First Law of Thermodynamics Study Guide: NEB 12 Physics

Study map

Organise every question around the energy ledger

The CDC page and curriculum control scope. Use three layers: state variables describe equilibrium; Q and W describe transfers during a path; the first law connects them. The concept guide provides detailed reference after retrieval.

Seven-session plan

Separate meaning, graph and calculation

1. System, state, equilibrium, temperature, heat, work and internal energy.
2. Sign convention and simple energy-ledger word problems.
3. P–V graphs, dW=P dV, path dependence and cycle area.
4. Isochoric and isobaric processes with worked comparisons.
5. Isothermal ideal-gas and adiabatic processes with conditions.
6. Heat capacities/ideal-gas internal energy at the taught depth.
7. Mixed timed numericals, explanations, derivations and practical graph questions.

Begin with closed-book definitions and finish with a contrast problem. Space review after 1, 3, 7 and 21 days. A correct sign obtained by luck is not mastery; explain the energy arrow.

Sign workshop

Draw arrows before equations

Draw Q arrow into the system for positive heat. Draw W arrow out for positive work by system. Expansion tends to W>0; compression W<0. Then use ΔU=Q−W. If a source uses work-on-system, translate once and do not mix conventions.

Practise four cases: heating while expanding; cooling while compressed; adiabatic expansion; compression with heat rejection. For each, predict ΔU sign before numbers. Check with the OpenStax first-law sign table.

P–V graph workshop

Use area and endpoints for different jobs

Endpoints determine state-function change when enough state information is known. The path determines work. A vertical line gives W=0. A horizontal line gives rectangular PΔV. A curved path needs integration or graph area. In a closed cycle, ΔU=0 and enclosed signed area equals net work.

Compare two paths between A and B: the path with larger pressure during expansion has larger work, therefore it needs larger heat input for the same ΔU. This is a reasoning answer before calculation. Use the thermodynamic-process chapter for examples.

Error repair

Record the first wrong thermodynamic decision

• Heat as state variable: rewrite heat as transfer.
• Mixed work convention: state W_by or W_on.
• Isothermal=adiabatic: distinguish ΔT=0 from Q=0.
• PΔV on curved path: use integral/area.
• Cycle ΔU nonzero: final state equals initial.

Redo closed-book and retest with fresh signs two days later. Keep this unit in the Class 12 roadmap.

Timed checkpoint

Use a forty-five-minute mixed review

1. Definitions and sign arrows.
2. Constant-pressure work and ledger.
3. Two-path P–V comparison.
4. Process table and one derivation.
5. Cycle interpretation and error audit.

For tuition call 9846662070. Use the MKS panel after Grade 12 for SAT/IELTS/PTE/DET and study-abroad pre-counselling.

Checked sources

References and related learning

• CDC Nepal: Physics Grade 12
• CDC Nepal: Secondary Curriculum
• OpenStax: Work, Heat and Internal Energy
• OpenStax: First Law
• OpenStax: Thermodynamic Processes
• PhET: Gas Properties

Apply the plan in the Practice Set. Sources were checked on 2 August 2026; follow current CDC, NEB and school notices if requirements change.