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Energy Forms and Transfers - Renewable and Non-renewable Energy Sources

Grade 6IB

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

🔑Concepts

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Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed from one form to another. The total energy in a closed system remains constant, expressed as Etotal=Euseful+EwasteE_{total} = E_{useful} + E_{waste}.

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Non-renewable Energy: Energy sources that exist in finite amounts and take millions of years to form. These include fossil fuels like coal, oil, and natural gas, as well as nuclear fuels such as Uranium (235U^{235}U).

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Renewable Energy: Sources that are naturally replenished on a human timescale. Examples include Solar (photovoltaic cells), Wind (kinetic energy), Hydroelectric (gravitational potential energy of water), and Geothermal (heat from the Earth's core).

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Energy Transfers and Transformations: For example, in a coal power plant, Chemical Potential Energy →\rightarrow Thermal Energy →\rightarrow Kinetic Energy →\rightarrow Electrical Energy.

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Environmental Impact: Burning fossil fuels releases Greenhouse Gases (GHGs) such as Carbon Dioxide (CO2CO_2) and Methane (CH4CH_4), which contribute to the Greenhouse Effect and global warming.

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Efficiency: This is the ratio of useful energy output to the total energy input. No machine is 100%100\% efficient because some energy is always 'lost' as heat energy (QQ) due to friction.

📐Formulae

Ek=12mv2E_k = \frac{1}{2} m v^2

Ep=m⋅g⋅hE_p = m \cdot g \cdot h

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

W=F⋅dW = F \cdot d

💡Examples

Problem 1:

A wind turbine captures 2500 J2500 \text{ J} of kinetic energy from the wind. If it produces 750 J750 \text{ J} of electrical energy, calculate its efficiency.

Solution:

Using the efficiency formula: Efficiency=7502500×100=30%\text{Efficiency} = \frac{750}{2500} \times 100 = 30\%.

Explanation:

The turbine converts 30%30\% of the wind's kinetic energy into useful electricity, while 70%70\% (1750 J1750 \text{ J}) is dissipated as sound and heat energy.

Problem 2:

Identify the energy transformation in a hydroelectric dam and calculate the potential energy of 10 kg10 \text{ kg} of water held at a height of 20 m20 \text{ m} (Assume g≈9.8 m/s2g \approx 9.8 \text{ m/s}^2).

Solution:

Transformation: Ep→Ek→Electrical EnergyE_p \rightarrow E_k \rightarrow \text{Electrical Energy}. Calculation: Ep=10 kg×9.8 m/s2×20 m=1960 JE_p = 10 \text{ kg} \times 9.8 \text{ m/s}^2 \times 20 \text{ m} = 1960 \text{ J}.

Explanation:

The gravitational potential energy (EpE_p) of the water depends on its mass (mm), the acceleration due to gravity (gg), and its height (hh).