# A 60 W kitchen light is left on for an entire year. If the cost of electricity is $0.08 per kWxh, what did it cost to leave on the light bulb ? ## Steps please ##### 1 Answer Apr 12, 2018 #### Answer: $42.08, or $42.05 #### Explanation: $1 W$is $1$watt. $1$watt of power means that $1$joule of energy is used in $1$second. therefore, the number of watts shows how many joules of energy are used in a second. $1 k W$is $1000$watts. this means that $1000$joules of energy are used in $1$second. $1 k W h$shows the amount of energy used at the same rate of $1 k W$in an hour. $1 k W$means that $1000$joules are used in a second. $1$hour is $3600$seconds. therefore, $1000$joules per second is the same rate as $3600 \cdot 1000$joules per hour. $3600 \cdot 1000 = 3 , 600 , 000$therefore, $1 k W h$is equal to $3 , 600 , 000$joules. - in a $60 W$light bulb, $60$joules are used every second. if you count $1$year as $365.25$days, then $1$year has $31 , 557 , 600$seconds. if $60$joules are used per second, then $1 , 893 , 456 , 000$joules are used in $31 , 557 , 600$seconds. $1 k W h$is $3 , 600 , 000$joules. $1 , 893 , 456 , 000$joules is $\frac{1 , 893 , 456 , 000}{3 , 600 , 000} k W h$. this is $525.96 k W h$. $0.08 * 525.96 is $42.08 to $2$decimal places. if the $60 W$light bulb is left on for $365.25$days, then it will cost $42.08.

if you count $1$ year as $365$ days, then $1$ year has $31 , 536 , 000$ seconds.

if $60$ joules are used per second, then $1 , 892 , 160 , 000$ joules are used in $31 , 536 , 000$ seconds.

$1 k W h$ is $3 , 600 , 000$ joules.

$1 , 892 , 160 , 000$ joules is $\frac{1 , 892 , 160 , 000}{3 , 600 , 000} k W h$. this is $525.6 k W h$.

$0.08 * 525.6 is $42.05 to $2$ decimal places.
if the $60 W$ light bulb is left on for $365.25$ days, then it will cost \$42.05.