Rainbow is formed due to

Electric field at centre O of semicircle of radius $$a$$ having linear charge density $$\lambda $$ given as

A capacitor is charged with a battery and energy stored is U. After disconnecting battery another capacitor of same capacity is connected in parallel to the first capacitor. Then energy stored in each capacitor is

Two bulbs of (40 W, 200 V), and (100 W, 200 V). Then correct relation for their resistances