Use Ohm's law and wire resistance formula to find diameter

Steps:

• Calculate resistance R = V / I using battery voltage V from diagram and I = 4.0 A.
• Compute cross-sectional area A = ρ L / R with ρ = 6.0 × 10^{-5} Ω m and L = 2.0 m.
• Relate A to diameter via A = π (d/2)^2, so d = 2 √(A / π).
• Substitute values to obtain d = 5.1 × 10^{-2} m.

Why D is correct:

• It satisfies R = ρ L / A where A = π d²/4 and R = V/I from Ohm's law.

Why the others are wrong:

• A gives too small d, yielding unrealistically high R and V for the setup.
• B gives moderate d but mismatches calculated A from given parameters.
• C gives larger d but underestimates R compared to required value.

Final answer: D