Internal energy is a fundamental concept in physics, particularly within thermodynamics. It represents the total energy contained within a system, encompassing both the kinetic and potential energies of its molecules. For students studying the AS & A Level Physics curriculum (9702), grasping the nuances of internal energy is crucial for understanding various physical phenomena and applications. This article delves into the comprehensive aspects of internal energy, providing detailed explanations, theoretical frameworks, and practical examples to facilitate a thorough comprehension of the subject.

Key Concepts

Definition of Internal Energy

Internal energy, often denoted as $ U $, is the total energy associated with the microscopic components of a system. It includes both kinetic energy, arising from the motion of molecules, and potential energy, stemming from the interactions between molecules. Mathematically, it can be expressed as: $$ U = K + V $$ where $ K $ is the total kinetic energy and $ V $ is the total potential energy of the system.

Kinetic Energy of Molecules

The kinetic energy ($ K $) of molecules in a system arises from their motion, which includes translational, rotational, and vibrational movements. For an ideal gas, the kinetic energy is primarily translational and can be calculated using the equation: $$ K = \frac{3}{2} nRT $$ where $ n $ is the number of moles, $ R $ is the universal gas constant, and $ T $ is the temperature in Kelvin. This relationship underscores the direct proportionality between kinetic energy and temperature.

Potential Energy of Molecules

Potential energy ($ V $) in a system is associated with the positions and interactions between molecules. It encompasses various forms such as gravitational, electrical, and chemical potential energy. In the context of thermodynamics, especially within ideal gases, potential energy is often negligible compared to kinetic energy. However, in real gases and condensed phases like liquids and solids, molecular interactions significantly contribute to the total internal energy.

Total Internal Energy

The total internal energy ($ U $) of a system is the sum of its kinetic and potential energies. For an ideal gas, where intermolecular forces are minimal, the internal energy is predominantly kinetic. However, for real gases and other states of matter, both kinetic and potential energies play pivotal roles. The internal energy is a state function, meaning it depends solely on the current state of the system (e.g., temperature, pressure, volume) and not on the path taken to reach that state.

First Law of Thermodynamics

The first law of thermodynamics, also known as the law of energy conservation, states that the change in internal energy ($ \Delta U $) of a closed system is equal to the heat ($ Q $) added to the system minus the work ($ W $) done by the system: $$ \Delta U = Q - W $$ This principle establishes that energy cannot be created or destroyed, only transformed from one form to another.

Heat Capacity and Internal Energy

Heat capacity is a measure of the amount of heat required to change the temperature of a substance. It is directly related to the internal energy of the system. There are two primary types of heat capacities:

Constant Volume Heat Capacity ($ C_V $): The heat capacity measured when the volume of the system remains constant. It is given by: $$ C_V = \left( \frac{\partial U}{\partial T} \right)_V $$
Constant Pressure Heat Capacity ($ C_P $): The heat capacity measured when the pressure of the system remains constant. It is related to $ C_V $ by: $$ C_P = C_V + nR $$ where $ n $ is the number of moles and $ R $ is the gas constant.

Molar Internal Energy

Molar internal energy refers to the internal energy per mole of a substance. It provides a standardized measure, allowing for comparisons between different substances. For an ideal monatomic gas, the molar internal energy is: $$ U = \frac{3}{2} RT $$ where $ R $ is the gas constant and $ T $ is the temperature in Kelvin.

Dependence on Molecular Structure

The internal energy of a substance is significantly influenced by its molecular structure. Different molecular configurations (e.g., diatomic, polyatomic) possess varying degrees of freedom, affecting both kinetic and potential energies. For instance, diatomic molecules have rotational and vibrational modes that contribute to their internal energy, unlike monatomic gases which only have translational kinetic energy.

Internal Energy in Phase Changes

During phase transitions, such as from solid to liquid or liquid to gas, the internal energy changes without a corresponding change in temperature. This is due to the absorption or release of latent heat, which affects the potential energy component as molecules rearrange themselves. For example, melting involves an increase in potential energy as intermolecular bonds weaken.

Measurement of Internal Energy

Internal energy is typically measured using calorimetry, where the heat exchanged in chemical reactions or physical changes is quantified. Indirect methods, such as applying the first law of thermodynamics, are also employed to calculate changes in internal energy based on known quantities of heat and work.

Applications of Internal Energy

Understanding internal energy is crucial for various applications, including:

Thermodynamic Cycles: Analyzing engines and refrigerators relies on internal energy changes to determine efficiency.
Chemical Reactions: Predicting energy changes during reactions involves assessing the internal energy of reactants and products.
Phase Equilibria: Determining conditions for phase transitions depends on internal energy considerations.

