Curriculum
Physics
Chapter 1 - Electric Current, Ohms Law and Kirchhoffs Laws
0/20
Chapter 2 - Magnetic Effects of Electric Current and Measuring Instruments
0/223.1Use3.2Construction3.3Action3.4Why the parts are used (typical reasons)3.5Sensitivity3.6The ammeter (shunt)3.7The voltmeter (multiplier)3.8Comparison of ammeter and voltmeter3.9The ohmmeter3.10Using the galvanometer to measure current, emf and resistance3.11Analogue and digital instruments3.12Typical "give reasons" for this chapter3.13Summary of formulas
Chapter 3 - Electromagnetic Induction and AC Dynamo and Transformer
0/24Chapter 4 - Alternating Current AC Circuits
0/301.1Alternating current1.2Advantages of AC1.3The hot-wire ammeter1.4Non-inductive ohmic resistor1.5Pure inductor (coil of zero ohmic resistance)1.6Inductive reactance1.7Capacitor and DC1.8Capacitor and AC1.9Capacitive reactance1.10Combinations of capacitors1.11Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula1.12📌 Comprehensive Scientific Terminology Dictionary:1.13🔍 In-Depth Explanations, Deductions & Multi-Book Insights:1.14Lesson summary
2.1Impedance2.2Phase relationships in a series circuit2.3R–L series circuit2.4R–C series circuit2.5R–L–C series circuit2.6Power2.7Variation with frequency2.8Worked examples (new values)2.9The oscillating (LC) circuit2.10Resonance2.11Tuning a radio receiver2.12Summary of formulas2.13Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula2.14📌 Comprehensive Scientific Terminology Dictionary:2.15🔍 In-Depth Explanations, Deductions & Multi-Book Insights:2.16Lesson summary
Chapter 5 - Dual Nature of Wave and Particle
0/331.1Before we start: why "modern" physics?1.2What we already know about light1.3Hot bodies radiate1.4Features of the Planck curve1.5Applications of thermal radiation1.6The black body1.7The failure of classical physics (the "ultraviolet catastrophe")1.8Planck's explanation (1900)1.9Worked examples (Lesson 1)1.10Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula1.11Lesson 1 - Blackbody Radiation, Planck Hypothesis and Photoelectric Effect1.12Lesson summary
2.1Why electrons stay inside a metal2.2Thermionic emission and the cathode-ray tube (CRT)2.3The photoelectric effect2.4Einstein's explanation (1905)2.5Stopping potential and the graphs2.6Using the energy unit eV2.7Worked examples (Lesson 2)2.8The Compton effect2.9Properties of the photon2.10Radiation force (light pressure)2.11Macroscopic and microscopic models of light2.12Reflection or transmission of photons2.13Worked examples (Lesson 3)2.14De Broglie's idea (1923)2.15Why do we not notice the wave nature of a ball?2.16Wavelength of an accelerated electron2.17The electron microscope2.18Comparison: optical and electron microscope2.19Worked examples (Lesson 4)2.20Chapter summary (key points)2.21Common mistakes to avoid
Chapter 6 - Atomic Spectra and X-Rays
0/281.1Why a new model was needed1.2Bohr's postulates (hydrogen atom)1.3Radii and energies of the hydrogen atom1.4Excitation and emission in hydrogen1.5The series of the hydrogen spectrum1.6Limitations1.7Worked examples (Lesson 1)1.8The spectrometer1.9Types of spectra1.10Worked examples (Lesson 2)1.11What are X-rays?1.12Properties of X-rays1.13Production: the Coolidge tube1.14The X-ray spectrum1.15Origin of the characteristic radiation1.16Origin of the continuous radiation (bremsstrahlung)1.17Comparison of characteristic and continuous X-rays1.18Applications of X-rays1.19Worked examples (Lesson 3)1.20Going deeper — how Bohr's numbers are obtained, and a problem-solving workshop1.21Derivation of the radius and energy (hydrogen)1.22Understanding the energy-level diagram1.23Ionisation, excitation and de-excitation1.24More worked examples1.25X-ray quantities for practice1.26Exam-style reasoning guide1.27Chapter summary1.28Common mistakes
Chapter 7 - Lasers and Principles
