Astudent wants you to demonstrate that an electric current will produce a magnetic field. which set of objects could be used to demostrate this?
a. a battery, a coil of wire and a compass. eliminateb)a compass, some paper clips and a battery.
c. a battery, an iron nail and a long copper wire.
d. an iron nail, a permanent magnet and a battery.

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm