Energy Resources and Transfers

Topic 1: Energy

Energy Stores and Systems

  • Energy Definition: Energy is never used up; rather, it is transferred between different energy stores and objects.

Energy Stores

  • Key Energy Stores:1.Thermal Energy Stores (also known as internal energy stores)
    2. Kinetic Energy Stores
    3.Gravitational Potential Energy Stores
    4.Elastic Potential Energy Stores
    5.Chemical Energy Stores
    6.Magnetic Energy Stores
    7.Electrostatic Energy Stores
    8.Nuclear Energy Stores

Energy Transfer Mechanisms

  • Energy is transferred in various ways:-
    Mechanically (via a force doing work)

  • Electrically (work done by moving charges)

  • By heating (due to temperature difference)

  • By radiation (e.g., light, sound, infrared)

Energy Transfer in Systems

  • Definition of a System: A system can be a single object (e.g., air in a piston) or a group of objects (e.g., colliding vehicles) being studied.

  • Energy Transfer During Changes:-
    Energy can be transferred into or out of the system or between different objects or energy stores.

  • Closed Systems: These systems do not exchange matter or energy with the environment. The total energy change in a closed system is always zero.

Energy Transfer by Heating

  • For example, when boiling water in a kettle, the kettle's heating element transfers energy to the water, raising its temperature. The water acts as the system in this context.

Energy Transfer by Doing Work

  • Work done is synonymous with energy transferred. Work can be done when a current flows through a circuit or when a force moves an object.

  • Examples of Work Done:-
    Throwing a ball upwards transfers chemical energy from the person's arm to the kinetic energy of the ball.

  • A ball falling transfers gravitational potential energy to kinetic energy.

  • Car brakes slowing down transfer kinetic energy to thermal energy in the surroundings.

  • In collisions, energy can be transferred to elastic potential energy stores, thermal energy stores, and sound energy.

Kinetic Energy and Potential Energy Stores

Kinetic Energy

  • Definition: Moving objects have energy stored in their kinetic energy store.

  • Energy Dependence: The kinetic energy of an object is dependent upon its mass (m) and speed (v).

  • Formula:-
    Kinetic Energy (Ek): Ek = \frac{1}{2}mv^2

  • Example Calculation:-
    For a car with mass 2500 kg traveling at 20 m/s: -
    E_k = \frac{1}{2} \times 2500 \times (20)^2 = 500,000 \text{ J}

Gravitational Potential Energy (G.P.E.)

  • Definition: Available energy in an object held within a gravitational field.

  • Energy Dependence: G.P.E. depends on mass, height, and the strength of gravitational field.

  • Formula: -
    Change in Gravitational Potential Energy (E): E = mgh

    Where:

  • m = mass (kg)

  • g = gravitational field strength (N/kg)

  • h = height (m)

  • Energy Transfer: When an object falls, energy from its G.P.E. converts into kinetic energy.

Elastic Potential Energy

  • Definition: Energy stored in springs or elastic materials when stretched or compressed.

  • Formula: -
    Elastic Potential Energy (Ee): Ee = \frac{1}{2} k e^2

    Where:

  • k = spring constant (N/m)

  • e = extension (m)

Specific Heat Capacity

  • Definition: The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C.

  • Energy Transfer Formula:-
    \text{Change in thermal energy (ΔE)} = mc \text{Δ} \theta

    Where:

  • m = mass (kg)

  • c = specific heat capacity (J/kg°C)

  • Δθ = change in temperature (°C)

  • Comparison of Materials:-
    Water: 4200 J to warm 1 kg by 1°C

  • Mercury: 139 J to warm 1 kg by 1°C

Practical Investigation of Specific Heat Capacity

  1. Prepare a block of material with a heating element and thermometer.

  2. Insulate the block to limit energy loss.

  3. Measure starting temperature, heat with a known potential difference.

  4. Record temperature increases over time to analyse energy transfer.

Conservation of Energy and Power

Conservation Principle

  • Definition: Energy cannot be created or destroyed; it can only change forms.

  • Dissipated Energy: Energy that is wasted, often transferred into thermal stores that are not useful.-
    Example: A mobile phone transforming chemical energy from its battery into thermal energy when being used.

Power

  • Definition: The rate of energy transfer or work done per second.

  • Unit: Power is measured in watts (W). 1 W = 1 J/s. _

  • Power Calculation: -
    P = \frac{E}{t} \text{ or } P = \frac{W}{t}

    Where:

  • E = energy transferred (J)

  • W = work done (J)

  • t = time (s)

Example of Power Calculation

  • Motor A requires 8,000 J to lift a stunt performer in 50 s.

  • Power of Motor A: P = \frac{8000}{50} = 160 \text{ W}

Methods of Energy Transfer: Conduction, Convection and Radiation

Conduction

  • Process: Vibration of particles transfers energy within solids.

  • Characteristics: Has a high thermal conductivity; energy conduction continues until equilibrium is reached.

  • Examples in Houses: Heat conducted through solid walls from a warm interior to a cooler exterior, or through window panes, and along metal pipes.

Convection

  • Process: Particles move from hotter to cooler regions, typically in liquids and gases.

  • Characteristics: Warmer particles rise due to a decrease in density, leading to convection currents.

  • Practical Examples: In a room, a radiator heats air by conduction, causing warm air to rise and initiate convection currents throughout the room, distributing heat. Central heating systems rely on convection to circulate heated air or water.

Infrared Radiation

  • Process: Energy transfer by electromagnetic waves.

  • Characteristics: Does not require a medium for transfer; can travel through a vacuum.

  • Examples: Humans and objects warmer than their surroundings emit infrared radiation. This is how heat from the sun reaches Earth, and how a fireplace or a radiant heater warms a room directly without heating the air in between.

Reducing Unwanted Energy Transfers

Lubrication Techniques

  • Lubricants reduce frictional forces, minimising energy loss in systems.

Insulation Techniques

  • Methods: -
    Cavity walls with insulating air gaps - reduce conduction

  • Thick walls - low thermal conductivity.

  • Loft insulation - reduce convection

  • double-glazed windows to minimise heat loss.- reduce conduction

Practical Investigation of Insulating Effectiveness

  1. Test energy retention in insulated containers with boiled water to compare various materials.

Efficiency of Energy Transfers

  • Definition: The ratio of useful output energy to total input energy.

  • Efficiency Formula: -
    \text{Efficiency} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}}

  • Example Calculation: A blender with 70% efficiency and 600 W input results in a useful output of 420 W.

Energy Resources and Their Uses

Non-Renewable Resources

  • Sources: Coal, oil, natural gas.

  • Characteristics: Finite, reliable, and environmentally damaging.

Renewable Resources

  • Sources: Solar, wind, hydroelectric, tidal, geothermal, bio-fuels.

  • Characteristics: Sustainable but can be less reliable; less environmental impact.

Example of Energy Production Types

  • Hydro-electric power uses falling water to generate energy.

  • Solar cells convert sunlight directly into electricity, typically used in remote areas.

Environmental Impact of Energy Production

  • Non-renewables increase CO2 and sulfur emissions, causing global warming and acid rain.

  • Renewable methods have less pollution but can disrupt habitats and landscapes.

Trends in Energy Resource Use

Historical Trends

  • The UK has seen a dependency on fossil fuels, but shifts towards renewables are influenced by factors such as reliability, cost, and public pressure.

Public Awareness

  • Awareness of environmental impact leads to an increased demand for renewable resources.