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?

Power P = 360 W

Energy E = 0.72 kWh

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

360 W, 0.72 kW-hour

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