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)
More lessons
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: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire
Overview
Overview
🌳 Concept tree
Lesson 1→Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire
├── Faraday's experiment
├── Faraday's law
├── Lenz's rule
- ├── Fleming's right-hand rule (induced current in a moving straight wire)
- └── Induced emf in a straight wire moving in a magnetic field
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 1 / 7
Faraday’s experiment
Faraday’s experiment
- Faraday made a cylindrical coil of insulated copper wire (the turns separated from each other so that they do not short-circuit) and joined its ends to a sensitive galvanometer with its zero at the middle of the scale, so that the pointer can swing either way.
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Plunging a bar magnet into the coil | the pointer deflects momentarily in one direction | pointerdeflectsmomentarilydirection |
| Pulling the magnet out | the pointer deflects momentarily in the opposite direction | pointerdeflectsmomentarilyopposite |
| Holding the magnet still, inside or outside the coil |
| deflectionwhateverstrength |
| • |
| Movingmagnetfastergives |
| • | Keeping the magnet still and moving the coil gives the same effect: only the relative motion matters | Keepingmagnetstillmoving |
- Conclusion an emf and a current are induced in the coil whenever the magnetic flux linked with it changes with time.
- This phenomenon is electromagnetic induction.
- The induced current exists only while the flux is changing.
- Faraday explained it by saying that the induced emf and current appear because the magnetic field lines are cut by the turns of the coil as the magnet moves.
- Also, the coil reacts against the motion of the magnet when the magnet is pushed in, the induced field opposes it (repels it); when pulled out, the induced field tries to keep it in (attracts it).
- You can feel this resistance if the coil has many turns and is short-circuited: it is harder to push the magnet in quickly.
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 2 / 7
Faraday’s law
Faraday’s law
- From his observations Faraday concluded that:
- A relative motion between a conductor and a magnetic field that changes the magnetic flux linked with the conductor induces an emf in it. Its direction depends on the direction of the relative motion.
- The magnitude of the induced emf is proportional to the rate of change of the magnetic flux (the rate at which the conductor cuts the flux lines): emf ∝ ΔΦm / Δt.
- It is also proportional to the number of turns N of the coil that link the flux (each turn contributes the same emf, and they are in series): emf ∝ N.
- Combining these:
emf = − N ΔΦm / Δt
- Φm = B A cos(angle) is the magnetic flux (weber, Wb = T·m2); Δt in seconds.
- The flux is the product of the field and the area that is perpendicular to it, so the flux can change in three ways: B changes, the area A changes, or the angle between the coil and the field changes.
- The factors that increase the induced emf: more turns, a stronger magnet (or field), a faster motion (smaller Δt), an iron core.
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Practical check of Faraday’s law (the usual essay) | connect a coil of N turns to a galvanometer and move a magnet through it | connectcoilturnsgalvanometer |
| (i) Move the magnet slowly, then quickly | the quicker motion (greater rate of change of flux) gives a larger deflection | quickermotiongreaterrate |
| • |
| Repeatcoilsdifferentnumbers |
| (iii) Use a stronger magnet | the deflection increases | deflectionincreases |
| Example 1a. | A coil of 120 turns and area 0.01 m2 has the field through it (perpendicular to the coil) fall from 0.5 T to 0.1 T in 0.04 s. ΔΦ = (0.5 − 0.1) × 0.01 = 4×10−3 Wb. |emf| = 120 × 4×10−3 / 0.04 = 12 V. If the circuit resistance is 24 Ω the induced current is 12 / 24 = 0.5 A | coilturnsareafield |
Example 1b.→A coil of 60 turns and area 0.05 m2 is turned in a 0.4 T field from the position where its plane is perpendicular to the field to the position where it is parallel, in 0.1 s. The flux falls from BA = 0.02 Wb to zero, so |emf| = 60 × 0.02 / 0.1 = 12 V.
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 3 / 7
Lenz’s rule
Lenz’s rule
- The negative sign in Faraday’s law expresses Lenz’s rule:
- The direction of the induced current (and induced emf) is such that its magnetic effect opposes the change in flux that produces it.
- Applications (this is the use of Fig 3-2 in the book):
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| North pole of a magnet approaching a coil | the end of the coil facing the magnet becomes a north pole (repels the magnet). The induced current is anticlockwise as seen from the magnet side. The repulsion resists the motion of the magnet towards the coil | facingbecomesrepelsinduced |
| North pole moving away | the near end becomes a south pole (attracts the magnet and tries to keep it). The attraction resists the motion of the magnet away from the coil | nearbecomessouthattracts |
| Lenz’s rule is a statement of conservation of energy |
| workdoneagainstopposing |
| How to use it |
| decidewhetherfluxthrough |
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 4 / 7
Fleming’s right-hand rule (induced current in a moving straight wire)
Fleming’s right-hand rule (induced current in a moving straight wire)
- Stretch the thumb, forefinger and middle finger of the right hand at right angles to each other.
