Posted by Kristie on .
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 13 % to 104 V.(Caution: The 1200- W label is valid only when 120 V is applied. When the voltage is lowered, it is the resistance of the toaster, not its power, that remains constant.)
1)By how much does the current decrease?
2)By how much does the power decrease?
R = 120V / 10A = 12 Ohms.
1. I = V/R = 104 / 12 = 8.67 Amps.
Change = 10 - 8.67 = 1.33 Amps.
2. P = VI = 104 * 8.67 = 902 Watts.
Change = 1200 - 902 = 298 Watts.