How much energy is used when the incandescent bulb is left on for 12 hours

You haven't told us the "wattage" rating of the bulb.  We'll just have to call it ' W ' .

The bulb uses energy at the rate of W watts, or 0.001W kilowatts.

In 12 hours, it uses 0.012W kilowatt-hours of energy.

= = = = =

W watts = W Joules/second

1 hour = 3600 seconds

12 hours = (12 x 3600) seconds

Energy = (W Joule/sec) x (12 x 3600 sec)

Energy =  43,200W Joules

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