Question

A hair dryer has a switch that allows it to be used in the US (where the AC voltage is 120 V) and in Europe (where the AC voltage is 230 V). It accomplishes this by having two different resistance settings. When the switch is in the "120 V" position, the hair dryer uses a resistance value that allows it to operate at its rated power of 1440 W when connected to 120 V, and when the switch is in the "230 V" setting, the hair dryer uses a resistance that allows it to still operate at its rated power of 1440 W when connected to 230 V. A tourist takes her 1440 W dual voltage hair dryer to Europe but forgets to set the switch to the "230 V" position. When she plugs it into the 230 V receptacle and turns it on, it begins to smoke. What power does the hair dryer consume as a result of this mistake?

Answer 1

5290 W

Step-by-step explanation:

Resistance of the drier in 1440W, 120V setting

= V² / W

= 120 x120 / 1440

= 10 ohm

Resistance of the drier in 1440W, 230V setting

= 230 x 230 / 1440

= 36.736 ohm

Now drier of 1440W, 120V setting

used in 230V

Power used by it

= V² / R

= 230 X 230 / 10

= 5290 W