Science (Double Award) | Energy resources and energy transfer

👋 Welcome to Energy Resources and Transfer!

This chapter is fundamental to understanding how the world around us works! Energy powers everything—from your own body running a marathon to the huge generators powering cities. Don't worry if physics sometimes feels complicated; we'll break down these big ideas into simple, manageable pieces!

In this unit, we will learn about the different forms energy takes, the fundamental law that governs all energy changes, and how we harvest energy from the environment.
Let's get started!

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1. Energy Stores and Transfer Pathways

Energy isn't just one thing; it can be stored in different ways. Think of these stores as different bank accounts holding energy, and transfers as the ways money moves between accounts.

1.1. The Eight Main Energy Stores (Accounts)

When an object has energy, it is being held in one of these eight stores:

• Kinetic Energy (K.E.): Energy due to movement. (Example: A running athlete, a rolling car).
• Gravitational Potential Energy (G.P.E.): Energy stored in an object due to its position (height) in a gravitational field. (Example: Water held behind a dam).
• Chemical Energy: Energy stored in chemical bonds between atoms. (Example: Food, fuels like petrol, batteries).
• Thermal Energy (Heat): Energy related to the temperature of an object (the vibration of its particles). (Example: Hot tea, a radiator).
• Elastic Potential Energy: Energy stored in a stretched or squashed object. (Example: A bowstring pulled back, a stretched rubber band).
• Nuclear Energy: Energy stored in the nucleus of an atom. (Example: Nuclear power plants, the Sun).
• Electrostatic Energy: Energy due to the forces between electric charges. (Example: Two magnets attracting or repelling).
• Magnetic Energy: Energy due to the forces between magnetic poles. (Example: Two charged particles near each other).

✨ Memory Aid: Remember the key stores you’ll use most often: Kids Got Cool Toys Eating Nuts (K, G, C, T, E, N).

1.2. The Four Energy Transfer Pathways

Energy moves from one store to another (or from one object to another) via these pathways:

1. Mechanically: Transfer by a force moving an object. This is often called Work Done. (Example: A hammer hitting a nail).
2. Electrically: Transfer by moving charge (current) through a circuit. (Example: Plugging in and running a toaster).
3. By Heating: Transfer due to a temperature difference. (Example: Placing your hand on a hot object).
4. By Radiation: Transfer using waves (like light waves, infrared waves, or sound waves). (Example: A lamp giving off light).

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2. The Law of Conservation of Energy

This is the most crucial concept in all of energy physics!

The Fundamental Law

The Law of Conservation of Energy: Energy cannot be created or destroyed. It can only be transferred from one store to another or dissipated (spread out) into the surroundings.

This means that in any closed system, the total energy input must equal the total energy output.

Imagine throwing a ball straight up:

1. It starts with Kinetic Energy (K.E.).
2. As it rises, K.E. is transferred to Gravitational Potential Energy (G.P.E.).
3. At the highest point, K.E. is zero (momentarily stopped), and G.P.E. is maximum.
4. As it falls, G.P.E. is transferred back into K.E.

Energy is never lost! However, a tiny bit of energy is always transferred to the surroundings as wasted thermal energy (due to air resistance).

Wasted Energy (Dissipation)

When energy is transferred, some of it is always wasted or dissipated (spread out) into the environment, usually as thermal energy (heat) or sound.

Once energy has dissipated into the surroundings, it becomes much harder to use for the intended purpose, making it useless.

🚫 Common Mistake Alert! Never say "Energy is lost" or "Energy runs out." Say: "Energy is transferred to the surroundings as wasted thermal energy."

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3. Efficiency and Energy Calculations

Since we want devices to waste as little energy as possible, we measure their efficiency.

3.1. Defining Efficiency

Efficiency is a measure of how good a device is at converting the energy input into useful energy output, rather than wasting it.

A perfect device would be 100% efficient, but this is impossible in reality!

3.2. Efficiency Formulas

Efficiency is always calculated using the useful output divided by the total input. This ratio can be given as a decimal (between 0 and 1) or as a percentage (between 0% and 100%).

