Question

A 160 W lightbulb is plugged into a standard 120 V outlet.
(a) How much does it cost in dollars per 31-day month to leave the light turned on continuously? Assume electrical energy costs US$ 0.06/kW.h.
(b) What is the resistance of the bulb? (c) What is the current in the bulb?

Answer 1

(a) Cost of energy is $44.64

(b) Resistance of bulb is 90 ohm

(c) Current in the bulb is 1.333 A

Given:

P = 160 W

V = 120 volt

(a)

We have given time t = 31 days

We know that 1 day = 24 hour

So 31 days = 31*24 =744 hour

Power = 160W

Energy =Power * Time

Energy = 160W * 744 hour

Energy =119.04kWh

The cost of energy is $0.06 per kWh

So total cost of 744 watt = 744*0.06=44.64

(b)

We know that power is given by :

$P=\frac{V^2}{R} \\\\160=\frac{120^2}{R}\\\\ R=90ohms$

(c) Current in the bulb is given by:

$I=\frac{V}{R}\\\\ I=\frac{120}{90}\\\\ I=1.33A$

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