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 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter
Overview
Overview
🌳 Concept tree
Lesson 3→Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter
├── Use
├── Construction
├── Action
├── Why the parts are used (typical reasons)
├── Sensitivity
├── The ammeter (shunt)
├── The voltmeter (multiplier)
├── Comparison of ammeter and voltmeter
├── The ohmmeter
- ├── Using the galvanometer to measure current
- emf and resistance
├── Analogue and digital instruments
├── Typical "give reasons" for this chapter
└── Summary of formulas
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 1 / 15
Use
Use
- Detects very weak currents, measures their intensity and determines their direction (polarity).
- It works on the torque on a current-carrying coil in a magnetic field.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 2 / 15
Construction
Construction
- A rectangular coil of many turns of thin insulated copper wire, wound on a light aluminium frame.
- The frame is mounted on a soft-iron cylinder (core) between the poles of a strong permanent horseshoe magnet; the pole pieces are concave (curved) so that the field in the gap is radial.
- The coil is pivoted on jewel (agate) bearings and carries a pointer moving over a scale (zero at the centre in a centre-zero instrument).
- Two spiral (hair) springs, above and below, provide the restoring torque and also act as current leads to the coil.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 3 / 15
Action
Action
- The current in the coil gives a couple τ = BIAN. The coil turns until this torque is balanced by the opposite torque of the twisted springs, which is proportional to the angle of deflection (τspring = c θ, where c is the torsion constant of the springs).
- The radial field and soft-iron core keep the plane of the coil always parallel to the field lines, so the sides always cut the field at 90° and B is the same magnitude at every angle. Then the deflecting torque BIAN is independent of the angle, and the balanced angle θ is proportional to the current → the scale is uniform.
- Reversing the current reverses the deflection.
At balance→B I A N = c θ, so θ = (B A N / c) I. The factor BAN/c is the sensitivity.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 4 / 15
Why the parts are used (typical reasons)
Why the parts are used (typical reasons)
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Soft-iron core |
| concentratesfluxstrengthensfield |
| Spiral springs |
| giverestoringtorqueproportional |
| Light aluminium frame | low inertia and damps the oscillations by eddy currents so the pointer settles quickly | inertiadampsoscillationseddy |
| Concave pole pieces | make the field radial so the scale is uniform | makefieldradialscale |
| Many turns of thin wire and a strong magnet | large torque for a small current (high sensitivity) | largetorquesmallcurrent |
| Permanent magnet (not an electromagnet) | the field must be constant and independent of any current | fieldmustconstantindependent |
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 5 / 15
Sensitivity
Sensitivity
- The sensitivity of a galvanometer is the deflection (in degrees or scale divisions) produced per unit current through the coil, e.g.
- degree/μA.
- It increases with a large number of turns, a larger coil area and a stronger field, and with a weaker control spring (smaller c).
- Example 7a. A galvanometer deflects by 40° when the current is 20 μA. Sensitivity = 40/20 = 2 degree/μA. Because the deflection is proportional to the current, a current of 35 μA gives 70°, and a deflection of 25° indicates a current of 12.5 μA.
✍️ Worked examples
Example 7b — changing the turns.→If the number of turns of this coil is doubled (all else unchanged), the sensitivity doubles to 4 degree/μA.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 6 / 15
The ammeter (shunt)
The ammeter (shunt)
- An ammeter measures current directly and is connected in series in the circuit.
- A galvanometer coil can carry only a very small current Ig (full-scale deflection, FSD).
- To measure a larger current I the instrument is converted a very small resistance, the shunt Rs, is connected in parallel with the galvanometer coil (resistance Rg).
- Reasoning the main current I divides into Ig through the coil and Is through the shunt, so Is = I − Ig. The shunt and the coil have the same potential difference (they are in parallel):
Ig Rg = (I − Ig) Rs
Rs = Ig Rg / (I − Ig)
- Notes:
- The shunt is small, so the combined resistance of the ammeter Rg Rs/(Rg + Rs) is very small, which does not change the current in the circuit when connected in series. In fact this resistance equals Ig Rg / I.
- Most of the current passes through the shunt; only a fraction Ig/I passes through the coil.
