In series combination, the same current flows through each bulb. As resistance
`R = V^(2)/P or R prop 1/P`. Therefore, the resistance of 40 W bulb is highest for the given three bulbs. Heat produced `H = I^(2) Rt or H prop R`, so maximum heat is produced in 40 W lamp. As a result of it 40 W lamp will glow more brightly than the other two bulbs.
