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Energy—How Things Work - Energy Conservation in Daily Life

Grade 5CBSE

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

🔑Concepts

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Energy is the capacity to do work. It exists in many forms such as mechanical, heat, light, sound, electrical, and chemical energy.

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The Law of Conservation of Energy states that energy can neither be created nor destroyed; it can only be converted from one form to another. The total energy remains constant, represented as Etotal=constantE_{total} = \text{constant}.

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Energy Transformation is the process of changing energy from one form to another. For example, a battery converts chemical energy into electrical energy.

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Renewable energy sources, like solar energy from the Sun, wind energy, and hydro energy, are sustainable and help in energy conservation because they do not run out.

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Non-renewable energy sources, such as coal, petroleum, and natural gas, are limited in nature. We must conserve energy to ensure these resources last longer.

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Simple ways to conserve energy in daily life include switching off lights when not in use, using LED bulbs which consume less power, and preferring public transport or bicycles over private cars.

📐Formulae

Etotal=PE+KEE_{total} = PE + KE

W=F×dW = F \times d

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

💡Examples

Problem 1:

An electric oven uses 2500 J2500\text{ J} of electrical energy to produce 2100 J2100\text{ J} of heat energy. How much energy is wasted as sound or light energy?

Solution:

Total energy input = 2500 J2500\text{ J}. Useful heat output = 2100 J2100\text{ J}. Wasted energy = Total input - Useful output.

2500−2100400\begin{array}{r} 2500 \\ - 2100 \\ \hline 400 \end{array}

The wasted energy is 400 J400\text{ J}.

Explanation:

According to the Law of Conservation of Energy, the total energy input must equal the total energy output (useful + wasted). By subtracting the useful heat from the total electrical energy, we find the energy lost to other forms.

Problem 2:

A ball sitting on a shelf has a Potential Energy (PEPE) of 45 J45\text{ J}. As it falls, it gains Kinetic Energy (KEKE). If its KEKE becomes 20 J20\text{ J} halfway down, what is its PEPE at that moment, assuming total energy is conserved?

Solution:

Total Energy E=PE+KEE = PE + KE. Initially, E=45 J+0 J=45 JE = 45\text{ J} + 0\text{ J} = 45\text{ J}. At the halfway point:

45−2025\begin{array}{r} 45 \\ - 20 \\ \hline 25 \end{array}

The PEPE at that moment is 25 J25\text{ J}.

Explanation:

Since energy is conserved, the sum of PEPE and KEKE must always equal the initial total energy (45 J45\text{ J}). To find the remaining PEPE, we subtract the current KEKE from the total energy.