- A larger measuring range needs a smaller shunt. To extend the range n times (I = n Ig): Rs = Rg / (n − 1).
- The scale is recalibrated so that full scale reads I, not Ig.
- The pointer in a DC ammeter deflects in one direction, so the positive terminal of the ammeter must be joined to the side nearer the positive pole of the source.
- Example 7. A galvanometer of resistance 4 Ω gives FSD at 10 mA. To read up to 2 A:
- Rs = 0.010 × 4 / (2 − 0.010) = 0.04/1.99 = 0.0201 Ω.
- Example 7c. A galvanometer has Rg = 60 Ω and FSD current 1.5 mA. To convert it into an ammeter of range 0.3 A:
- Rs = 0.0015 × 60 / (0.3 − 0.0015) = 0.09 / 0.2985 = 0.3015 Ω.
- Total resistance of the ammeter = 60 × 0.3015 / 60.3015 = 0.300 Ω (= Ig Rg / I = 0.09/0.3 ✔).
- Example 7d — range ×10. A galvanometer of 36 Ω is to read ten times its FSD current: Rs = 36 / (10 − 1) = 4 Ω in parallel. Check: when the main current is 10 Ig, 9 Ig goes through 4 Ω giving 36 Ig, and Ig goes through 36 Ω giving 36 Ig ✔.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 7 / 15
The voltmeter (multiplier)
The voltmeter (multiplier)
- A voltmeter measures potential difference and is connected in parallel across the part of the circuit concerned.
- The voltage across a galvanometer coil at FSD is tiny (Vg = Ig Rg), so the bare galvanometer could only measure very small voltages.
- To measure larger voltages a large resistance, the multiplier Rm, is connected in series with the coil.
- At FSD the instrument must carry Ig when the voltage across the whole instrument is V:
- V = Ig Rg + Ig Rm → Rm = V / Ig − Rg (equivalently Rm = (V − Vg)/Ig)
- Notes:
- The total resistance of the voltmeter (Rg + Rm) is very large, so it draws a negligible current and does not change the voltage being measured.
- The positive terminal of the voltmeter is connected to the point of higher potential; if the voltage is reversed, the connections must be reversed.
- The multiplier makes the resistance large, so most of the measured voltage is across the multiplier and only a tiny voltage (Ig Rg) is across the coil.
- Example 8. Galvanometer: Rg = 20 Ω, Ig = 5 mA. To read up to 30 V:
- Rm = 30/0.005 − 20 = 6000 − 20 = 5980 Ω in series.
- Example 8a. Rg = 40 Ω, Ig = 1 mA, desired range 12 V: Rm = 12/0.001 − 40 = 11 960 Ω. Total resistance of the voltmeter = 12 000 Ω. For a 3 V range the multiplier would be 3000 − 40 = 2960 Ω.
Example 8b.→What is the effect of the voltmeter resistance? A voltmeter of 12 000 Ω is connected across a 4000 Ω resistor in a circuit. The combination 4000 × 12 000 / 16 000 = 3000 Ω, so the voltmeter lowers the resistance between the two points by 25%, which is why a voltmeter’s resistance must be as large as possible compared with the resistance across which it is placed.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 8 / 15
Comparison of ammeter and voltmeter
Comparison of ammeter and voltmeter
| Comparison aspect | Ammeter | Voltmeter |
|---|---|---|
| Measures | current | potential difference |
| Connected | in series | in parallel |
| Added resistor | small shunt in parallel with the coil | large multiplier in series with the coil |
| Total resistance | very small | very large |
| Effect on circuit if ideal | none (does not change the current) | none (draws no current) |
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 9 / 15
The ohmmeter
The ohmmeter
- An ohmmeter measures an unknown resistance directly.
- Measuring a resistance by Ohm’s law needs both an ammeter and a voltmeter (R = V / I).
- If the voltage is fixed and known, we can drop the voltmeter and mark the galvanometer scale in ohms instead of amperes.
- It is a micro-ammeter (galvanometer) in series with a fixed resistance, a variable resistance (adjusted for zero) and a cell of constant emf (about 1.5 V), with two terminals between which the unknown resistance Rx is connected.
