Question

What is the power usage of a device that uses 3.0 A of current at a voltage of 120 V? How much energy (in kilowatt-hours) does this device use if it is left on for 2.0 hr?

Answer 1

360 W, 0.72 kW-hour

Step-by-step explanation:

Power = Voltage × Current

P = VI.............. Equation 1

Given: V = 120 V, I = 3 A.

Substitute into equation 1

P = 120(2)

P = 360 W.

Hence the power usage of the device = 360 W

Energy = Voltage×Current×time

E = VIt.............. Equation 2

Given: V = 120 V, I = 3 A, t = 2 hr.

Substitute into equation 2

E = 120(3)(2)/1000

E = 0.72 kW-hour

Hence the energy of the device in kWh = 0.72 kWh

Answer 2

Power P = 360 W

Energy E = 0.72 kWh

Step-by-step explanation:

Power can be expressed as a function of potential difference and current as;

Power = potential difference × Current

P = VI.............. 1

Given:

Potential difference V = 120 V

Current I = 3 A

Substituting the given values into equation 1

P = 120 × 2

P = 360 W

Therefore, the power usage of the device = 360 W

Energy is the product of potential difference, current and time.

Energy = Current×potential difference×time

E = iVt.............. 2

Given:

V = 120 V,

I = 3 A,

t = 2 hr.

Substitute into equation 2

E = 3×120×2 = 720 Wh ÷ 1000 kWh/Wh

E = 0.72 kWh

Therefore, the energy of the device in kWh = 0.72 kWh