Energy Stores and Transfers Quiz

Energy Stores and Transfers

• Energy exists in various stores: chemical, kinetic, gravitational potential, elastic potential, and thermal.
• Energy can be transferred via heating, waves, electric current, or force.
• Chemical energy is stored in fuels, food, and batteries.
• Kinetic energy is possessed by moving objects.
• Gravitational potential energy is stored in objects at height.
• Elastic potential energy is stored in stretched or compressed objects.
• Thermal energy is stored due to an object's temperature.

Energy Conservation

• Energy cannot be created or destroyed; only transferred or transformed.
• Examples: Torch (chemical → electrical → light/thermal), Falling object (gravitational potential → kinetic → thermal/sound).

Closed Systems

• In a closed system, energy can change forms but not enter or leave.

Energy Transfers in Specific Examples

• Roller coasters: Gravitational potential energy transforms to kinetic energy, with some loss to thermal and sound.
• Pendulums: Energy shifts between gravitational potential and kinetic, eventually dissipating due to air resistance.
• Bungee jumping: Gravitational potential, kinetic, and elastic potential energy are exchanged.

Useful vs. Wasted Energy

• Useful energy is directed to its intended goal. Wasted energy is not used efficiently.
• Friction causes energy loss (e.g., heating drill bits, brake pads).
• Exercise results in thermal energy, heating muscles.
• Energy spreads out; becoming less useful for work (dissipation).

Efficiency

• Efficiency (%) = (useful output energy / total input energy) * 100.
• Efficiency cannot exceed 100%.
• Higher efficiency means less wasted energy.
• Methods to improve efficiency include reducing friction.

Energy Sources and Appliances

• Common home energy sources: electricity, gas, oil.
• Electrical appliances include washing machines, microwaves, kettles.
• Clockwork radios are an alternative powered by winding up a spring.

Power

• Power (W) = Energy transferred (J) / Time (s).
• Power is measured in watts (W).

Energy Transfer by Conduction

• Energy transfer by conduction depends on temperature difference, material thickness, and thermal conductivity.
• Metals are good conductors; wood and glass are poor conductors.
• Insulation minimizes energy transfer, crucial for warmth.

Specific Heat Capacity

• Specific heat capacity (c) = ΔE / (m * Δθ), where ΔE is energy transferred, m is mass, and Δθ is temperature change.
• Factors affecting heat transfer include the mass and specific heat capacity of an object.

Changes of State

• States of matter: solids, liquids, gases.
• Particle arrangement: Solids (tightly packed), Liquids (close but mobile), Gases (far apart and highly mobile).
• Melting/boiling require energy from surroundings; freezing/condensing release energy.
• Latent heat is transferred without temperature change during phase transitions.
• Melting point is the temperature at which a solid turns to a liquid.
• Boiling point is the temperature at which a liquid turns to a gas.
• Evaporation occurs at any temperature, boiling only at the boiling point.
• Temperature-time graphs show changes of state.

Internal Energy

• Internal energy is the energy stored by the particles in a substance, comprising kinetic and potential energy.
• Increasing temperature increases internal energy as particles gain energy.