Advanced Concepts

Statistical Mechanics and Internal Energy

Statistical mechanics provides a microscopic interpretation of internal energy by considering the distribution of molecular energies. The internal energy can be derived from the partition function ($ Z $), which encapsulates all possible states of the system: $$ U = -\frac{\partial \ln Z}{\partial \beta} $$ where $ \beta = \frac{1}{k_B T} $ and $ k_B $ is Boltzmann's constant. This approach links macroscopic thermodynamic quantities to the underlying molecular behavior.

Internal Energy in Non-Ideal Systems

In real (non-ideal) systems, intermolecular forces play a significant role in determining internal energy. The potential energy component becomes more substantial, and deviations from ideal gas behavior must be accounted for using equations of state like the Van der Waals equation: $$ \left( P + \frac{a n^2}{V^2} \right) (V - nb) = nRT $$ where $ a $ and $ b $ are constants specific to each gas, representing intermolecular attractions and the finite size of molecules, respectively.

Heat Flow and Internal Energy Transfer

Heat flow within a system is a manifestation of internal energy transfer. Conduction, convection, and radiation are the primary modes through which heat energy is distributed, affecting the internal energy distribution. Understanding these mechanisms is essential for applications in thermal management and engineering.

Entropy and Internal Energy

Entropy ($ S $) is a measure of the disorder within a system. The relationship between entropy and internal energy is captured by the second law of thermodynamics, which states that the total entropy of an isolated system can never decrease over time. The interplay between internal energy and entropy is crucial for understanding spontaneous processes and the directionality of energy transfer.

Thermodynamic Potentials

Thermodynamic potentials, such as Helmholtz free energy ($ F $) and Gibbs free energy ($ G $), are functions derived from internal energy and other state variables. They are instrumental in predicting the spontaneity of processes and phase transitions. For example, Helmholtz free energy is given by: $$ F = U - TS $$ where $ T $ is temperature and $ S $ is entropy.

Quantum Mechanical Perspective

From a quantum mechanical viewpoint, internal energy encompasses the energy levels of electrons, vibrational modes, and rotational states of molecules. Quantum statistics, such as Bose-Einstein and Fermi-Dirac distributions, describe the occupancy of these energy levels, influencing the internal energy calculations at microscopic scales.

Temperature Dependence of Internal Energy

Internal energy is intrinsically linked to temperature. For an ideal gas, the internal energy increases linearly with temperature, as observed in the equation: $$ U = \frac{3}{2} nRT $$ In more complex systems, the relationship can be nonlinear due to factors like phase changes and varying degrees of freedom.

Internal Energy and Chemical Potential

Chemical potential ($ \mu $) is the change in internal energy with respect to the number of particles at constant entropy and volume: $$ \mu = \left( \frac{\partial U}{\partial N} \right)_{S,V} $$ This concept is vital in chemical thermodynamics, determining the direction of chemical reactions and phase equilibria.

Internal Energy in Open Systems

While internal energy is typically discussed in the context of closed systems, open systems exchange both energy and matter with their surroundings. The first law of thermodynamics for open systems incorporates these exchanges, allowing for the calculation of internal energy changes in processes like chemical reactions in reactors.

Advanced Problem-Solving: Calculating Internal Energy Changes

Consider a scenario where 2 moles of an ideal monatomic gas are heated from 300 K to 500 K at constant volume. Calculate the change in internal energy.

Using the formula for internal energy of an ideal gas: $$ \Delta U = n C_V \Delta T $$ For a monatomic ideal gas, $ C_V = \frac{3}{2} R $. Thus, $$ \Delta U = 2 \times \frac{3}{2} R \times (500 - 300) = 3R \times 200 = 600R $$ If $ R = 8.314 \, \text{J/mol.K} $, then: $$ \Delta U = 600 \times 8.314 = 4988.4 \, \text{J} $$ Therefore, the internal energy increases by approximately 4988.4 J.

Interdisciplinary Connections: Internal Energy in Chemistry and Engineering

Internal energy is not confined to physics; it plays a pivotal role in chemistry and engineering. In chemistry, it helps in understanding reaction energetics, bond formation, and breaking. In engineering, especially in thermal and mechanical systems, internal energy calculations are essential for designing efficient engines, refrigeration systems, and HVAC (Heating, Ventilation, and Air Conditioning) systems. For instance, the efficiency of a heat engine is determined by how effectively it can convert internal energy changes into useful work.

