The power rating on a light bulb indicates how much power it would dissipate whe

Question

The power rating on a light bulb indicates how much power it would dissipate when it is hooked to the standard household voltage of 120V (this rating does not mean that the light bulb always dissipates the same amount of power, assume that the resistance is constant in this case). a) How much power is dissipated in a light bulb that is normally rated at 75W, if instead we hook it up to a potential difference of 60? b) How much power is dissipated in a light bulb that is normally rated at 75W, if instead we hook it up to a potential difference of 120V?

Explanation / Answer

The power dissipated by the bulb can be given as (Irms^2)*R or Vrms^2/r Vrms=Vpeak/?2 Vrms=120/?2 a))P=75=Vrms^2/r => r=96 ohms for V=60V P= 60*60/2*96=18.75 Watt b)) Similarly for this case we get r=24ohms P=120*120/2*24=300 Watt

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