NEB Class 11 • Physics • Heat and Thermodynamics

Heat & Temperature: NEB Class 11 Physics Guide

Distinguish temperature, internal energy and heat transfer; then solve thermal expansion, calorimetry, phase-change and conduction problems with a clear energy boundary.

Thermal equilibrium and temperature scales
Expansion, heat capacity and calorimetry
Phase change, heat transfer and Nepal examples

Heat is energy transferred because of temperature difference.

Thermal language first

Where Heat and Temperature fit in NEB Physics

The topic connects measurement, molecular reasoning and energy conservation. The CDC Physics Grade 11 page is the Nepal scope checkpoint. The OpenStax temperature section defines thermal equilibrium and the zeroth law, while its heat chapter treats energy transfer and calorimetry.

Review Work, Energy & Power if energy accounting is weak and Elasticity before thermal-stress applications.

A measurable thermal state

Temperature, equilibrium and the zeroth law

If A is in thermal equilibrium with B, and B with C, then A and C are in thermal equilibrium. This zeroth-law logic makes thermometers possible. At equilibrium there is no net heat transfer between systems, though microscopic molecular motion continues.

Celsius and kelvin increments have the same size: T(K) = θ(°C)+273.15. A temperature change of 10°C equals 10 K, but a temperature of 10°C is not 10 K. Absolute temperature ratios require kelvin.

Worked example: scale conversion

25.0°C = 298.15 K. A rise from 25°C to 40°C is ΔT = 15°C = 15 K. Keep absolute temperature and temperature difference separate.

Misconception: Metal and wood left in the same room can share temperature yet feel different because heat-transfer rates to or from skin differ.

Size changes with temperature

Thermal expansion

For a small temperature range, linear expansion is ΔL = αL₀ΔT. Isotropic solids approximately satisfy area coefficient 2α and volume coefficient 3α. The OpenStax thermal-expansion section explains expansion joints and that a hole in a uniformly heated plate expands as if the removed material were present.

Worked example: bridge component

A 20 m steel length with α = 12×10⁻⁶ K⁻¹ warms by 30 K. ΔL = 12×10⁻⁶×20×30 = 7.2×10⁻³ m = 7.2 mm. Real engineering allowances require codes and safety factors beyond this ideal calculation.

If expansion is completely constrained within a linear elastic model, thermal stress magnitude can be related to YαΔT. Uneven heating can create differential stress, which is why sudden temperature changes can crack some materials.

Energy in transit

Heat capacity and specific heat

For no phase change and negligible work, Q = mcΔT. Specific heat c is energy needed per unit mass per kelvin; heat capacity C = mc belongs to a particular object. The OpenStax heat-capacity treatment emphasises dependence on material, mass and temperature change.

Quantity	Definition	SI unit
Heat transfer Q	Energy crossing boundary due to ΔT	J
Specific heat c	Q/(mΔT)	J kg⁻¹ K⁻¹
Heat capacity C	Q/ΔT = mc	J K⁻¹
Latent heat L	Q/m during phase change	J kg⁻¹

Worked example: warming water

For 0.50 kg water, c = 4200 J kg⁻¹ K⁻¹, warmed by 20 K: Q = 0.50×4200×20 = 42,000 J. Positive Q denotes energy transferred into the chosen water system.

Energy balance

Calorimetry and final temperature

Define the system and assume an insulated exchange only when stated. Then total heat transfer inside the system sums to zero: ΣQ = 0, or heat lost by hotter parts equals heat gained by colder parts. Include the calorimeter’s heat capacity if the problem provides it.

Worked example: mixing water

0.20 kg water at 80°C mixes with 0.30 kg water at 20°C, with negligible loss and equal c. 0.20(80−T) = 0.30(T−20). Solving gives T = 44°C, sensibly between initial temperatures and closer to the larger cold mass.

Worked example: hot metal in water

A 0.10 kg metal at 100°C with c = 400 J kg⁻¹K⁻¹ enters 0.20 kg water at 20°C. Neglect container and loss. Solve 0.10×400(100−T) = 0.20×4200(T−20), giving T ≈ 23.6°C. Water’s much larger heat capacity keeps the final value near 20°C.

Energy without temperature change

Phase change and latent heat

During an ideal phase change at fixed pressure, transferred energy can change molecular arrangement while temperature remains constant. Use Q = mL for the phase-change stage. Multi-stage heating requires separate terms for warming, phase change and further warming.

