Question

question 10 of 25
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. 1.22 j
b. 2.16 j
c. 5.98 j
d. 117.8 j

Explanation:

Step1: Calculate light - energy efficiency

The efficiency of the light - bulb for light energy is $\eta = 1.8\%=0.018$. So the efficiency for heat energy is $\eta_{heat}=1 - \eta$.
$\eta_{heat}=1 - 0.018 = 0.982$.

Step2: Calculate heat energy per second

Power is energy per unit time ($P=\frac{E}{t}$). Given $P = 120\ W$ and $t = 1\ s$, the total energy per second is $E_{total}=P\times t=120\ J$ (since $P = 120\ W$ means $120\ J$ of energy is consumed per second).
The heat energy per second $E_{heat}=\eta_{heat}\times E_{total}$.
$E_{heat}=0.982\times120\ J=117.84\ J\approx117.8\ J$.

Answer:

D. 117.8 J