NEB Class 11 • Physics • Thermal Energy

Quantity of Heat: NEB Class 11 Physics Guide

Treat heat as energy in transit, not a substance stored in an object. Build temperature-change, mixture and phase-change calculations from a defined system boundary.

Q = mcΔT and heat-capacity models
Calorimetry energy ledgers and phase change
Worked Nepal examples, units and exam checks

Quantity of heat is energy transferred across a system boundary.

Curriculum boundary

What Quantity of Heat covers

The CDC secondary curriculum includes heat capacity, specific heat capacity, Newton’s law of cooling and related thermal ideas in Grade 11 Physics. Check the CDC Physics Grade 11 page for the current subject resource.

The definitions and equations here follow OpenStax Heat, temperature change and heat capacity, and its institutional calorimetry treatment. Numerical property values depend on conditions, so use values given by the exam or laboratory.

Precise language

Heat, temperature and internal energy are different

Temperature describes thermal state and is related to average microscopic energy. Internal energy is energy stored in the many microscopic degrees of freedom of a system. Heat is energy crossing the system boundary solely because of a temperature difference. Once transferred, call it a change in internal energy rather than “heat contained.”

Net heat transfer proceeds from higher to lower temperature until thermal equilibrium, unless an external device does work. Equal temperature does not imply equal internal energy: a large bucket of warm water may have more internal energy than a small cup at the same temperature.

Quantity	Meaning	SI unit
Q	Energy transferred by temperature difference	joule, J
T	Thermal state	kelvin, K
U	Microscopic energy stored in system	joule, J

Temperature-change model

Specific heat and heat capacity

For mass m whose temperature changes by ΔT without phase change, Q = mcΔT. Specific heat capacity c is energy per kilogram per kelvin, with unit J kg⁻¹K⁻¹. Heat capacity C = mc belongs to a particular object and has unit J K⁻¹. Thus Q = CΔT.

Worked example: heating water

Find energy to warm 2.0 kg of water from 20°C to 70°C using c = 4200 J kg⁻¹K⁻¹. ΔT = 50 K, so Q = 2.0×4200×50 = 4.2×10⁵ J. The same temperature interval is 50°C or 50 K.

Compare equal energy input

Equal 10 kJ transfers to 1 kg samples with c values 500 and 1000 J kg⁻¹K⁻¹. Their temperature rises are 20 K and 10 K. Larger specific heat means smaller change for the same mass and energy.

The formula is not automatic. If a phase change occurs, c varies greatly, energy escapes, or work matters, divide the process into appropriate stages.

Energy conservation

Calorimetry and the heat ledger

A calorimeter aims to limit energy exchange with surroundings. Define the system, predict which body cools and which warms, then write one Q term for every body. With the sign convention Q positive into a body, an ideal insulated mixture satisfies ΣQ = 0.

Worked example: mixing water

Mix 0.20 kg water at 80°C with 0.30 kg at 20°C in an ideal insulated container. Because c is common, 0.20(80−T_f) = 0.30(T_f−20). Solving gives T_f = 44°C, between the initial temperatures.

Metal dropped into water

A 0.10 kg metal with c = 400 J kg⁻¹K⁻¹ at 100°C enters 0.20 kg water at 20°C; take c_w=4200. Set 0.10×400(100−T)=0.20×4200(T−20). Solving gives T≈23.6°C. The result lies near water’s initial temperature because the water heat capacity is much larger.

If the calorimeter has heat capacity C_cal, include C_cal(T_f−T_cal,i). Ignoring it changes the inferred property and should be identified as a model limitation.

Energy without temperature change

Latent heat and multi-stage processes

During an ideal phase change at fixed pressure, energy changes molecular arrangement while temperature remains at the transition value. Use Q = mL, where L is specific latent heat in J kg⁻¹. The OpenStax latent heat section develops this distinction.

Melting ice

To melt 0.050 kg ice at 0°C using L_f = 3.34×10⁵ J kg⁻¹, Q = 1.67×10⁴ J. Temperature remains 0°C during the ideal melting stage.

Two-stage calculation

To melt the same ice and then warm the water to 20°C: Q = mL_f + mc_wΔT = 16,700 + 0.050×4200×20 = 20,900 J. Never merge a plateau and sloping stage into one mcΔT term.

