A.3.1—Conservation of energy
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- HL
Conserve Energy in a System
Energy is conserved
Energy cannot be created or destroyed. In a defined system, energy is transferred between stores or across the system boundary, so the total energy accounting remains balanced.
Define the system first
Name the objects included and identify transfers by work, heating, radiation or electrical means. A falling object may transfer gravitational potential energy to kinetic energy, internal energy or sound.
Follow the chain
Write the initial store, the useful output store and any dissipated or transferred energy. A Sankey diagram or energy-flow statement should account for all significant branches.
Common trap
Energy “lost” from a useful store has been transferred elsewhere; it has not disappeared.
A.3.1 Exam Analysis
Assessment in practice
2–4 marksHow it is assessed
The evidence asks learners to outline energy changes in a pumped-storage hydroelectric system or describe gravitational potential energy becoming internal energy of air.
Command terms
Outline / Describe
What earns marks
Name the initial and final energy stores and identify the transfer pathway, including useful output and dissipated energy. For a pumped-storage system, track gravitational potential energy of water through kinetic/mechanical energy to electrical output.
Watch for
Listing energy forms without stating the direction of transfer or omitting the dissipated/internal-energy branch.
Representative question
Question 1
[Maximum number: 2]
Outline, with reference to energy changes, the operation of a pumped storage hydroelectric system.
PE of water is converted to KE of moving water/turbine to electrical energy «in generator/turbine/dynamo»
idea of pumped storage, ie: pump water back during night/when energy cheap to buy/when energy not in demand/when there is a surplus of energy
Retrieve the A.3 Work, Energy and Power Model
Account for energy
Define the system, identify energy stores and describe transfers. Work done by a force transfers energy; total energy is conserved even when mechanical energy is not.
Use the mechanical model
E_k= rac12mv^2,\quad \Delta E_{p,g}=mg\Delta h,\quad E_{p,elastic}= rac12k(\Delta x)^2
Conserve their sum only when resistive transfers are absent or included explicitly.
Use rates and ratios
P= rac{\Delta E}{\Delta t}=Fv,\qquad \eta= rac{E_{useful}}{E_{input}}= rac{P_{useful}}{P_{input}}
Fuel energy density connects available input energy to a chosen volume.
Final checks
Check the system boundary, signs of work and potential-energy changes, the reference height, extension from natural length, and whether the quantity is energy, power, efficiency or energy density.