IB MYP 4-5 Physics- Energy transformation and conservation- Study Notes - New Syllabus
IB MYP 4-5 Physics-Energy transformation and conservation- Study Notes
Key Concepts
- Energy transformation and conservation
Energy Transformation and Conservation
Energy Transformation and Conservation
Energy transformation (also called energy conversion) is the process of changing energy from one form to another.
Energy cannot be created or destroyed, but it can be transferred or transformed into different forms as per the Law of Conservation of Energy.
Law of Conservation of Energy
The total energy of an isolated system remains constant; energy can change forms but the total amount remains the same.
Mathematically: \( E_{\text{total initial}} = E_{\text{total final}} \)
Common Forms of Energy
- Kinetic Energy (KE): Energy due to motion — \( KE = \dfrac{1}{2}mv^2 \)
- Potential Energy (PE): Stored energy due to position — \( PE_{\text{gravitational}} = mgh \)
- Elastic Potential Energy: Stored energy in stretched or compressed springs — \( PE_{\text{elastic}} = \dfrac{1}{2}kx^2 \)
- Thermal Energy: Energy due to temperature; internal kinetic energy of particles.
- Chemical Energy: Energy stored in chemical bonds.
- Electrical Energy: Energy from the flow of electric charges.
- Nuclear Energy: Energy from changes in the nucleus of atoms.
Examples of Energy Transformations
- Electric fan: Electrical → Kinetic (rotating blades) + Sound + Thermal
- Hydroelectric dam: Gravitational potential → Kinetic (water flow) → Electrical
- Car engine: Chemical (fuel) → Thermal → Kinetic (wheels turning) + Sound
- Photosynthesis: Light → Chemical
Energy Efficiency
Efficiency measures how much input energy is converted to useful output energy.
\( \text{Efficiency} = \dfrac{\text{Useful Output Energy}}{\text{Total Input Energy}} \times 100\% \)
Key Points to Remember
- Energy can be transformed multiple times in a single process.
- In real-life processes, some energy is always lost as heat or sound due to friction or resistance.
- The sum of all forms of energy in a closed system remains constant.
Example:
A roller coaster car of mass \( 500 \, \text{kg} \) is at the top of a hill \( 40 \, \text{m} \) high. Assuming no friction, find the speed of the car at the bottom.
▶️ Answer/Explanation
At the top: \( PE_{\text{top}} = mgh = 500 \times 9.8 \times 40 = 196,000 \, \text{J} \)
At the bottom: All potential energy converts to kinetic energy — \( KE_{\text{bottom}} = \dfrac{1}{2}mv^2 \)
\( 196,000 = \dfrac{1}{2} \times 500 \times v^2 \)
\( v^2 = \dfrac{196,000 \times 2}{500} = 784 \)
\( v = 28 \, \text{m/s} \)
Final speed: \( \boxed{28 \, \text{m/s}} \)
Example:
A light bulb has a power rating of \( 100 \, \text{W} \) and produces \( 20 \, \text{W} \) of light energy. Find its efficiency.
▶️ Answer/Explanation
Efficiency = \( \dfrac{\text{Useful Output Energy}}{\text{Total Input Energy}} \times 100\% \)
= \( \dfrac{20}{100} \times 100\% \)
= \( \boxed{20\%} \)