Comparison Table

Aspect	Internal Energy	Enthalpy
Definition	Sum of kinetic and potential energies of molecules in a system.	Total heat content; $ H = U + PV $.
Dependence	Depends on the state variables: temperature, volume, and internal forces.	Depends on internal energy and $ PV $ work.
Measurement	Measured using calorimetry and applying the first law of thermodynamics.	Measured by accounting for heat at constant pressure conditions.
Applications	Used in calculating heat transfer, work done, and energy changes in systems.	Used in processes occurring at constant pressure, such as chemical reactions.
Mathematical Relation	$ U = K + V $	$ H = U + PV $

Summary and Key Takeaways

Internal energy comprises the total kinetic and potential energies of molecules within a system.
It is a state function dependent on temperature, volume, and intermolecular forces.
The first law of thermodynamics relates changes in internal energy to heat and work.
Advanced studies link internal energy to statistical mechanics, quantum theory, and interdisciplinary applications.
Understanding internal energy is essential for analyzing thermodynamic processes and real-world applications in physics, chemistry, and engineering.

Examiner Tip

Tips

Remember the acronym "Kinetic Plus Potential Equals Internal" to easily recall that internal energy is the sum of kinetic and potential energies. Use the formula $ \Delta U = Q - W $ as a checklist to ensure you account for all energy transfers in a system. Practice problem-solving with real-life scenarios, such as heating gases in different containers, to strengthen your understanding and prepare effectively for exams.

Did You Know

Did you know that the concept of internal energy dates back to the early studies of thermodynamics in the 19th century? One fascinating application is in understanding the energy transformations within the Earth's mantle, which drive plate tectonics. Additionally, internal energy plays a crucial role in modern technologies like superconductors and quantum computing, where precise energy management at the molecular level is essential for performance.

Common Mistakes

Incorrect Application of the First Law: Students often forget to account for work done when applying the first law of thermodynamics, leading to incomplete calculations of internal energy changes.
Confusing Internal Energy with Enthalpy: Mixing up internal energy ($ U $) with enthalpy ($ H $) can result in errors, especially when dealing with processes at constant pressure.
Ignoring Degrees of Freedom: Overlooking the different degrees of freedom in molecules when calculating kinetic energy can lead to inaccurate internal energy values.

FAQ

What is internal energy?

Internal energy is the total energy contained within a system, encompassing both the kinetic and potential energies of its molecules.

How does temperature affect internal energy?

Temperature is directly proportional to the kinetic energy of molecules, so as temperature increases, the internal energy of the system also increases.

What is the difference between internal energy and enthalpy?

Internal energy ($ U $) is the total energy within a system, while enthalpy ($ H $) is the sum of internal energy and the product of pressure and volume ($ H = U + PV $).

Can internal energy change without a temperature change?

Yes, during phase changes, such as melting or boiling, internal energy changes due to alterations in potential energy without a corresponding temperature change.

How is internal energy measured in experiments?

Internal energy changes are typically measured using calorimetry, where the heat exchanged in reactions or physical changes is quantified.

What role does internal energy play in the first law of thermodynamics?

The first law of thermodynamics states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system ($ \Delta U = Q - W $).

