4. Why do people sometimes use credit to pay for items instead of just using cash?
2 answers:
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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
Hence, Number of bulbs which can be lit using 1 kg of coal = 9