- If the thumb points in the direction of motion of the wire and the forefinger in the direction of the field (N → S), the middle finger gives the direction of the induced current (emf).
- Compare left hand → motor (current + field → force); right hand → generator (motion + field → current). A useful memory trick: "left for motor, right for generator" — the word "generator" has the letter "r" for right.
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 5 / 7
Induced emf in a straight wire moving in a magnetic field
Induced emf in a straight wire moving in a magnetic field
- A straight wire of length L is perpendicular to a uniform field B and moves with velocity v perpendicular to both the field and the wire.
- In a time Δt it moves a distance Δx = v Δt and sweeps an area ΔA = L Δx = L v Δt, so the flux it cuts is ΔΦ = B ΔA = B L v Δt.
By Faraday’s law (one turn),
emf = B L v
- The negative sign (Lenz’s rule) only tells the direction.
- If the velocity makes an angle θ with the field (wire still perpendicular to the velocity), only the component v sin θ perpendicular to the field cuts the flux lines:
emf = B L v sin θ
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| • |
| maximumwiremovesperpendicular |
| • |
| wirepartclosedcircuit |
| Example 1. | A 0.6 m metal rod moves at 3 m/s perpendicular to a 0.25 T field. emf = 0.25 × 0.6 × 3 = 0.45 V | metalmovesperpendicularfield |
| Example 2. | A coil of 50 turns has its flux changed from 0.04 Wb to 0.01 Wb in 0.1 s. |emf| = 50 × 0.03 / 0.1 = 15 V | coilturnsfluxchanged |
| Example 2a. | A rod of length 45 cm moves at 2 m/s in a direction making 30° with a field of 0.5 T. emf = 0.5 × 0.45 × 2 × sin 30° = 0.225 V | lengthmovesdirectionmaking |
| Example 2b. |
| aircraftwingspanflieshorizontally |
| Example 2c — finding the speed. | A 25 cm rod in a 0.4 T field has an emf of 0.15 V between its ends when moved perpendicular to the field. v = emf / (B L) = 0.15 / (0.4 × 0.25) = 1.5 m/s | fieldbetweenendsmoved |
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 6 / 7
Part 7
Part 7
- 📖
🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
Physics (Thanaweya Amma 2026/2027)
- Lesson 1 – Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire
- Electromagnetic induction is the generation of an induced electromotive force (EMF) and induced electric current in a closed circuit when exposed to a varying magnetic flux.
- Faraday's Law states emf = -N (ΔΦm / Δt), where the negative sign embodies Lenz's Law of opposition.
🌳 Conceptual Hierarchy Tree
Electromagnetic Induction Fundamentals
├── 1. Faraday's Induction Experiment
- │ ├── Moving magnet relative to solenoid coil induces transient galvanometer deflection
- │ └── Faraday's Law emf = -N · (ΔΦm / Δt) = -N · A · (ΔB / Δt)
├── 2. Lenz's Law (Direction of Induced Current)
- │ ├── Principle Induced current always flows in a direction opposing the magnetic flux change producing it
- │ ├── Approaching North Pole → Face becomes North Pole (Repulsion)
- │ └── Receding North Pole → Face becomes South Pole (Attraction)
- └── 3. Induced EMF in a Straight Conductor (Length L, Velocity v)
├── emf = -B · L · v · sin θ
- ├── Direction determined by Fleming's Right-Hand Rule
- └── Maximum when wire moves perpendicular to field; Zero when parallel
📋 Master Teacher's Blackboard Secrets
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| RULE 1 | Lenz's Law embodies the Law of Conservation of Energy: External mechanical work done to overcome repulsive/attractive forces converts into electrical energy | LenzembodiesConservationEnergy |
| RULE 2 |
| FlemingRIGHTHandINDUCED |
| RULE 3 | If a loop is rotated in a magnetic field: ΔΦm = 2 B A when rotated 180° (reversed) from perpendicular position | looprotatedmagneticfield |
| EXAM TRAP |
| induceddependsRATEchange |
| 📊 Matrix | Comparative Analysis: Lenz's Law Magnetic Opposition Responses | ComparativeAnalysisLenzMagnetic |
| Magnet Relative Motion | Flux Change (ΔΦm) | Induced Coil Pole Formed | Direction of Induced Current |
|---|---|---|---|
| North Pole Approaching | Increasing (+ΔΦm) | North Pole (Repulsive force) | Counter-Clockwise |
| North Pole Receding | Decreasing (-ΔΦm) | South Pole (Attractive force) | Clockwise |
| South Pole Approaching | Increasing (+ΔΦm) | South Pole (Repulsive force) | Clockwise |
| South Pole Receding | Decreasing (-ΔΦm) | North Pole (Attractive force) | Counter-Clockwise |
| Magnet Stationary Inside Coil | Zero change (ΔΦm = 0) | No pole formed | Zero induced current (I = 0) |
Lesson 1: Faradays Law of Induction, Lenzs Law and EMF in a Moving Wire · 7 / 7
Well done! You finished this lesson
What would you like to do next?