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Zero adjustment | with the terminals touching (Rx = 0, short circuit), the variable resistor is adjusted so that the pointer gives full-scale deflection: Rtotal = VB / Ig. | terminalstouchingshortcircuit |
| • | With Rx inserted the current is I = VB/(Rtotal + Rx), which is smaller, so the deflection is smaller and the scale is calibrated directly in ohms. | insertedcurrentRtotalsmaller |
| Features of the scale |
| zeroohmsfullright |
| • | If Rx = Rtotal the current is half of FSD; if Rx = 2 Rtotal it is one-third FSD, etc. In general, I / Ig = Rtotal / (Rtotal + Rx). | Rtotalcurrenthalfthird |
| Reasons |
| cellmustconstantotherwise |
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Example 9. | An ohmmeter has a 1.5 V cell and a total internal resistance of 3000 Ω at FSD (500 μA). With an unknown resistor of 3000 Ω: I = 1.5/6000 = 250 μA = half of FSD. With 9000 Ω: I = 1.5/12000 = 125 μA = quarter of FSD | ohmmetercelltotalinternal |
| Example 9a — a calibration table. | An ohmmeter has a 1.5 V cell and FSD current 1 mA, so its total internal resistance is 1.5/0.001 = 1500 Ω. For different Rx: | ohmmetercellcurrenttotal |
| Rx | total resistance | current | fraction of FSD |
|---|---|---|---|
| 0 | 1500 Ω | 1.0 mA | 1 |
| 500 Ω | 2000 Ω | 0.75 mA | 3/4 |
| 1500 Ω | 3000 Ω | 0.5 mA | 1/2 |
| 4500 Ω | 6000 Ω | 0.25 mA | 1/4 |
| 13 500 Ω | 15 000 Ω | 0.1 mA | 1/10 |
|
Example 9b — design.→A milliammeter of resistance 20 Ω has FSD 10 mA. It is used as an ohmmeter with a 1.5 V cell of internal resistance 1 Ω. For FSD the total resistance must be 1.5/0.010 = 150 Ω, so the standard resistor needed (including the variable one) is 150 − 20 − 1 = 129 Ω. A reading of 6 mA means the total resistance is 1.5/0.006 = 250 Ω, so Rx = 250 − 150 = 100 Ω. With Rx = 600 Ω the current is 1.5/750 = 2 mA.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 10 / 15
Using the galvanometer to measure current, emf and resistance
Using the galvanometer to measure current, emf and resistance
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| Current | convert it into an ammeter by a shunt and connect it in series | convertammetershuntconnect |
| emf (or potential difference) |
| convertvoltmetermultiplierconnect |
| Resistance |
| convertohmmeterammetervoltmeter |
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 11 / 15
Analogue and digital instruments
Analogue and digital instruments
- Analogue (pointer) meters use a pointer on a scale; a multimeter can be switched to measure current, voltage and resistance.
- Digital multimeters show the value as numerals on an LCD (liquid-crystal display) without a pointer.
- An ohmmeter, which measures resistance, has a non-linear graduated scale.
- Full deflection of the pointer corresponds to zero resistance (a short circuit), and the pointer moves back as the resistance increases.
- For example, the same instrument reads 200 µA when the measured resistance is 3750 Ω, and 100 µA when it is 11250 Ω.
- Because the readings are not evenly spaced, the marks on the right side of the scale are further apart than the marks on the left.
- Digital multimeters do not use a pointer.
- They show the value as numerals on a small liquid-crystal display (LCD), which makes the reading easier to take.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 12 / 15
Typical "give reasons" for this chapter
Typical "give reasons" for this chapter
- A soft-iron cylinder is fixed inside the coil of the galvanometer: to strengthen the field and make it radial.
- The coil is attached to a pair of spiral springs to supply a restoring torque proportional to the angle and to lead the current to the coil.
- A high resistance is connected in series with the galvanometer when it is used as a voltmeter: to limit the current to Ig at FSD and to make the voltmeter draw negligible current.
- An ammeter is connected in series and a voltmeter in parallel: so that the ammeter carries the whole current of the branch and the voltmeter sees the same voltage as the element.
- A constant resistor is placed inside the ohmmeter to protect the meter and fix the calibration.
- The cell of an ohmmeter must have a constant emf a changing emf would make the calibration wrong.
