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## Q. 1.2

There are approximately $12\times 10^{9}$ bulbs on earth. Assuming an average on
period of 6 hours and 50Waverage power, find the amount of coal required to produce
the same amount of energy for 1 day. Assume that the thermal energy of coal is 3 ×
$10^{4}$ J/kg and the efficiency of the conversion of the energy is 100%

## Verified Solution

The required energy for the bulbs per day is

$w_{b} =12\times 10^{9}\times 50\times 6 \times 60\times 60=1.296\times 10^{16} J$.

The corresponding amount of coal can be found as

$13\times 10^{4} \times m_{c} =1.296\times 10^{16} \longrightarrow m_{c} =432\times 10^{9} kg$.