Switch bypasses L2, altering current distribution

Steps:

• Initially, with S open, L1 and L2 are in series, sharing the total current equally.
• Closing S creates a short circuit across L2, bypassing it entirely.
• Current now flows only through L1, increasing its current and power dissipation.
• L2 receives no current, turning it off.

Why B is correct:

• By Ohm's law, L1's increased current (I = V/R_L1, full voltage across L1) raises its power (P = I²R), making it brighter; L2's zero current makes it dimmer.

Why the others are wrong:

• A: L2 cannot brighten as it's bypassed (zero current).
• C: L1 cannot dim with more current through it.
• D: L1 brightens due to full current, not dims.

Final answer: B