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Energy and Heat - Renewable and Non-renewable Energy Resources

Grade 7IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Energy is the ability to do work and is measured in Joules (JJ). The Law of Conservation of Energy states that energy cannot be created or destroyed, only transformed from one form to another.

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Non-renewable energy resources are finite and will eventually run out. These include fossil fuels (Coal, Oil, and Natural Gas) and Nuclear energy (UraniumUranium).

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Fossil fuels release greenhouse gases such as Carbon Dioxide (CO2CO_2) and Methane (CH4CH_4) when burned, contributing to the enhanced greenhouse effect and global warming.

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Renewable energy resources are replenished naturally over short periods. Examples include Solar (photovoltaic and thermal), Wind, Hydroelectric, Tidal, Geothermal, and Biomass.

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Thermal energy (Heat) moves from regions of higher temperature to regions of lower temperature through three main processes: Conduction (solids), Convection (fluids), and Radiation (infrared waves through vacuum).

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Energy efficiency measures how much of the input energy is converted into useful output energy, as opposed to 'wasted' energy (usually dissipated as thermal energy to the surroundings).

📐Formulae

Efficiency (%)=Useful Energy OutputTotal Energy Input×100\text{Efficiency (\%)} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \times 100

E=P×tE = P \times t

Q=mcΔTQ = mc\Delta T

Total Energy=Useful Energy+Wasted Energy\text{Total Energy} = \text{Useful Energy} + \text{Wasted Energy}

💡Examples

Problem 1:

A coal-fired power station takes in 1000 MJ1000 \text{ MJ} of chemical energy and produces 350 MJ350 \text{ MJ} of electrical energy. Calculate the efficiency of the power station.

Solution:

Efficiency=350 MJ1000 MJ×100=35%\text{Efficiency} = \frac{350 \text{ MJ}}{1000 \text{ MJ}} \times 100 = 35\%

Explanation:

To find the efficiency, we divide the useful energy output (350 MJ350 \text{ MJ}) by the total energy input (1000 MJ1000 \text{ MJ}) and multiply by 100 to get the percentage. The remaining 650 MJ650 \text{ MJ} is lost as waste heat.

Problem 2:

A wind turbine produces 5000 J5000 \text{ J} of electrical energy every second. How much total energy does it produce in 1 minute1 \text{ minute}?

Solution:

E=P×t=5000 J/s×60 s=300,000 J (or 300 kJ)E = P \times t = 5000 \text{ J/s} \times 60 \text{ s} = 300,000 \text{ J} \text{ (or } 300 \text{ kJ)}

Explanation:

Since power (PP) is the rate of energy transfer, we multiply the power (5000 W5000 \text{ W}) by the time in seconds (1 minute=60 seconds1 \text{ minute} = 60 \text{ seconds}) to find the total energy (EE).

Problem 3:

Explain why a solar panel is considered renewable while a piece of coal is not, referring to the time scales involved.

Solution:

Solar energy is derived from the Sun, which is expected to last for billions of years; its energy is replenished daily. Coal takes millions of years to form from decaying organic matter under high pressure and temperature (C+O2→CO2C + O_2 \rightarrow CO_2).

Explanation:

The classification depends on the rate of replenishment versus the rate of consumption. Since we consume coal much faster than it forms, it is non-renewable.