1. Capacitance

1.1 Energy Stored in a Capacitor

1.1.1 Determine electric potential energy stored in a capacitor from the area under the potential–charge g

1.1.2 Recall and use W = ½QV = ½CV²

1.2 Discharging a Capacitor

1.2.1 Analyze graphs of potential difference, charge, and current during capacitor discharge

1.2.2 Recall and use τ = RC for the time constant during discharge

1.2.3 Use equations of the form x = x₀e^(-t / RC) for current, charge, or potential during discharge

1.3 Capacitors and Capacitance

1.3.1 Define capacitance for isolated spherical conductors and parallel plate capacitors

1.3.2 Recall and use C = Q / V

1.3.3 Derive formulae for combined capacitance of capacitors in series and parallel

1.3.4 Use capacitance formulae for capacitors in series and parallel

2. Nuclear Physics

2.1 Mass Defect and Nuclear Binding Energy

2.1.1 Sketch the variation of binding energy per nucleon with nucleon number

2.1.2 Explain nuclear fusion and nuclear fission

2.1.3 Calculate the energy released in nuclear reactions using E = c²∆m

2.1.4 Understand the equivalence between energy and mass (E = mc²)

2.1.5 Define and use the terms mass defect and binding energy

2.2 Radioactive Decay

2.2.1 Understand that fluctuations in count rate provide evidence for random decay

2.2.2 Understand that radioactive decay is spontaneous and random

2.2.3 Define activity and decay constant, and recall A = λN

2.2.4 Define half-life

2.2.5 Use λ = 0.693 / t₁/₂ for the half-life relationship

2.2.6 Understand exponential decay and use the relationship x = x₀e^(-λt)

3. Kinematics

3.1 Equations of Motion

3.1.1 Define and use distance, displacement, speed, velocity, acceleration

3.1.2 Use graphical methods to represent motion

3.1.3 Determine displacement from velocity–time graph

3.1.4 Determine velocity using gradient of displacement–time graph

3.1.5 Determine acceleration using gradient of velocity–time graph

3.1.6 Derive equations for uniformly accelerated motion

3.1.7 Solve problems of uniformly accelerated motion

3.1.8 Describe experiment to determine acceleration due to gravity

3.1.9 Explain motion with uniform velocity and perpendicular acceleration

4. Deformation of Solids

4.1 Stress and Strain

4.1.1 Understand and use the terms load, extension, compression, and limit of proportionality

4.1.2 Recall and use Hooke’s law

4.1.3 Recall and use the formula for spring constant k = F / x

4.1.4 Define and use terms stress, strain, and Young's modulus

4.1.5 Describe an experiment to determine Young’s modulus

4.1.6 Understand deformation caused by tensile or compressive forces

4.2 Elastic and Plastic Behaviour

4.2.1 Understand elastic and plastic deformation and elastic limit

4.2.2 Understand area under the force–extension graph as work done

4.2.3 Calculate elastic potential energy using EP = ½kx²

5. Gravitational Fields

5.1 Gravitational Field of a Point Mass

5.1.1 Understand that g is approximately constant for small height changes near Earth's surface

5.1.2 Recall and use g = GM / r²

5.1.3 Derive and use g = GM / r² for gravitational field strength

5.2 Gravitational Potential

5.2.1 Define gravitational potential as work done per unit mass in bringing a test mass from infinity

5.2.2 Use ϕ = -GM / r for gravitational potential due to a point mass

5.2.3 Use EP = -GMm / r for gravitational potential energy between two point masses

5.3 Gravitational Field

5.3.1 Define gravitational field as force per unit mass

5.3.2 Represent a gravitational field using field lines

5.4 Gravitational Force Between Point Masses

5.4.1 For point outside uniform sphere, treat mass as a point mass at its center

5.4.2 Analyze circular orbits in gravitational fields

5.4.3 Recall and use Newton's law of gravitation F = Gm₁m₂ / r²

6. Electricity

6.1 Resistance and Resistivity

6.1.1 Understand that the resistance of a thermistor decreases as temperature increases

6.1.2 Define resistance and recall and use V = IR

6.1.3 Sketch I–V characteristics for metallic conductor, semiconductor diode, and filament lamp

6.1.4 Explain that the resistance of a filament lamp increases as current increases

6.1.5 State Ohm’s law and recall and use R = ρL / A

6.1.6 Understand that the resistance of an LDR decreases as light intensity increases

6.2 Electric Current

6.2.1 Understand that an electric current is a flow of charge carriers

6.2.2 Understand that the charge on charge carriers is quantised

6.2.3 Recall and use Q = It

6.2.4 Use I = Anvq for current-carrying conductors

6.3 Potential Difference and Power

6.3.1 Define potential difference as energy transferred per unit charge

6.3.2 Recall and use V = W / Q

6.3.3 Recall and use P = VI, P = I²R, P = V² / R

7. D.C. Circuits

7.1 Practical Circuits

7.1.1 Recall and use the circuit symbols in the syllabus

7.1.2 Draw and interpret circuit diagrams using circuit symbols

7.1.3 Define electromotive force (e.m.f.) of a source as energy transferred per unit charge

