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?
To determine the answers to both questions, we need to use the relationship between voltage, current, and power in an electrical circuit.
1) To find out how much the current decreases, we need to compare the initial current at 120 V to the new current at 104 V.
Using Ohm's Law, we can determine the initial current:
Current (I) = Power (P) / Voltage (V)
I = 1200 W / 120 V
I = 10 A
Now, let's calculate the new current at 104 V:
I_new = 1200 W / 104 V
To find the current decrease, subtract the new current from the initial current:
Current decrease = I - I_new
2) To determine how much the power decreases, we need to compare the initial power at 120 V to the new power at 104 V.
Using the formula:
Power (P) = Voltage (V) * Current (I),
we can calculate the initial power:
P = 120 V * 10 A
P = 1200 W
Now, let's calculate the new power at 104 V:
P_new = 104 V * I_new
To find the power decrease, subtract the new power from the initial power:
Power decrease = P - P_new
Note: The resistance of the coffee maker remains constant when the voltage is decreased, but the power rating on the label is only valid when 120 V is applied. So, the power actually decreases when the voltage is lowered.