0/311.1Energy levels and transitions1.2Comparison between spontaneous and stimulated emission1.3Worked examples (Lesson 1)1.4Properties of the laser beam1.5Monochromaticity (spectral purity)1.6Collimation (a parallel narrow beam)1.7Coherence1.8Intensity (concentration)1.9Worked examples (Lesson 2)1.10Population inversion1.11The three essential elements of any laser1.12Laser action step by step1.13Worked examples (Lesson 3)1.14Construction1.15Operation1.16Applications of lasers1.17Holography (3-D photography)1.18Medicine1.19Other applications1.20Why a threshold? (gain versus loss)1.21Continuous and pulsed operation1.22A guide to common lasers1.23Eye safety and classes1.24Photon arithmetic for laser problems1.25Typical exam questions and model answers (outline)1.26Chapter summary1.27Common mistakes1.28Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula1.29📌 Comprehensive Scientific Terminology Dictionary:1.30🔍 In-Depth Explanations, Deductions & Multi-Book Insights:1.31Lesson summary
Chapter 8 - Modern Electronics and Semiconductors
0/311.1Conductors, insulators and semiconductors1.2The silicon crystal1.3Free electrons and holes1.4Motion of holes1.5Conduction in a semiconductor compared with a metal1.6Sensitivity of semiconductors1.7Worked examples (Lesson 1)1.8Why dope?1.9n-type semiconductor (donor impurities)1.10p-type semiconductor (acceptor impurities)1.11The law of mass action1.12Summary comparison1.13Worked examples (Lesson 2)1.14Formation of the junction1.15Biasing the junction1.16The diode as a switch and as a rectifier1.17Electronic tuning (the varactor)1.18Worked examples (Lesson 3)1.19Structure1.20Operation (n-p-n, common base)1.21Current ratios1.22The transistor as an amplifier1.23The transistor as a switch (and inverter)1.24Worked examples (Lesson 4)
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0/831.1Key terms1.2Laws and key relationships1.3Boyle's Law and Isothermal Compression Mechanics1.4Charles's Law, Absolute Zero, and the Kelvin Temperature Scale1.5The General Gas Law and Ideal Gas Mixtures1.6Comparison1.7Worked examples1.8Exam tips1.9Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula1.10🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
2.1Key terms2.2Laws and key relationships2.3Intensive Physics of Density and Non-Contracting Fluid Mixtures2.4Liquid Pressure at Depth and Manometric Measuring Instruments2.5Pascal's Principle and Hydraulic Systems2.6Worked examples2.7Exam tips2.8Real-world applications2.9Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula2.10📌 Comprehensive Scientific Terminology Dictionary:2.11🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
4.1Key terms4.2Laws and key relationships4.3Torricellian Barometer and Standard Atmospheric Pressure4.4The U-Tube Manometer and Immiscible Fluids Hydrostatic Equilibrium4.5Pascal's Principle and Hydraulic Engineering Systems4.6Comparison4.7Worked examples4.8Exam tips4.9Key Scientific Tables & Anatomical Diagrams Extracted from Official Curricula4.10🔍 In-Depth Explanations, Deductions & Multi-Book Insights:4.11Lesson summary
Text lesson
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity
Overview
Overview
🌳 Concept tree
- Lesson 1 Electric Current, Potential Difference, Resistance and Resistivity
- ├── Electric current
- ├── Potential difference
- ├── Electromotive force (emf) of a source
- ├── Resistance and resistivity
- ├── Ohm's law
- └── Direction of current
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 1 / 8
Electric current
Electric current
- Electric current is the ordered flow of electric charges through a conducting material.
- In a metal the charge carriers are free electrons; in an electrolyte they are positive and negative ions; in a gas they can be both ions and electrons.
- Without a potential difference the free electrons of a metal move randomly in all directions, so there is no net flow of charge across any section of the wire.
- When a source is connected, an electric field is set up along the conductor and the electrons acquire a small, steady drift in the direction opposite to the field, superimposed on their random motion.
- This ordered drift is the current.
Current intensity (I) is the quantity of charge that crosses a section of the conductor each second:
I = Q / t
Q is the charge in coulomb (C), t is the time in second (s) and I is in ampere (A). So 1 A = 1 C/s: one ampere is the current when one coulomb of charge passes a section every second.
- Charge passed in a given time Q = I × t. Always convert minutes or hours into seconds first (1 min = 60 s, 1 h = 3600 s). A very common mistake is to leave the time in minutes.
The number of electrons that carry a charge Q is n = Q / e, where e = 1.6 × 10−19 C is the charge of one electron.