7.1.4 Distinguish between e.m.f. and potential difference (p.d.)

7.1.5 Understand the effects of internal resistance on terminal potential difference

7.2 Kirchhoff’s Laws

7.2.1 Recall Kirchhoff’s first law: conservation of charge

7.2.2 Recall Kirchhoff’s second law: conservation of energy

7.2.3 Derive the formula for combined resistance of resistors in series using Kirchhoff’s laws

7.2.4 Use the formula for combined resistance of resistors in series

7.2.5 Derive the formula for combined resistance of resistors in parallel using Kirchhoff’s laws

7.2.6 Use the formula for combined resistance of resistors in parallel

7.2.7 Use Kirchhoff’s laws to solve simple circuit problems

7.3 Potential Dividers

7.3.1 Understand the principle of a potential divider circuit

7.3.2 Recall and use the principle of the potentiometer for comparing potential differences

7.3.3 Understand the use of a galvanometer in null methods

7.3.4 Explain the use of thermistors and LDRs in potential dividers to provide a potential dependent on te

8. Thermal Equilibrium

8.1 Thermal Energy Transfer

8.1.1 Understand that thermal energy transfers from higher to lower temperature

8.1.2 Understand that regions of equal temperature are in thermal equilibrium

9. Temperature Scales

9.1 Temperature Measurement

9.1.1 Understand physical properties that vary with temperature (e.g., density, gas volume, resistance)

9.1.2 Convert temperatures between Kelvin and Celsius, and recall T(K) = θ(°C) + 273.15

10. Magnetic Fields

10.1 Concept of a Magnetic Field

10.1.1 Understand that a magnetic field is a field of force produced by moving charges or permanent magnets

10.1.2 Represent a magnetic field using field lines

10.2 Force on a Current-Carrying Conductor

10.2.1 Understand that a force acts on a current-carrying conductor in a magnetic field

10.2.2 Recall and use F = BIL sin θ for the force on a current-carrying conductor in a magnetic field

10.2.3 Define magnetic flux density as the force per unit current per unit length on a wire at right angles

10.3 Force on a Moving Charge

10.3.1 Determine the direction of the force on a charge moving in a magnetic field

10.3.2 Recall and use F = BQv sin θ for the force on a moving charge in a magnetic field

10.3.3 Understand the origin of the Hall voltage and use the expression VH = BI / (ntq) for the Hall voltag

10.3.4 Understand the use of a Hall probe to measure magnetic flux density

10.4 Magnetic Fields Due to Currents

10.4.1 Sketch magnetic field patterns due to currents in a straight wire, flat coil, and solenoid

10.4.2 Understand that magnetic field in a solenoid is increased by a ferrous core

10.4.3 Explain the origin of forces between current-carrying conductors and determine the direction of the

10.5 Electromagnetic Induction

10.5.1 Define magnetic flux as the product of magnetic flux density and area perpendicular to flux directio

10.5.2 Recall and use Φ = BA for magnetic flux

10.5.3 Understand and use the concept of magnetic flux linkage

10.5.4 Explain experiments that show changing magnetic flux induces an e.m.f.

10.5.5 Recall and use Faraday’s and Lenz’s laws of electromagnetic induction

11. Specific Heat Capacity and Latent Heat

11.1 Specific Heat Capacity

11.1.1 Define and use specific heat capacity

11.2 Latent Heat

11.2.1 Define and use specific latent heat; distinguish between fusion and vaporisation

12. Dynamics

12.1 Momentum and Newton’s Laws of Motion

12.1.1 Mass resists change in motion

12.1.2 Recall F = ma and solve related problems

12.1.3 Define and use linear momentum

12.1.4 Force as rate of change of momentum

12.1.5 State and apply Newton’s laws

12.1.6 Describe weight as effect of gravitational field

12.1.7 Weight of an object is mass × gravitational acceleration

12.2 Non-uniform Motion

12.2.1 Understand frictional and drag forces

12.2.2 Describe motion in uniform gravitational field with air resistance

12.2.3 Objects moving against resistive force may reach terminal velocity

12.3 Linear Momentum and its Conservation

12.3.1 State conservation of momentum

12.3.2 Apply conservation of momentum to solve problems

12.3.3 For elastic collision, kinetic energy and relative speed are conserved

12.3.4 Momentum is conserved, but some kinetic energy may change

13. Medical Physics

13.1 Production and Use of Ultrasound

13.1.1 Understand that a piezo-electric crystal changes shape when a p.d. is applied and generates an e.m.f

13.1.2 Understand how ultrasound waves are generated and detected by a piezoelectric transducer

13.1.3 Understand how ultrasound reflection at boundaries provides diagnostic information about internal st

13.1.4 Define specific acoustic impedance as Z = ρc

13.1.5 Use the equation IR / I₀ = (Z₁ – Z₂)² / (Z₁ + Z₂)² for the intensity reflection coefficient

13.2 Production and Use of X-rays

13.2.1 Explain that X-rays are produced by electron bombardment of a metal target and calculate the minimum

