Question

Burning coal yields about 30 x 106 joules of energy per kilogram of coal burned, but only 30% of that energy goed into electricity. How many 100 Watt light bulbs can be lit for one hour using 1 kilogram of coal?

Answer 1

Number of bulbs which can be lit using 1 kg of coal = 9

Explanation:

Energy yielded by burning 1 kg of coal = 30 × 106 joules

= 3180 joules

Amount of energy that can be used for electricity = 30 % of 3180 joules

= 0.30 × 3180

= 954 joules

Energy needed for lighting one bulb = Wattage of bulb × No. of hours of lighting

⇒ Energy needed for lighting one bulb = 100 × 1

= 100 joules

`\text{Now, Number of bulbs which can be lit for one hour = }(954)/(100)\\\\\implies\bf\textbf{Number of bulbs = }9.54\approx 9`

Hence, Number of bulbs which can be lit using 1 kg of coal = 9