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Lesson Notes

වියාචනය (Disclaimer)

Idasara Academy ඉගෙනුම් සම්පත් නිර්මාණය කර ඇත්තේ සිසුන්ට මගපෙන්වීම, පුහුණුව සහ අධ්‍යයන උපායමාර්ග ලබාදී සහයෝගය දැක්වීමටය.

කෙසේ වෙතත්, සියලුම විභාග සහ නිල අවශ්‍යතා සඳහා, සිසුන් අනිවාර්යයෙන්ම ශ්‍රී ලංකා අධ්‍යාපන අමාත්‍යාංශයේ, අධ්‍යාපන ප්‍රකාශන දෙපාර්තමේන්තුව විසින් ප්‍රකාශයට පත් කරන ලද නිල පෙළපොත් සහ සම්පත් පරිශීලනය කළ යුතුය.

ජාතික විභාග සඳහා අන්තර්ගතයේ නිල බලය ලත් මූලාශ්‍රය වනුයේ රජය විසින් නිකුත් කරනු ලබන මෙම ප්‍රකාශනයි.

Unit 8: Electromagnetism

Grade

13

Lesson 8.1 – Magnetic Fields & Magnetic Force 


Foundation (Q1–5)

  1. Define a magnetic field.

  2. What is meant by magnetic flux density (B)?

  3. State Fleming’s Left-Hand Rule.

  4. Write the formula F = BIL.

  5. What is a uniform magnetic field?


Intermediate (Q6–10)

  1. A 2 m wire carries 3 A in a 0.4 T field. Find force.

  2. Explain why a current-carrying conductor experiences a force.

  3. Distinguish between magnetic field and magnetic force.

  4. Draw magnetic field around a straight current-carrying wire.

  5. Resolve force direction using Fleming’s rule.


Advanced (Q11–15)

  1. Derive F = BIL sinθ.

  2. Analyse force on moving charge F = qvB.

  3. Explain why force is zero when motion is parallel to field.

  4. Calculate charge velocity given force, B, and q.

  5. Compare magnetic force on electrons and protons.



Lesson 8.2 – Magnetic Fields of Conductors & Solenoids 


Foundation (Q1–5)

  1. State Biot–Savart law qualitatively.

  2. Draw field around straight wire.

  3. State formula B = μ₀I/2πr.

  4. Define solenoid.

  5. Write B = μ₀nI.


Intermediate (Q6–10)

  1. Calculate B at 4 cm from wire carrying 5 A.

  2. Explain why solenoid field is uniform.

  3. Use right-hand grip rule for direction of field.

  4. Compare inside vs outside field in solenoid.

  5. Show effect of increasing number of turns.


Advanced (Q11–15)

  1. Derive B = μ₀nI.

  2. Analyse toroid field distribution.

  3. Calculate field at point due to multiple wires.

  4. Discuss effect of core material in solenoid.

  5. Explain ideal vs non-ideal solenoid.



Lesson 8.3 – Electromagnetic Induction (Faraday & Lenz) 


Foundation (Q1–5)

  1. Define electromagnetic induction.

  2. State Faraday’s law.

  3. Write emf formula ε = −dΦ/dt.

  4. What does negative sign indicate?

  5. Define magnetic flux (Φ).


Intermediate (Q6–10)

  1. A coil experiences flux change of 0.2 Wb in 0.1 s. Calculate emf.

  2. Explain Lenz’s law using energy conservation.

  3. Draw induced current direction for moving magnet–coil system.

  4. Discuss factors affecting induced emf.

  5. Distinguish between mutual and self-induction.


Advanced (Q11–15)

  1. Derive Faraday’s law mathematically.

  2. Analyse induced emf in rotating coil.

  3. Explain back emf in motors.

  4. Calculate induced emf in rod moving in magnetic field.

  5. Discuss eddy currents and ways to reduce them.



Lesson 8.4 – Alternating Current (AC) & RMS 


Foundation (Q1–5)

  1. Define alternating current.

  2. Write V = V₀ sinωt.

  3. What is RMS value?

  4. Write Irms = I₀/√2.

  5. Sketch AC waveform.


Intermediate (Q6–10)

  1. Calculate RMS voltage for V₀ = 100 V.

  2. Explain frequency and angular frequency.

  3. Distinguish AC and DC.

  4. Draw voltage–time graph for AC.

  5. Explain power factor.


Advanced (Q11–15)

  1. Derive RMS value mathematically.

  2. Analyse phase difference between voltage and current.

  3. Solve AC power problem P = Vrms Irms cosφ.

  4. Compare AC transmission advantages.

  5. Explain phasor diagrams.



Lesson 8.5 – Inductive & Capacitive Reactance 


Foundation (Q1–5)

  1. Define reactance.

  2. Write XL = ωL.

  3. Write XC = 1/ωC.

  4. What is impedance (Z)?

  5. Define resonance.


Intermediate (Q6–10)

  1. Calculate inductive reactance for L = 0.2 H at 50 Hz.

  2. A 20 μF capacitor at 60 Hz. Find XC.

  3. Explain how inductors oppose changes in current.

  4. Explain how capacitors oppose changes in voltage.

  5. Draw impedance triangle.


Advanced (Q11–15)

  1. Derive formula for impedance Z = √(R² + (XL − XC)²).

  2. Analyse RLC resonance condition.

  3. Solve RLC current magnitude problem.

  4. Explain bandwidth and quality factor.

  5. Compare inductive & capacitive circuits using phasors.



Lesson 8.6 – Transformers 


Foundation (Q1–5)

  1. Define transformer.

  2. What is step-up transformer?

  3. State Vs/Vp = Ns/Np.

  4. What is ideal transformer?

  5. State two energy losses in transformers.


Intermediate (Q6–10)

  1. Calculate Vs for Ns/Np = 4 and Vp = 50 V.

  2. Explain role of soft iron core.

  3. Describe eddy current losses.

  4. Distinguish step-up vs step-down.

  5. Explain transformer efficiency.


Advanced (Q11–15)

  1. Derive transformer equation using Faraday’s law.

  2. Solve power conservation problem.

  3. Analyse effect of leakage flux.

  4. Discuss role of laminated cores.

  5. Investigate voltage regulation under load.



Lesson 8.7 – Generators & Motors 


Foundation (Q1–5)

  1. Define generator.

  2. Define motor.

  3. State Fleming’s Right-Hand Rule.

  4. What is commutator?

  5. Distinguish AC & DC generator.


Intermediate (Q6–10)

  1. Explain working principle of AC generator.

  2. Explain how DC motor works.

  3. Draw generator emf vs time graph.

  4. Discuss function of brushes.

  5. Explain back emf in DC motor.


Advanced (Q11–15)

  1. Derive emf for rotating coil ε = NBLω sinωt.

  2. Analyse motor torque expression.

  3. Compare efficiency factors of motors.

  4. Explain how generators and motors are reversible machines.

  5. Solve induced emf problem for given rotational speed.


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