13.2.2 Understand the use of X-rays in imaging internal body structures and the term 'contrast' in X-ray im

13.2.3 Recall and use I = I₀e^(-μx) for the attenuation of X-rays in matter

13.2.4 Understand how computed tomography (CT) produces 3D images by combining multiple 2D X-ray images

13.3 PET Scanning

13.3.1 Understand that a tracer contains radioactive nuclei and is introduced into the body for imaging

13.3.2 Understand that β+ decay is used in positron emission tomography (PET)

13.3.3 Understand that annihilation occurs when a particle interacts with its antiparticle, conserving mass

13.3.4 Explain how gamma-ray photons from annihilation are detected to create an image of tracer concentrat

14. Waves

14.1 Progressive Waves

14.1.1 Describe wave motion in ropes, springs, and ripple tanks

14.1.2 Understand and use the terms displacement, amplitude, phase difference, period, frequency, wavelengt

14.1.3 Use time-base and y-gain on a cathode-ray oscilloscope (CRO) to determine frequency and amplitude

14.1.4 Derive and use v = f λ for the wave equation

14.1.5 Recall and use v = f λ

14.1.6 Understand energy transfer by a progressive wave

14.1.7 Recall and use intensity = power / area, intensity ∝ (amplitude)²

14.2 Transverse and Longitudinal Waves

14.2.1 Compare transverse and longitudinal waves

14.2.2 Analyze and interpret graphical representations of transverse and longitudinal waves

14.3 Doppler Effect for Sound Waves

14.3.1 Understand the change in frequency when a sound source moves relative to a stationary observer

14.3.2 Use the expression f₀ = fₛ(v / (v ± vₛ)) for the observed frequency

14.4 Electromagnetic Spectrum

14.4.1 State all electromagnetic waves are transverse waves traveling at the same speed in free space

14.4.2 Recall the range of wavelengths from radio waves to γ-rays

14.4.3 Recall that wavelengths 400–700 nm are visible to the human eye

14.5 Polarisation

14.5.1 Understand that polarisation is a phenomenon associated with transverse waves

14.5.2 Recall and use Malus's law (I = I₀ cos²θ) to calculate intensity of a plane-polarised wave after pas

15. The Mole

15.1 The Mole

15.1.1 Understand that amount of substance is an SI base quantity with the unit mol

15.1.2 Use molar quantities where one mole contains Avogadro's constant of particles

16. Equation of State

16.1 Ideal Gas Law

16.1.1 Understand that a gas obeying pV ∝ T is an ideal gas

16.1.2 Recall and use the equation pV = nRT for an ideal gas

16.1.3 Recall pV = NkT, where N = number of molecules and k is Boltzmann constant

16.1.4 Use the relationship k = R / NA

17. Kinetic Theory of Gases

17.1 Kinetic Theory

17.1.1 State the basic assumptions of the kinetic theory of gases

17.1.2 Explain pressure exerted by a gas due to molecular movement

17.1.3 Derive and use pV = (3/2)NmkT for pressure of a gas

17.1.4 Compare pV = (3/2)NmkT with pV = NkT to deduce average kinetic energy of a molecule

18. Particle Physics

18.1 Atoms, Nuclei and Radiation

18.1.1 Infer the existence and small size of the nucleus from α-particle scattering

18.1.2 Describe the nuclear atom model: protons, neutrons, and electrons

18.1.3 Distinguish between nucleon number and proton number

18.1.4 Understand isotopes as forms of the same element with different neutrons

18.1.5 Use the notation AZX for nuclides representation

18.1.6 Understand conservation of nucleon number and charge in nuclear processes

18.1.7 Describe the composition, mass, and charge of α-, β-, and γ-radiations

18.1.8 Understand antiparticles and positrons as antiparticles of electrons

18.1.9 State that (electron) antineutrinos are produced during β- decay and neutrinos during β+ decay

18.1.10 Represent α- and β-decay using radioactive decay equations

18.1.11 Use unified atomic mass unit (u) for mass

18.2 Fundamental Particles

18.2.1 Understand quarks as fundamental particles with six flavours

18.2.2 Understand hadrons as baryons (three quarks) or mesons (one quark and one antiquark)

18.2.3 Describe changes in quark composition during β- and β+ decay

18.2.4 Describe protons and neutrons as composed of quarks

18.2.5 Recall and use the charge of each quark and its respective antiquark

18.2.6 Recall electrons and neutrinos as fundamental particles (leptons)

19. Internal Energy

19.1 Internal Energy

19.1.1 Understand that internal energy is the sum of kinetic and potential energies of molecules in a syste

19.1.2 Relate rise in temperature to an increase in internal energy

20. Forces, Density and Pressure

20.1 Turning Effects of Forces

20.1.1 Weight acts at a single point: centre of gravity

20.1.2 Define and apply the moment of a force

20.1.3 Understand the concept of a couple

20.1.4 Define and apply torque of a couple

20.2 Equilibrium of Forces

20.2.1 State and apply the principle of moments

20.2.2 System in equilibrium has no resultant force or torque

20.2.3 Use a vector triangle to represent coplanar forces in equilibrium

