Question

Light bulbs are often rated by the wattage of the bulb, i.e. 60-watt or 90-watt rated bulbs are common. This can be misleading because if you attach the same bulb to different voltage sources they will produce a different power output. The rating is with the assumption that you are connect- ing it to a standard voltage, like the 120 volts that come from the wall outlet (for this problem lets ignore the effects of alternating current).

(a) If the wattage is not a constant of the bulb, what is, e.g. what would be a better constant property to use to define the features of the bulb? Explain.

(b) If you then attached a 60-watt and 90-watt rated bulb in series with a constant voltage source, which would you expect to shine brighter? Explain.

Answer 1

(a) Resistance of the bulb will always be constant regardless of which circuit it will be placed. From resistance we can get the power spend by the bulb by knowing the potential in which it is connected.

(b) In a series connection, the current through both the bulb remains same. So theglowing of the bulb that is the power dissipated will depend on resistance o the bulb only. More the resistance more will be the power and hence more is the glow.

Now for a bulb connected in a constant voltage source, the wattage is given by

So a bulb with high wattage has less resistance and hence will glow less brighter when connected in series. So the 60-watt bulb will shine brighter.