Kirchhoff’s Laws are fundamental principles in electrical circuit theory, essential for analyzing complex DC circuits. Named after Gustav Kirchhoff, these laws provide a systematic method to determine unknown currents and voltages within a circuit. For students in the AS & A Level Physics curriculum (9702), mastering Kirchhoff’s Laws is crucial for solving various circuit problems effectively and understanding the underlying principles of electrical engineering and physics.

Key Concepts

Understanding Kirchhoff’s Laws

Kirchhoff’s Laws consist of two main principles: Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL). These laws are indispensable tools for circuit analysis, particularly when dealing with circuits containing multiple loops and junctions.

Kirchhoff’s Current Law (KCL)

Kirchhoff’s Current Law states that the total current entering a junction equals the total current leaving the junction. This principle is a direct consequence of the conservation of electric charge. Mathematically, it can be expressed as:

$$\sum I_{in} = \sum I_{out}$$

Where:

Σ I_in is the sum of currents flowing into the junction.
Σ I_out is the sum of currents flowing out of the junction.

For example, consider a junction where three currents meet: I₁ and I₂ flowing into the junction, and I₃ flowing out. According to KCL:

$$I_1 + I_2 = I_3$$

Kirchhoff’s Voltage Law (KVL)

Kirchhoff’s Voltage Law states that the sum of all electrical potential differences around any closed loop in a circuit is zero. This law is derived from the conservation of energy, indicating that the energy supplied by voltage sources is equal to the energy dissipated by resistors and other circuit elements. Mathematically, it is expressed as:

$$\sum V = 0$$

Where:

Σ V is the sum of voltage gains and drops around the loop.

For instance, in a simple loop containing a battery and two resistors, the sum of the voltage provided by the battery equals the sum of the voltage drops across the resistors:

$$V_{battery} - V_{R1} - V_{R2} = 0$$

Applying Kirchhoff’s Laws to Simple Circuits

To solve simple circuit problems using Kirchhoff’s Laws, follow these steps:

Identify Junctions and Loops: Determine the number of junctions and independent loops within the circuit.
Apply KCL: For each junction, apply Kirchhoff’s Current Law to relate the currents entering and leaving the junction.
Apply KVL: For each independent loop, apply Kirchhoff’s Voltage Law to relate the voltages around the loop.
Solve the Equations: Use the resulting system of equations to solve for the unknown currents and voltages.

Consider a simple circuit with a single loop containing a battery of voltage V and two resistors R₁ and R₂. Applying KVL:

$$V - I R_1 - I R_2 = 0$$

Solving for the current I:

$$I = \frac{V}{R_1 + R_2}$$

Example Problem

**Problem:** A circuit consists of a 12 V battery connected in series with two resistors, R₁ = 4 Ω and R₂ = 6 Ω. Determine the current flowing through the circuit.

**Solution:** Applying KVL:

$$12 V - I \times 4 Ω - I \times 6 Ω = 0$$ $$12 = 10I$$ $$I = \frac{12}{10} = 1.2 A$$

The current flowing through the circuit is 1.2 A.

Superposition Principle in Kirchhoff’s Laws

The superposition principle states that in a linear circuit with multiple sources, the contribution of each source to the current and voltage in the circuit can be analyzed independently and then summed to find the total response. When applying Kirchhoff’s Laws, this principle allows for simplifying the analysis of complex circuits by considering one source at a time.

To apply superposition:

Consider one independent source while turning off all other independent sources (replace voltage sources with short circuits and current sources with open circuits).
Apply Kirchhoff’s Laws to solve for the desired quantities.
Repeat the process for each independent source.
Sum all individual contributions to obtain the total current or voltage.

Node-Voltage Method

The Node-Voltage Method is a systematic approach to applying Kirchhoff’s Current Law. It involves selecting a reference node (ground) and assigning voltages to the other nodes. By expressing KCL at each non-reference node, a system of equations can be formulated and solved for the node voltages, which can then be used to determine the currents in the circuit.

**Steps for Node-Voltage Method:**

Select a Reference Node: Choose one node as the ground with voltage = 0 V.
Assign Node Voltages: Assign voltage variables to the other nodes.
Apply KCL to Each Node: Write KCL equations for each non-reference node using Ohm’s Law to express the currents in terms of node voltages.
Solve the Equations: Solve the system of equations to find the node voltages.
Determine Currents: Use the node voltages to calculate the desired currents using Ohm’s Law.

Thevenin’s and Norton’s Theorems

While not directly Kirchhoff’s Laws, Thevenin’s and Norton’s theorems are complementary techniques for simplifying complex circuits, making Kirchhoff’s analysis more manageable.

Thevenin’s Theorem: Any linear circuit with voltage and current sources can be replaced by an equivalent circuit consisting of a single voltage source (V_th) in series with a resistor (R_th).
Norton’s Theorem: Any linear circuit with voltage and current sources can be replaced by an equivalent circuit consisting of a single current source (I_N) in parallel with a resistor (R_N).