The current is measured by an ammeter, which is always connected in series in the branch whose current is wanted (it must have a very small resistance so that it does not change the current it measures).
Worked example 1.1.A current of 4.5 A flows through a lamp for 2 minutes. Find the charge that passes and the number of electrons involved.
Step 1t = 2 × 60 = 120 s.
Step 2Q = I t = 4.5 × 120 = 540 C.
Step 3n = Q / e = 540 / (1.6 × 10−19) = 3.375 × 1021 electrons.
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 2 / 8
Potential difference
Potential difference
The potential difference (voltage) between two points is the work done to move one coulomb of charge between them:
V = W / Q
W is in joule, Q in coulomb, V in volt, so 1 V = 1 J/C. Two points have a potential difference of one volt when one joule of work is needed to carry one coulomb from one point to the other.
- It follows that W = V Q = V I t the energy delivered to a part of a circuit equals the voltage across it times the charge that passes through it.
- Potential difference is measured by a voltmeter, which is always connected in parallel across the two points.
- It must have a very large resistance so that it takes almost no current from the circuit.
Worked example 1.2.→The work done in moving 8 C of charge between two terminals is 120 J. The potential difference is V = W / Q = 120 / 8 = 15 V. If instead a 6 V battery moves 25 C round a circuit, the energy it supplies is W = V Q = 6 × 25 = 150 J.
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 3 / 8
Electromotive force (emf) of a source
Electromotive force (emf) of a source
- The emf of a source (VB) is the total work done to move one coulomb of charge round the whole circuit, both outside the source and inside it. Its unit is also the volt.
- The emf is a property of the source itself (cell, battery, generator): it tells how much energy the source gives to each coulomb. It is different from the potential difference across the terminals, which is smaller than the emf whenever the source delivers current (see Lesson 3).
- A way to picture the idea is to think of the source as a pump in a water circuit. The pump gives energy to the water; the pipes (the resistors) waste that energy as friction. The emf is the energy given per coulomb by the "pump"; the potential differences across the resistors are the energy lost per coulomb in each part of the path.
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 4 / 8
Resistance and resistivity
Resistance and resistivity
Resistance
- (R) is the opposition a conductor offers to the flow of current.
- Unit: ohm (Ω).
- One ohm is the resistance of a conductor in which a current of one ampere flows when a potential difference of one volt is applied across its ends.
At constant temperature the resistance of a uniform wire depends on:
- its length L (R ∝ L): a longer wire means the electrons collide with more atoms on the way,
- its cross-sectional area A (R ∝ 1/A): a thicker wire offers more parallel paths,
- the material it is made of (through the resistivity ρ).
Combining the three factors:
R = ρ L / A
L in metre, A in m2, R in Ω, so ρ is in Ω·m.
- Resistivity (ρ) the resistance of a wire of that material of unit length and unit cross-sectional area (a 1 m cube between opposite faces). It depends only on the type of material and the temperature, not on the shape or size of the sample. It is why we can compare materials: silver, copper and aluminium have very small ρ; nichrome and constantan have large ρ; glass and rubber have enormous ρ.
- Conductivity (σ) is the reciprocal of resistivity σ = 1 / ρ with unit Ω−1·m−1 (siemens per metre). Good conductors have small ρ and large σ; insulators the opposite.
For a round wire A = π r2 = π d2 / 4, so doubling the diameter divides the resistance by 4 (same length and material). Reading the formula the other way: a wire with half the diameter has four times the resistance.
- Resistance is not a property of the material alone (that is ρ).
- Two copper wires of different length and thickness have different resistances but identical resistivities.
If a wire is stretched (or drawn) to a new length, its volume stays constant: L₁A₁ = L₂A₂. So when the length is multiplied by k, the area is divided by k and the resistance is multiplied by k2.
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Worked example 1.3 (resistivity). |
| nichromewirelengthdiameter |
| Step 1 | radius = 0.20 mm = 2.0 × 10−4 m | radius |
| Step 2 | A = π r2 = 3.14 × (2.0 × 10−4)2 = 1.257 × 10−7 m2 | |
| Step 3 | R = ρ L / A = 1.1 × 10−6 × 5 / 1.257 × 10−7 = 43.8 Ω | |
| Worked example 1.4 (ratio problem). |
| Wirelengthdiametermade |
| • |
| Samematerial |
| • |
| Area |
| • | Hence R₂ / R₁ = (L₂ / L₁) × (A₁ / A₂) = 3 × 4 = 12 | Hence |
| • | So R₂ : R₁ = 12 : 1 | |
| Worked example 1.5 (stretching). |
| wireresistancedrawnuniformly |
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 5 / 8
Ohm’s law
Ohm’s law
At constant temperature, the current through a conductor is directly proportional to the potential difference across its ends:
V = I R (R = V / I; on a graph of V against I the slope is R)
- A conductor that obeys this law (straight V–I line through the origin) is called an ohmic conductor.
