Additional extension in remaining wires due to load redistribution

Steps:

• Initially, three identical wires each support tension W/3 and extend 0.4 cm by Hooke's law.
• After middle wire breaks, two wires each support W/2, so total extension per wire is (W/2)/(W/3) × 0.4 cm = 0.6 cm.
• Additional extension is 0.6 cm - 0.4 cm = 0.2 cm.
• Lamp height h decreases by this additional extension, so difference is 0.2 cm.

Why A is correct:

• Hooke's law states extension ∝ tension; additional tension W/6 per wire causes 0.2 cm extra stretch.

Why the others are wrong:

• B: Incorrect; 0.27 cm unrelated to proportional extension calculation.
• C: Wrong; 0.4 cm ignores that remaining wires start from initial 0.4 cm extension.
• D: Incorrect; equilibrium changes, so height must decrease.

Final answer: A