Question

Ella wants to replace old bulbs of her home with new LED bulbs. She buys LED bulb that has inbuilt AC to DC converter of output 5 v and 2.5 A. If the LED is 75% efficient, what would be power dissipated? Also find work done by LED when it is connected to power supply and left for 1 hr 15 minutes?​

Answer 1

Power = I * V = 2.5 C/s * 5 J/C = 12.5 J/s = 12.5 watts

Regardless of the efficiency the power consumed is that used by the converter.

E = P * t = 12.5 J/s * 4500 s = 4500 J