Question

A 100-watt light bulb illuminates a solar cell. The electricity from the solar cell operates a water pump that delivers 1 watt of power. What is the efficiency of the system?

Answer 1

Answer:

1 %

Explanation:

The efficiency of a system is defined as the ratio between the energy produced and the energy in input:

$\eta = \frac{E_{out}}{E_{in}}\cdot 100$

The same formula can also be rewritten in terms of the power produced and the power in input:

$\eta = \frac{P_{out}}{P_{in}}\cdot 100$

Since in this problem we have:

$P_{in}=100 W\\P_{out}=1 W$

The efficiency is

$\eta = \frac{1 W}{100 W}\cdot 100$=1 \%