Question

2. Two bulbs rated as 100W, 220 V and 40W, 220V are connected in series to a 220V supply.
which bulb will produce more heat and which bulb will glow brighter?
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Answer 1

Always, When two bulbs of the same voltage and different wattages are connected in series, the lower wattage bulb will glow brighter. The reason is simple, they both see the same current, amperage, because they are in series. One of the Power dissipation formulas for resistive loads is that Power equals amperage squared times resistance. Amperage is constant, because the loads are in series, therefore the amperage squared is the same for both bulbs. . Therefore, in this case, the power is directly proportional to resistance. There is no question that the 40w bulb has a higher resistance than the 60w bulb; so the 40w bulb will dissipate more wattage and therefore be brighter.