Question

a brand of lightbulb has a power of 15 w and an efficiency of 8.9%. how much power is wasted as heat by this lightbulb?

a. 13.67 w
b. 8.90 w
c. 1.34 w
d. 6.55 w

Explanation:

Step1: Calculate the power used effectively

The efficiency formula is $\text{efficiency}=\frac{\text{useful power output}}{\text{total power input}}$. Given efficiency $\eta = 8.9\%=0.089$ and total power input $P_{total}=15\ W$. The useful power output $P_{useful}=\eta\times P_{total}=0.089\times15 = 1.335\ W$

Step2: Calculate the power wasted as heat

The power wasted as heat $P_{wasted}=P_{total}-P_{useful}$. Substitute $P_{total} = 15\ W$ and $P_{useful}=1.335\ W$ into the formula. $P_{wasted}=15 - 1.335=13.665\approx13.67\ W$

Answer:

A. 13.67 W