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

Answer:

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

Step-by-step 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

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

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