from rest through a potential difference of 1.75 kV and enters the region between the plates perpendicular to the electric field, as shown in Fig. E27.29. What magnitude and direction of magnetic field are needed so that the alpha particles emerge undeflected from between the plates?

An open plastic soda bottle with an opening diameter of 2.5 cm is placed on a table. A uniform 1.75 T magnetic field directed upward and oriented 25° from vertical encompasses the bottle. What is the total magnetic flux through the plastic of the soda bottle?

How can magnets attract or repel each other without touching?

In the context of Earth's magnetic field, what is one end of a magnetized compass's needle attracted to?

In a typical bar magnet, where is the magnetic force the strongest?

If you bring the $\mathrm{north} \mathrm{pole}$ of one bar magnet close to the $\mathrm{north} \mathrm{pole}$ of another bar magnet, will these magnets be attracted or repelled?

Singly ionized (one electron removed) atoms are accelerated and then passed through a velocity selector consisting of perpendicular electric and magnetic fields. The electric field is 155 V/m and the magnetic field is 0.0315 T. The ions next enter a uniform magnetic field of magnitude 0.0175 T that is oriented perpendicular to their velocity. (a) How fast are the ions moving when they emerge from the velocity selector? (b) If the radius of the path of the ions in the second magnetic field is 17.5 cm, what is their mass?

The Hall effect can be used to measure blood flow speed because the blood contains ions that constitute an electric current. (a) Does the sign of the ions influence the emf? Explain. (b) Determine the flow speed in an artery 3.3 mm in diameter if the measured emf across the width of the artery is 0.13 mV and B is 0.070 T. (In actual practice, an alternating magnetic field is used.)

A bar magnet is placed near the end of a solenoid with its north pole facing the solenoid's south pole. When current flows through the solenoid to create a south magnetic pole at the end closest to the bar magnet, what is the direction of the magnetic force that the solenoid exerts on the bar magnet?