- The scale of the ohmmeter is not linear and runs in the opposite sense to that of the ammeter: because I = VB/(Rtotal + Rx) is not proportional to Rx, and larger resistance gives smaller current.
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 13 / 15
Summary of formulas
Summary of formulas
| Quantity | Formula |
|---|---|
| Flux density | B = Φ/A (tesla = Wb/m2 = N/A·m) |
| Straight wire | B = μI/(2πd) |
| Circular coil (centre) | B = μNI/(2r) |
| Solenoid (axis) | B = μNI/L = μnI |
| Force on a wire | F = BIL sin θ |
| Force between parallel wires | F = μ I₁ I₂ L / (2π d) |
| Torque on coil | τ = BIAN sin θ (θ from field to normal) |
| Magnetic moment | m = NIA |
| Ammeter shunt | Rs = Ig Rg / (I − Ig) |
| Voltmeter multiplier | Rm = V/Ig − Rg |
| Ohmmeter at FSD | Rtotal = VB / Ig |
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Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 14 / 15
Part 15
Part 15
- 📖
🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
Physics Thanaweya Amma (2026/2027)
- Lesson 3 – Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter
- The Moving Coil Galvanometer detects weak DC currents based on magnetic torque.
- By connecting appropriate precision resistors, it converts into a DC Ammeter (using a small parallel shunt resistor Rs), a DC Voltmeter (using a large series multiplier Rm), or an Ohmmeter.
🌳 Hierarchy Classification & Concept Tree
Analog Electromagnetic Instruments
├── 1. Moving Coil Galvanometer (MCG)
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| │ ├── Components |
| Concavemagneticpolescylindrical |
| │ ├── Equilibrium condition | Deflecting magnetic torque = Restoring torsion torque (τ_mag = τ_torsion) | DeflectingmagnetictorqueRestoring |
| │ └── Sensitivity |
| Constantradialfielduniform |
| • | ├── 2. Direct Current Ammeter (Measures large currents) | DirectCurrentAmmeterMeasures |
| │ ├── Conversion | Small resistor (Shunt Rs) connected in PARALLEL with galvanometer | SmallresistorShuntconnected |
| │ └── Shunt formula | Rs = (Ig · Rg) / (I – Ig) | |
| • | ├── 3. Direct Current Voltmeter (Measures high potential differences) | DirectCurrentVoltmeterMeasures |
| │ ├── Conversion | Large resistor (Multiplier Rm) connected in SERIES with galvanometer | LargeresistorMultiplierconnected |
| │ └── Multiplier formula | Rm = (V – Vg) / Ig = (V – Ig · Rg) / Ig | |
| • | └── 4. The Ohmmeter (Measures unknown resistance Rx) | OhmmeterMeasuresunknownresistance |
| ├── Components |
| Galvanometerstandardresistorvariable |
| ├── Total internal resistance | Rinternal = Rg + Rc + Rv + r = VB / Ig | Rinternal |
| └── Scale non-uniformity | I is inversely proportional to total resistance (Rinternal + Rx) | inverselyproportionaltotalresistance |
📋 Master Teacher's Blackboard & Exam Secrets
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| RULE 1 |
| Concavepolescylindricaliron |
| RULE 2 |
| OhmmeterscaleUNIFORMcalibrated |
| RULE 3 |
| currentdropsfullscale |
| RULE 4 |
| Smallershuntresistancedecreases |
| 📊 Comparative Analysis | Instrument Conversion Architecture Comparison | InstrumentConversionArchitectureComparison |
| Instrument | Modifying Resistor | Connection Mode | Primary Function | Ideal Meter Resistance |
|---|---|---|---|---|
| DC Ammeter | Shunt Resistor (Rs: Very small) | Parallel with Galvanometer | Increases current measuring range | Zero (Rammeter → 0) |
| DC Voltmeter | Multiplier (Rm: Very large) | Series with Galvanometer | Increases voltage measuring range | Infinite (Rvoltmeter → ∞) |
| Ohmmeter | Internal calibrated resistors | Series with internal battery | Measures unknown resistor Rx directly | Calibrated internally |
Lesson 3: Analog Measuring Instruments – Galvanometer, Ammeter, Voltmeter and Ohmmeter · 15 / 15
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