An electromagnet needs a magnetic metal core. To produce a magnetic field, what else is required?

A second metal core?
A solenoid with current or no current running through it? Or a permanent magnet?

Which type of basaltic lava flow has a fairly smooth

Talia is manufacturing rolls of wire for hanging pictures. she needs a material that is so that it can easily be pulled into wire without breaking.

An air-filled capacitor is formed from two long conducting cylindrical shells that are coaxial and have radii of 26 mm and 103 mm. the electric potential of the inner conductor with respect to the outer conductor is - 700 v (k = 1/4πε 0 = 8.99 × 109 n · m2/c2) the energy stored in a 1.0-m length of this capacitor is closest to