- Metallic wires at constant temperature are ohmic; a lamp filament, a diode and an electrolyte-with-gas tube are not, because their resistance changes as they heat up or as the voltage changes.
Ohm’s law has three forms, and you should switch freely between them: I = V / R, V = I R and R = V / I.
- Why "at constant temperature"?
- When current flows, the wire heats up, its atoms vibrate more and the collisions of the electrons increase, so the resistance of a metal rises with temperature.
- A graph of V against I for a long-lasting current in a filament therefore bends upward instead of staying straight.
Worked example 1.6.→An electric kettle element has a resistance of 48 Ω and is connected to a 230 V supply. I = V / R = 230 / 48 = 4.79 A. If a student measures 2.0 A through an unknown resistor under 9.0 V, R = 9 / 2 = 4.5 Ω.
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 6 / 8
Direction of current
Direction of current
- By convention (the conventional current) current flows outside the source from the positive terminal to the negative terminal. This is opposite to the actual motion of the free electrons in the metal. Inside the source the conventional current goes from negative to positive, driven by the chemical (or other) energy of the source.
- All circuit diagrams, and all the sign rules you will use later with Kirchhoff’s laws, use the conventional direction.
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Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 7 / 8
Part 8
Part 8
- 📖
🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
Physics Thanaweya Amma (2026/2027)
- Lesson 1 – Electric Current, Potential Difference, Resistance and Resistivity
- Electric current is the continuous flow of free charges through a conducting wire.
- We analyze current intensity (I = Q/t), potential difference (V = W/Q), electric resistance (R = ρ·L/A), and the physical nature of electrical resistivity (ρ) and conductivity (σ).
🌳 Hierarchy Classification & Concept Tree
Fundamental Electrodynamics
- ├── 1. Electric Current Intensity (I = Q/t = n·e/t)
- │ ├── Direction Conventional (Positive to Negative) vs. Actual Electronic (Negative to Positive)
- │ └── Units Ampere (A) = Coulomb/second (C/s)
- ├── 2. Potential Difference & Electromotive Force (V = W/Q)
- │ ├── Work required to transfer unit charge between two points
- │ └── Battery EMF (VB) Total work done by battery inside and outside the source
└── 3. Electric Resistance & Resistivity
├── Factors affecting resistanceLength (L), Area (A), Temperature (T), Material
├── Resistivity (ρ = R·A/L, unitΩ·m) – Dependent ONLY on material and temperature
└── Electrical Conductivity (σ = 1/ρ, unitΩ−1·m−1 or S/m)
📋 Master Teacher's Blackboard & Exam Secrets
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| RULE 1 |
| ResistivityConductivityintrinsicmaterial |
| RULE 2 |
| wirestretcheddrawnvolume |
| RULE 3 | Current through an ohmic conductor at constant temperature is directly proportional to the potential difference across its terminals (Ohm's Law: V = I · R) | Currentthroughohmicconductor |
| 📊 Comparative Analysis | Comparative Analysis: Electrical Parameters and Units | ElectricalParametersUnits |
| Physical Quantity | Symbol & Formula | SI Unit & Equivalents | Dependence on Wire Dimensions |
|---|---|---|---|
| Electric Current | I = Q/t | Ampere (A) = C/s | Independent (set by V and R) |
| Potential Difference | V = W/Q | Volt (V) = J/C | Set by external battery / circuit |
| Resistance | R = ρ·L/A | Ohm (Ω) = V/A | Proportional to L, inversely to A |
| Resistivity | ρ = R·A/L | Ohm·meter (Ω·m) | Completely INDEPENDENT of L and A |
| Conductivity | σ = 1/ρ | Ohm−1·m−1 (S/m) | Completely INDEPENDENT of L and A |
Lesson 1: Electric Current, Potential Difference, Resistance and Resistivity · 8 / 8
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