Worked reasoning

Quantity of Heat examples in context

Electric kettle efficiency

A kettle draws 1.5 kW for 4.0 min and transfers 2.7×10⁵ J to water. Electrical input is Pt = 1500×240 = 3.6×10⁵ J, so energy-transfer efficiency is 75%. The remaining energy goes to kettle and surroundings.

Solar-heated water

Thirty kilograms of water warms by 15 K. Q = 30×4200×15 = 1.89×10⁶ J. This is energy gained by water, not necessarily total solar energy incident on the collector.

Find specific heat

A 0.50 kg block receives 9.0 kJ and warms by 30 K. c = Q/(mΔT) = 9000/(0.50×30) = 600 J kg⁻¹K⁻¹.

Laboratory evidence

Measure specific heat by electrical heating

Measure heater voltage V, current I, heating time t, block mass m and temperature rise ΔT. The simplest model equates VIt = mcΔT, so c = VIt/(mΔT). Insulate the block, ensure good heater and thermometer contact, and use teacher-approved low-voltage apparatus.

Energy also warms the heater, sensor and insulation and escapes to surroundings. A temperature–time graph can help estimate cooling; a non-linear rise indicates changing loss rate. Repeat readings and report uncertainty rather than copying a reference value to excessive precision.

Measurement	Common issue	Improvement
Temperature	Sensor lag or poor contact	Thermal paste where approved; wait consistently
Electrical energy	Voltage/current variation	Monitor both during heating
Mass	Wrong object boundary	State whether heater/sensor are included
Heat loss	c calculated too high or low by model	Insulate and model loss direction

Problem-solving routine

Seven steps for every thermal-energy question

Define system and surroundings.
List masses, initial states and phases.
Predict energy-transfer direction.
Split the path into temperature and phase-change stages.
Choose Q = mcΔT, Q = CΔT or Q = mL.
Apply conservation with one sign convention.
Check final temperature, energy unit and physical range.

Common failures include calling heat “stored,” using Celsius absolute values instead of intervals, omitting a calorimeter, mixing grams with kilograms and accepting a final temperature outside the initial range without an external source. Review Heat & Temperature Study Guide for a wider thermal map.

For online or physical NEB tuition, call 9846662070 with the energy ledger from a problem you attempted.

Practice tasks

Closed-book Quantity of Heat checkpoint

Distinguish heat, temperature and internal energy.
Compare specific heat and heat capacity.
Calculate Q for a 2 kg sample warming 30 K.
Set up an ideal hot-metal/cold-water mixture.
Draw a heating curve with two phase changes.
Build a three-stage ice-to-water calculation.
Evaluate one electrical-heating uncertainty.
Explain why final mixture temperature must pass a range check.

Use PhET Energy Forms and Changes only after making a prediction. Record prediction, observation and energy-boundary explanation.

Frequently asked questions

Questions about Quantity of Heat

Is heat stored inside an object?

In precise thermodynamic language, internal energy is stored; heat is energy transferred across a boundary because of temperature difference.

When can I use Q = mcΔT?

Use it for a temperature change within one phase when specific heat can be treated as constant and the relevant system is defined.

Why is temperature constant during melting?

In the ideal phase-change model, transferred energy changes molecular arrangement rather than average kinetic energy.

What is the difference between c and C?

Specific heat c is per unit mass in J kg−1 K−1; heat capacity C=mc belongs to the whole object in J K−1.

How do I choose calorimetry signs?

Predict heat direction first, take heat into a body as positive or use magnitudes lost=gained, and apply the convention consistently.

Where can I get NEB Quantity of Heat help?

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 Quantity of Heat Study Guide for spaced revision and mixed practice. Curriculum scope and sources were checked on 2 August 2026; follow current CDC, NEB and college instructions if requirements change.

Prerequisite connection

Use units as a model check

The Physical Quantities guide helps verify that mcΔT produces joules and that specific heat carries J kg⁻¹K⁻¹. A correct dimension cannot prove the thermal model is appropriate, but a wrong dimension immediately exposes a missing mass, interval or phase term.

Continue planning