A variable resistor is connected to a constant voltage source. When the resistance is increased from 5.5 Ω to 9.3 Ω, what happens to the power dissipated?
A) no change
B) a 35% decrease
C) a 41% decrease
D) a 59% decrease
E) a 69% decrease

Question

Quizplus · Accepted Answer

The power dissipated in a resistor connected to a constant voltage source is given by $P = \frac{V^2}{R}$, where $P$ is the power, $V$ is the voltage, and $R$ is the resistance. When the resistance increases, the power dissipated decreases because the resistance is in the denominator. To find the percentage decrease, we calculate the power before and after the change and compare. The exact percentage isn't necessary to calculate because the relationship is inversely proportional, and among the given options, a 41% decrease is a reasonable approximation for the change from 5.5 Ω to 9.3 Ω.

A Variable Resistor Is Connected to a Constant Voltage Source