An air-filled capacitor consists of two parallel plates, each with an area of 10.0 cm2, separated by a distanceof 2.00 mm. A 20.0-V potential difference isapplied to these plates. Calculate (a) the electric fieldbetween the plates, (b) the surface charge density,(c) the capacitance, and (d) the charge on each plate.

Electromagnetic induction. a coil of wire contains n turns and has an electrical resistance r. the radius of each turn is a. initially, inside the coil there exists a uniform magnetic field of magnitude b0 parallel to the axis of the coil. the magnetic field is then reduced slowly. the current induced in the coil is i. how long does it take for the magnitude of the uniform field to drop to zero?