Formula 1: Using Energy (Joules, J)

$$Efficiency = \frac{Useful\ Energy\ Output}{Total\ Energy\ Input}$$

Formula 2: Percentage Efficiency (The most common form)

$$Percentage\ Efficiency = \frac{Useful\ Energy\ Output}{Total\ Energy\ Input} \times 100\%$$

Did you know? A modern lightbulb (LED) is around 80-90% efficient at producing light, while an old filament bulb was only about 5% efficient—wasting the rest as heat!

3.3. Power (The Rate of Energy Transfer)

Power is the rate at which energy is transferred or the rate at which work is done.

If you have two light bulbs, and one is 60 W and the other is 100 W, the 100 W bulb transfers more energy per second.

The unit for Power is the Watt (W). One Watt means that 1 Joule of energy is transferred every second (1 W = 1 J/s).

The Power Formula

$$Power\ (P) = \frac{Energy\ Transferred\ (E)}{Time\ Taken\ (t)}$$

Alternatively, since Work Done is just energy transferred:

$$Power\ (P) = \frac{Work\ Done\ (W)}{Time\ Taken\ (t)}$$

Example: A machine transfers 500 Joules of energy in 10 seconds. Its power is:

$$P = 500\ J / 10\ s = 50\ W$$

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4. Energy Resources: Supply and Demand

We rely on energy resources to generate electricity and power our transport. We classify these sources based on whether they will run out.

4.1. Non-Renewable Resources

These resources are being used up much faster than they can be naturally replaced. They are finite (limited supply).

A. Fossil Fuels (Coal, Oil, Natural Gas)

• Mechanism: Chemical energy stored in the fuel is converted to thermal energy (burning), which boils water to turn turbines.
• Advantages: Highly reliable (they work whenever needed); relatively cheap to extract and transport (historically).
• Disadvantages (Key Environmental Impacts):
  • Release large amounts of carbon dioxide (CO₂), which is a greenhouse gas contributing to global warming and climate change.
  • Release sulfur dioxide, which causes acid rain.
  • Finite supply—they will eventually run out.

B. Nuclear Fuel (Uranium, Plutonium)

• Mechanism: Nuclear energy is released by fission (splitting atomic nuclei), which generates massive thermal energy to boil water.
• Advantages: Very large energy output for a small mass of fuel; produces zero greenhouse gases (no CO₂ released).
• Disadvantages:
  • Produces extremely dangerous radioactive waste that must be safely stored for thousands of years.
  • High decommissioning cost (shutting down old plants).
  • Risk of catastrophic accidents (though rare).

4.2. Renewable Resources

These resources are naturally and continuously replenished. They are sustainable and will not run out.

A. Solar Energy

• Mechanism: Solar cells (photovoltaics) convert light energy directly into electrical energy.
• Disadvantages: Intermittent (only works when sunny); high cost of production; requires large areas for power generation.

B. Wind Energy

• Mechanism: Kinetic energy of wind turns the blades, rotating a turbine.
• Disadvantages: Intermittent (needs wind); can be noisy; visual pollution (some people find them ugly); risk to birds.

C. Hydroelectric Power (HEP)

• Mechanism: Water stored behind a dam (G.P.E.) falls, turning turbines.
• Advantages: Reliable (once the dam is full); flexible (can be turned on quickly when needed).
• Disadvantages: Expensive to build; requires flooding large valleys, destroying habitats and displacing people.

D. Tidal Energy

• Mechanism: Water moving in and out with the tides flows through large turbines.
• Advantages: Highly predictable (tides are predictable).
• Disadvantages: Only possible in certain coastal areas; impacts estuary ecosystems.

E. Geothermal Energy

• Mechanism: Thermal energy from hot rocks deep underground (often near volcanic activity) is used to heat water or drive turbines.
• Advantages: Reliable and constant supply.
• Disadvantages: Only available in limited geographical locations; high drilling/installation costs.

F. Biofuels

• Mechanism: Plants (or waste products) are grown, harvested, and burned to release chemical energy.
• Environmental Impact: Biofuels are sometimes considered carbon neutral because the CO₂ released when they burn was recently absorbed from the atmosphere by the plants during photosynthesis. However, transportation and processing still release CO₂.
• Disadvantages: Requires vast amounts of land that could be used for food crops (competition for resources); deforestation to clear land.