Question

a lightbulb has an efficiency of 1.8%. how much heat energy (not light energy) is generated by the bulb every second if the bulb has a power of 120 w?
a. 2.16 j
b. 1.22 j
c. 117.8 j
d. 5.98 j

Explanation:

Step1: Calculate the total energy per second

Power is energy per unit time. Given power \(P = 120\space W\), and \(P=\frac{E}{t}\), for \(t = 1s\), the total energy \(E_{total}=P\times t=120\times1 = 120J\)

Step2: Calculate the non - light (heat) energy

Efficiency \(\eta=1.8\%=\frac{E_{light}}{E_{total}}\). Then \(E_{heat}=E_{total}(1 - \eta)\)
Substitute \(\eta = 0.018\) and \(E_{total}=120J\) into the formula: \(E_{heat}=120\times(1 - 0.018)=120\times0.982 = 117.84J\approx117.8J\)

Answer:

C. 117.8 J