In periods of peak demand, power companies lower their...

In periods of peak demand, power companies lower their voltage. This saves them power (and saves you money!). To see the effect, consider a 1200-W coffeemaker that draws 10 A when connected to 120 V. Suppose the voltage is lowered by 10% to 108 V. By how much does the current decrease? By how much does the power decrease? (Caution: The 1200-W label is valid only when 120 V is applied. When the voltage is lowered, the current is lowered, so the power output of the toaster’s heating coils drops, which cools the coil and lowers its resistance. However, for this problem assume the change in resistance is slight.)

In periods of peak demand, power companies lower their voltage. This saves them power (and saves you money!). To see the effect, consider a 1200-W coffeemaker that draws 10 A when connected to 120 V. Suppose the voltage is lowered by 10% to 108 V. By how much does the current decrease? By how much does the power decrease? (Caution: The 1200-W label is valid only when 120 V is applied. When the voltage is lowered, the current is lowered, so the power output of the toaster’s heating coils drops, which
cools the coil and lowers its resistance. However, for this problem assume the change in resistance is slight.)

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Key Concepts

Ohm’s Law

Ohm’s Law explains the relationship between voltage, current, and resistance in an electrical circuit, stating that current is directly proportional to voltage when resistance is constant. This principle allows one to calculate changes in current when the applied voltage is altered, as in the case where a reduction in voltage leads directly to a proportionate decrease in current.

Electric Power Calculation

Electric power is the product of voltage and current (P = IV). This concept is crucial when examining how changes in voltage affect power output, particularly under the assumption of constant resistance. A decrease in voltage will result in a decrease in both current and power, and the power output will drop more significantly due to its dependence on both variables.

Proportional Relationships in Circuits

The proportional relationship between voltage and current in a fixed-resistance circuit means that a specific percentage drop in voltage results in an equivalent percentage drop in current. Since power is the product of voltage and current, the effect on power is compounded, demonstrating that reductions in voltage can lead to larger relative decreases in power consumption.

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