Worked example: melt then warm

To take 0.10 kg ice at 0°C to water at 20°C, use Q = mL_f + mc_wΔT. With L_f = 3.34×10⁵ J kg⁻¹ and c_w = 4200, Q = 33,400+8,400 = 41,800 J.

A flat part of a heating curve does not mean no energy transfer; it means the ideal model assigns that energy to phase change rather than rising temperature.

Three mechanisms

Conduction, convection and radiation

The OpenStax heat-transfer overview distinguishes conduction through stationary matter by interactions, convection through bulk fluid motion and radiation by electromagnetic waves. More than one mechanism can occur in the same situation.

Conduction

A metal spoon warms from contact and internal energy transfer along the solid.

Convection

Heated fluid expands, density changes and bulk circulation transfers energy.

Radiation

Thermal electromagnetic radiation transfers energy without requiring matter.

For steady one-dimensional conduction, rate P = kAΔT/L in a simple slab model. Greater conductivity and area increase the rate; greater thickness reduces it.

Worked example: wall conduction

A slab has k = 0.50 W m⁻¹K⁻¹, area 4.0 m², thickness 0.20 m and temperature difference 10 K. P = 0.50×4×10/0.20 = 100 W in the ideal steady model.

Daily-life transfer reasoning

Nepal-relevant applications

Sun-warmed roofs exchange energy by radiation, conduction through roofing and walls, and convection with air. A vacuum flask reduces conduction and convection across evacuated space and uses reflective surfaces to reduce radiation. Wool traps air and lowers heat-transfer rate; it does not “produce heat.”

Mountain cooking and boiling behaviour involve pressure as well as temperature; use the data and assumptions supplied in a Physics problem instead of importing an unverified fixed boiling point for every altitude. Safe building and appliance design requires current standards beyond classroom formulas.

Exam method

A reliable thermal solution

Define the system and energy boundary.
List initial state, final state and any phase changes.
Choose Q = mcΔT, Q = mL, expansion or rate relation.
Use a sign convention consistently.
Write an energy balance before numbers.
Convert mass, temperature differences and time to SI.
Check that final equilibrium temperature lies physically between suitable initial values.

Use the Heat & Temperature study guide for a spaced plan. For online or physical NEB tuition, call 9846662070 with one attempted calorimetry question.

Closed-book checkpoint

Practice tasks

Explain heat versus internal energy.
Convert −10°C to kelvin.
Find expansion of a 5 m rod for given α and ΔT.
Mix two masses of the same liquid and find final T.
Draw a multi-stage heating energy ledger.
Name conduction, convection and radiation in a cooking situation.
Predict the effect of doubling slab thickness on conduction rate.

Check: Final equilibrium temperatures and energy signs must agree with the direction of spontaneous heat transfer.

Frequently asked questions

Questions students ask about Heat and Temperature

Is heat stored in an object?

Heat is energy transferred because of temperature difference; internal energy is a property of the system state.

Can equal-temperature objects feel different?

Yes. Different thermal conductivities change the rate of energy transfer to or from skin.

Why is ΔT the same in Celsius and kelvin?

The scales have equal interval size, though their zero points differ.

When does Q = mcΔT fail?

It needs modification during phase change, when work or other energy transfers matter, or when c varies significantly.

Why must final mixing temperature lie between starting values?

For an insulated ordinary exchange without phase change or internal sources, energy flows hot to cold until an intermediate equilibrium.

Where can I get help with NEB Heat and Temperature?

For current online or physical tuition options, call 9846662070 and confirm timetable, class mode, teacher availability and fees.

References and next steps

Sources and related study guides

Continue with the Heat & Temperature Study Guide to organise revision and error correction. Scope and sources were checked on 2 August 2026; follow current CDC, NEB and college instructions if requirements change.

Measurement method

Thermometry, calibration and uncertainty

A thermometer uses a property that changes reproducibly with temperature. Good measurement requires thermal contact, time to approach equilibrium, a calibrated scale and a stated resolution. A cold sensor placed in hot liquid can alter the sample; a small sensor and sufficient sample reduce this disturbance.

Read liquid columns at eye level and avoid touching the sensing region. For a digital probe, wait for a stable reading and record its resolution. Repeat measurements where possible and report uncertainty consistent with the instrument, not more decimal places than evidence supports.

Calibration compares readings with known reference conditions over the range of use. Agreement at one point does not guarantee accuracy everywhere; zero-offset and scale-factor errors have different effects. In calorimetry, temperature uncertainty can dominate a small ΔT, so choose masses and starting temperatures that produce a measurable but safe change.

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