In a 3-phase, 4-wire, 400/230 V system, a lamp (L1) of 100 W is connected to one phase and neutral and a lamp (L2) of 150 W is connected to the second pahse and neutral. If the neutral wire is disconnected accidently, then

• A. both 100 W lamp (L1) and 150 W lamp (L2) becomes brighter
• B. 100 W lamp (L1) becomes dim and 150 W lamp (L2) becomes brighter
• C. both 100 W lamp (L1) and 150 W lamp (L2) becomes dim
• D. 100 W lamp (L1) becomes brighter and 150 W lamp (L2) becomes dim

Answer: (D)

When neutral disconnected, lamps are in series connection,
So, for series connection current is same for both Lamp,
So, Resistance of 100 W Lamp is more compared to 150 W Lamp.
Hence after neutral connection disconnect 100 W Lamp is more brighter than the 150 W Lamp.