These theorems facilitate the application of Kirchhoff’s Laws by reducing the complexity of the circuit, allowing for easier analysis of specific components or sections within the circuit.

Analysis of Parallel and Series Circuits

Kirchhoff’s Laws are essential for analyzing both parallel and series circuits, which are common configurations in electrical networks.

Series Circuits: In a series circuit, components are connected end-to-end, so the same current flows through each component. KVL is particularly useful for determining voltage drops across each resistor.
Parallel Circuits: In a parallel circuit, components are connected across the same voltage source, so the voltage across each component is equal. KCL is especially useful for finding the current through each branch.

Combining series and parallel configurations in more complex circuits often requires the simultaneous application of both KCL and KVL to solve for unknowns.

Advanced Concepts

Mathematical Derivations of Kirchhoff’s Laws

Delving deeper into Kirchhoff’s Laws involves understanding their mathematical foundations and derivations from fundamental physical principles.

Derivation of Kirchhoff’s Current Law (KCL)

KCL is derived from the conservation of electric charge. At any junction, charge cannot accumulate; hence, the rate at which charge enters must equal the rate at which it leaves. Mathematically:

$$\frac{dQ}{dt}(junction) = 0$$ $$\sum I_{in} - \sum I_{out} = 0$$ $$\sum I_{in} = \sum I_{out}$$

Derivation of Kirchhoff’s Voltage Law (KVL)

KVL is derived from the conservation of energy. As a charge moves around a closed loop, the total energy gained from sources must equal the energy lost in resistive elements. Applying the first law of thermodynamics (conservation of energy) to the loop:

$$\sum V = 0$$

Application of Kirchhoff’s Laws in Complex Circuits

Applying Kirchhoff’s Laws to complex circuits involves dealing with multiple loops and junctions, requiring systematic approaches like matrix methods or linear algebra to solve the resulting system of equations.

Mesh Analysis

Mesh analysis uses KVL to write equations for each independent loop (mesh) in a planar circuit. By assigning mesh currents and applying KVL, a system of equations can be formed and solved for the unknown currents.

**Steps for Mesh Analysis:**

Identify all the meshes in the circuit.
Assign a mesh current to each mesh, typically in a clockwise direction.
Apply KVL to each mesh to form equations based on the voltage drops and rises.
Solve the system of equations to find the mesh currents.

Supermesh Concept

A supermesh is used when a current source is present between two meshes. Instead of writing KVL around each mesh individually, the supermesh combines the two meshes into a single equation, bypassing the current source. An additional equation is then added based on the current source’s value.

Dependent Sources and Kirchhoff’s Laws

Dependent sources are circuit elements whose values depend on other circuit variables, such as voltage or current elsewhere in the circuit. When analyzing circuits with dependent sources using Kirchhoff’s Laws, it’s essential to express these sources in terms of the controlling variables to form accurate equations.

**Example:** A voltage source that is dependent on the current through a resistor can be expressed as:

$$V = k \times I$$

Where k is a constant. This relationship must be incorporated into the KVL or KCL equations accordingly.

Interdisciplinary Connections

Kircuit’s Laws not only apply to electrical circuits but also find applications across various fields of science and engineering. Understanding these laws enhances problem-solving skills in disciplines such as:

Electrical Engineering: Circuit design, signal processing, and power distribution systems rely heavily on Kirchhoff’s Laws for analysis and optimization.
Mechanical Engineering: Analogous principles apply to force and motion in mechanical systems, where equilibrium conditions resemble current and voltage balances.
Chemical Engineering: Mass balance equations in chemical reactors mirror the current and voltage equations in electrical circuits.

Moreover, the mathematical techniques used in Kirchhoff’s circuit analysis, such as matrix operations and linear algebra, are fundamental tools in various scientific computations and simulations.

Advanced Problem Solving Techniques

Beyond basic applications, Kirchhoff’s Laws can be employed in more sophisticated problem-solving scenarios involving transient analysis, AC circuits, and network theorems.

Transient Analysis in RC Circuits

In circuits containing resistors and capacitors (RC circuits), Kirchhoff’s Laws are applied to analyze the transient response when the circuit is subjected to a step input voltage. The differential equations arising from KVL describe the charging and discharging behavior of the capacitor.

$$V(t) = V_0 \left(1 - e^{-\frac{t}{RC}}\right)$$

Where:

V(t) is the voltage across the capacitor at time t.
V₀ is the initial voltage.
R and C are the resistance and capacitance, respectively.

Analysis of AC Circuits

In alternating current (AC) circuits, Kirchhoff’s Laws are extended to incorporate complex impedances representing resistors, capacitors, and inductors. Phasor representations and complex algebra facilitate the application of KCL and KVL in analyzing AC circuits.

$$V = IZ$$

Where:

Z is the complex impedance.
I is the phasor current.
V is the phasor voltage.