20.3 Density and Pressure

20.3.1 Define and use density

20.3.2 Define and use pressure

20.3.3 Derive equation for hydrostatic pressure ∆p = ρg∆h

20.3.4 Use the equation ∆p = ρg∆h

20.3.5 Understand upthrust as the effect of hydrostatic pressure

20.3.6 Calculate upthrust using F = ρgV (Archimedes' principle)

21. Astronomy and Cosmology

21.1 Standard Candles

21.1.1 Understand luminosity as the total power radiated by a star

21.1.2 Recall and use the inverse square law F = L / (4πd²) for radiant flux intensity

21.1.3 Understand that an object with known luminosity is a standard candle

21.1.4 Use standard candles to determine distances to galaxies

21.2 Stellar Radii

21.2.1 Recall and use Wien’s displacement law λmax ∝ 1 / T to estimate the surface temperature of a star

21.2.2 Use Stefan–Boltzmann law L = 4πσr²T⁴

21.2.3 Use Wien’s law and Stefan–Boltzmann law to estimate the radius of a star

21.3 Hubble’s Law and Big Bang Theory

21.3.1 Understand redshift and the increase in wavelength of light from distant objects

21.3.2 Use ∆λ / λ = ∆f / f = v / c for redshift

21.3.3 Explain why redshift suggests the Universe is expanding

21.3.4 Recall and use Hubble’s law v = H₀d to explain the Big Bang theory

22. First Law of Thermodynamics

22.1 First Law

22.1.1 Recall and use W = p∆V for work done when the volume of a gas changes at constant pressure

22.1.2 Understand the difference between work done by a gas and work done on a gas

22.1.3 Recall and use the first law of thermodynamics: ∆U = q + W

23. Alternating Currents

23.1 Characteristics of Alternating Currents

23.1.1 Understand and use terms period, frequency, and peak value for alternating current or voltage

23.1.2 Use x = x₀ sin(ωt) for sinusoidal alternating current or voltage

23.1.3 Recall that the mean power in a resistive load is half the maximum power for sinusoidal current

23.1.4 Distinguish between root-mean-square (r.m.s.) and peak values and recall I₀r.m.s = I₀ / √2 and V₀r.m

23.2 Rectification and Smoothing

23.2.1 Distinguish graphically between half-wave and full-wave rectification

23.2.2 Explain the use of a single diode for half-wave rectification

23.2.3 Explain the use of four diodes (bridge rectifier) for full-wave rectification

23.2.4 Analyze the effect of a capacitor in smoothing, including the effect of capacitance and load resista

24. Superposition

24.1 Stationary Waves

24.1.1 Explain and use the principle of superposition

24.1.2 Understand experiments demonstrating stationary waves using microwaves, stretched strings, and air c

24.1.3 Explain the formation of stationary waves using graphical methods and identify nodes and antinodes

24.1.4 Determine wavelength from the positions of nodes or antinodes

24.2 Diffraction

24.2.1 Explain diffraction and show understanding of related experiments

24.2.2 Understand the effect of gap width relative to wavelength in diffraction experiments

24.3 Interference

24.3.1 Understand the terms interference and coherence

24.3.2 Demonstrate two-source interference using water waves, sound, light, and microwaves

24.3.3 Understand the conditions required for two-source interference fringes

24.3.4 Recall and use λ = ax / D for double-slit interference with light

24.4 Diffraction Grating

24.4.1 Recall and use d sin θ = nλ for diffraction grating calculations

24.4.2 Describe the use of a diffraction grating to determine the wavelength of light

25. Simple Harmonic Oscillations

25.1 Simple Harmonic Motion

25.1.1 Understand and use terms displacement, amplitude, period, frequency, angular frequency, and phase di

25.1.2 Understand that simple harmonic motion occurs when acceleration is proportional to displacement from

25.1.3 Use a = -ω²x and recall x = x₀ sin(ωt) as the solution

25.1.4 Use v = v₀ cos(ωt) and v = ±ω√(x₀² - x²) for velocity

26. Energy in Simple Harmonic Motion

26.1 Energy in SHM

26.1.1 Describe the interchange between kinetic and potential energy during SHM

26.1.2 Recall and use E = ½mω²x₀² for the total energy of a system undergoing SHM

27. Quantum Physics

27.1 Energy and Momentum of a Photon

27.1.1 Understand that electromagnetic radiation has a particulate nature

27.1.2 Recall and use E = hf for the energy of a photon

27.1.3 Use the electronvolt (eV) as a unit of energy

27.1.4 Understand that a photon has momentum and use p = E / c for photon momentum

27.2 Photoelectric Effect

27.2.1 Understand that photoelectrons are emitted from a metal surface when illuminated by electromagnetic

27.2.2 Understand and use the terms threshold frequency and threshold wavelength

27.2.3 Explain photoelectric emission in terms of photon energy and work function

27.2.4 Recall and use hf = Φ + ½mv² for the maximum kinetic energy of photoelectrons

27.2.5 Explain why the maximum kinetic energy of photoelectrons is independent of intensity, while current

27.3 Wave-Particle Duality

