3 a. In a wood fire, 70% of the chemical energy in wood is changed to thermal energy. The remaining energy is changed to light and waste chemicals. Calculate the percentage of the chemical energy in the wood that is changed to light and waste chemicals. b. In an oil-burning power station, 55% of the chemical energy in the oil is changed to thermal energy and 10% is used in the power station. The remainder is changed to electrical energy. Calculate the percentage of the chemical energy in the oil that is changed to electrical energy. 4. Sofia has an LED flashlight that uses 18 J of electrical energy. 7 J of the electrical energy is wasted as thermal energy. Sofia says that 12 J of the electrical energy is changed to light. Explain whether Sofia is correct.
Answer (1)
Let's tackle each part of the question step by step.
3a. In a wood fire, we're told that 70% of the chemical energy is converted into thermal energy. We need to find the percentage of energy converted into light and waste chemicals.
Since the total energy conversion must add up to 100%, the remaining energy, which changes into light and waste chemicals, can be calculated by subtracting the thermal energy percentage from 100%.
100% − 70% = 30%
So, 30% of the chemical energy in the wood is changed to light and waste chemicals.
3b. In an oil-burning power station, 55% of the chemical energy is converted to thermal energy, and 10% is used in the power station. We need to calculate the percentage of the chemical energy converted to electrical energy.
First, add the percentages of energy not converted to electrical energy (thermal and station use):
55% + 10% = 65%
Subtract this from the total 100% to find the percentage converted to electrical energy:
100% − 65% = 35%
Therefore, 35% of the chemical energy in the oil is changed to electrical energy.
Sofia's LED flashlight uses 18 J of electrical energy, with 7 J being wasted as thermal energy. Sofia claims that 12 J is changed to light energy.
First, calculate how much energy is not wasted as thermal energy:
18 J − 7 J = 11 J
This means only 11 J could be converted into light energy. Therefore, Sofia's claim that 12 J is converted into light energy is incorrect. In fact, only 11 J could be used for light.
I hope this explanation helps you understand the concepts of energy conversion using these examples!
