A circuit consists of two wires made of iron andcopper, respectively, connected in series as shown below. If the electric field strength is required to be the same in both wires, and the copper wire has a radius of 2.0 mm, determine the radius of the iron wire.

• A. 3.0 mm
• B. 4.5 mm
• C. 6.0 mm
• D. 7.5 mm

Answer: (B)