27.3.1 Understand that the photoelectric effect shows the particulate nature of light, while diffraction sh

27.3.2 Describe and interpret electron diffraction as evidence for the wave nature of particles

27.3.3 Understand the de Broglie wavelength as the wavelength associated with a moving particle

27.3.4 Recall and use λ = h / p for de Broglie wavelength

27.4 Energy Levels in Atoms and Line Spectra

27.4.1 Understand discrete electron energy levels in atoms (e.g., atomic hydrogen)

27.4.2 Understand the appearance and formation of emission and absorption line spectra

27.4.3 Recall and use hf = E₁ – E₂ for the energy difference between electron energy levels

28. Damped and Forced Oscillations, Resonance

28.1 Damped Oscillations

28.1.1 Understand that damping occurs due to resistive forces

28.1.2 Understand the types of damping: light, critical, and heavy damping

28.2 Resonance

28.2.1 Understand that resonance occurs when an oscillating system is forced to oscillate at its natural fr

29. Work, Energy and Power

29.1 Energy Conservation

29.1.1 Understand the concept of work, and recall W = F × s

29.1.2 Apply the principle of conservation of energy

29.1.3 Understand efficiency as useful energy output / total energy input

29.1.4 Use efficiency concept to solve problems

29.1.5 Define power as work done per unit time

29.1.6 Solve problems using P = W / t

29.1.7 Derive P = Fv and solve problems

29.2 Gravitational Potential Energy and Kinetic Energy

29.2.1 Derive ∆EP = mg∆h for gravitational potential energy changes

29.2.2 Recall and use ∆EP = mg∆h for gravitational potential energy changes

29.2.3 Derive EK = ½mv² for kinetic energy

29.2.4 Recall and use EK = ½mv² for kinetic energy

30. Electric Fields

30.1 Electric Fields and Field Lines

30.1.1 Understand that an electric field is a field of force and define it as force per unit positive charg

30.1.2 Represent an electric field using field lines

30.2 Uniform Electric Fields

30.2.1 Recall and use E = ∆V / ∆d to calculate electric field strength between charged parallel plates

30.2.2 Describe the effect of a uniform electric field on the motion of charged particles

30.3 Electric Force Between Point Charges

30.3.1 Understand that, for a point outside a spherical conductor, the charge may be considered a point mas

30.3.2 Recall and use Coulomb’s law F = Q₁Q₂ / (4πε₀r²) for the force between two point charges

30.4 Electric Field of a Point Charge

30.4.1 Recall and use E = Q / (4πε₀r²) for the electric field strength due to a point charge

30.5 Electric Potential

30.5.1 Define electric potential as work done per unit positive charge in bringing a test charge from infin

30.5.2 Recall and use V = Q / (4πε₀r) for electric potential due to a point charge

30.5.3 Understand how electric potential leads to electric potential energy of two point charges and use EP

31. Physical Quantities and Units

31.1 Physical Quantities

31.1.1 Physical quantities consist of magnitude and unit

31.1.2 Estimate physical quantities from the syllabus

31.2 SI Units

31.2.1 SI base units: mass, length, time, current, temperature

31.2.2 Express derived units from SI base units

31.2.3 Check homogeneity of physical equations

31.2.4 Use prefixes (pico, nano, micro, kilo, etc.)

31.3 Errors and Uncertainties

31.3.1 Understand systematic and random errors

31.3.2 Assess uncertainty in derived quantities

31.4 uniform Electric Fields

31.4.1 Distinguish between precision and accuracy

31.5 Scalars and Vectors

31.5.1 Difference between scalar and vector quantities

31.5.2 Add and subtract coplanar vectors

31.5.3 Represent a vector as components

32. Motion in a Circle

32.1 Centripetal Acceleration

32.1.1 Understand centripetal acceleration and its role in circular motion

32.1.2 Recall and use a = rω² and a = v² / r

32.1.3 Recall and use F = mrω² and F = mv² / r

32.1.4 Understand force causing centripetal acceleration is always perpendicular to motion

32.2 Kinematics of Uniform Circular Motion

32.2.1 Recall and use ω = 2π / T and v = rω

32.2.2 Understand and use angular speed

32.2.3 Define and express angular displacement in radians

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Aspect	Internal Energy	Enthalpy
Definition	Sum of kinetic and potential energies of molecules in a system.	Total heat content; \( H = U + PV \).
Dependence	Depends on the state variables: temperature, volume, and internal forces.	Depends on internal energy and \( PV \) work.
Measurement	Measured using calorimetry and applying the first law of thermodynamics.	Measured by accounting for heat at constant pressure conditions.
Applications	Used in calculating heat transfer, work done, and energy changes in systems.	Used in processes occurring at constant pressure, such as chemical reactions.
Mathematical Relation	\( U = K + V \)	\( H = U + PV \)

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Understanding Internal Energy: Sum of Kinetic and Potential Energies of Molecules in a System

Introduction