Network Theorems Integration

Kircuit’s Laws integrate seamlessly with network theorems like Thevenin’s, Norton’s, and Superposition, enabling the simplification of complex circuits into manageable equivalents. This integration is pivotal for optimizing circuit design and analysis in both theoretical and practical applications.

Comparison Table

Aspect	Kirchhoff’s Current Law (KCL)	Kirchhoff’s Voltage Law (KVL)
Definition	The total current entering a junction equals the total current leaving.	The sum of all voltages around a closed loop is zero.
Based On	Conservation of electric charge.	Conservation of energy.
Mathematical Expression	$$\sum I_{in} = \sum I_{out}$$	$$\sum V = 0$$
Primary Use	Determining unknown currents at junctions.	Calculating unknown voltages in loops.
Application Example	Finding currents entering and leaving a node with multiple branches.	Calculating voltage drops across resistors in a complex loop.
Relevant Techniques	Node-Voltage Method, Current Division.	Mesh Analysis, Kirchhoff’s Loop Rule.

Summary and Key Takeaways

Kirchhoff’s Current Law (KCL) and Voltage Law (KVL) are essential for analyzing complex electrical circuits.
KCL is based on the conservation of electric charge, while KVL relies on the conservation of energy.
Systematic application of Kirchhoff’s Laws enables the determination of unknown currents and voltages in circuits.
Advanced techniques like mesh analysis and node-voltage method enhance the effectiveness of Kirchhoff’s Laws in complex scenarios.
Understanding Kirchhoff’s Laws is foundational for interdisciplinary applications in engineering and physical sciences.

Examiner Tip

Tips

Use the mnemonic "Lame Current" for KCL (Loops and Monitors Currents) and "Land Electricity" for KVL (Loops and Voltages). Always double-check the direction of assumed currents and the polarity of voltage sources. Practice consistently with different circuit configurations to build confidence and accuracy in applying Kirchhoff’s Laws during exams.

Did You Know

Gustav Kirchhoff, after whom Kirchhoff’s Laws are named, originally developed these laws to explain the spectral lines of light. Additionally, Kirchhoff's Laws are not only applicable to electrical circuits but also to fluid dynamics and thermal systems, showcasing their versatility across different scientific disciplines.

Common Mistakes

Students often confuse KCL and KVL, applying them interchangeably. Another frequent error is neglecting to assign correct polarities to voltage drops, leading to incorrect KVL equations. Additionally, overlooking the need to consider all elements in a loop or junction can result in incomplete or inaccurate solutions.

FAQ

What is Kirchhoff’s Current Law (KCL)?

KCL states that the total current entering a junction equals the total current leaving the junction, based on the conservation of electric charge.

How does Kirchhoff’s Voltage Law (KVL) work?

KVL states that the sum of all electrical potential differences around any closed loop in a circuit is zero, reflecting the conservation of energy.

When should I use KCL and KVL?

Use KCL when analyzing currents at junctions and KVL when analyzing voltage around loops in a circuit.

Can Kirchhoff’s Laws be applied to AC circuits?

Yes, Kirchhoff’s Laws can be extended to AC circuits by incorporating complex impedances and using phasor representations.

What are common mistakes when applying Kirchhoff’s Laws?

Common mistakes include misassigning voltage polarities, overlooking elements in loops or junctions, and confusing KCL with KVL.

How can I efficiently solve circuits using Kirchhoff’s Laws?

Identify all junctions and loops, systematically apply KCL and KVL to set up equations, and use techniques like mesh analysis or node-voltage method to solve them efficiently.

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

Get PDF

PDF

Explore

Your Flashcards are Ready!

Use Kirchhoff’s Laws to Solve Simple Circuit Problems

Introduction

Key Concepts

Understanding Kirchhoff’s Laws

Kirchhoff’s Current Law (KCL)

Kirchhoff’s Voltage Law (KVL)

Applying Kirchhoff’s Laws to Simple Circuits

Example Problem

Superposition Principle in Kirchhoff’s Laws

Node-Voltage Method

Thevenin’s and Norton’s Theorems

Analysis of Parallel and Series Circuits

Advanced Concepts

Mathematical Derivations of Kirchhoff’s Laws

Derivation of Kirchhoff’s Current Law (KCL)

Derivation of Kirchhoff’s Voltage Law (KVL)

Application of Kirchhoff’s Laws in Complex Circuits

Mesh Analysis

Supermesh Concept

Dependent Sources and Kirchhoff’s Laws

Interdisciplinary Connections

Advanced Problem Solving Techniques

Transient Analysis in RC Circuits

Analysis of AC Circuits

Network Theorems Integration

Comparison Table

Summary and Key Takeaways

Coming Soon!

Tips

Did You Know

Common Mistakes

FAQ