Alternating Current (AC) and Electronics

Grade 12 · Physics

Semester 2 | Period 4 | Week 21

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Subject: Physics

Semester: 2

Period: 4

Week: 21

School Name:

Teacher’s Name:

Subject: Physics

Grade Level: Grade 12

Week & Period: Week 21, Period IV

Date:

Main Topic: Alternating Current (AC) and Electronics
Sub-Topic: Resonance in RLC Circuits

Learning Objectives:

By the end of this lesson, learners should be able to:

  1. Define electrical resonance in an RLC series circuit.
  2. Derive and apply the formula for resonant frequency.
  3. Explain the conditions necessary for resonance.
  4. Analyze current behavior in resonance.
  5. Conduct and interpret a resonance experiment using function generators.

 

Instructional Materials:

  • Function generator or variable-frequency AC source
  • Resistor (R), Inductor (L), Capacitor (C)
  • Voltmeter and Ammeter
  • Oscilloscope (optional)
  • Multimeter
  • Wires and breadboard

 

Anticipatory Set (Warm-Up):

Pose this real-life scenario:

“Tuning a radio involves adjusting a knob to receive the clearest sound. What do you think is happening electrically inside the radio?”
Use this to introduce the idea of resonance — maximum response at a particular frequency.

 

Building Knowledge (Main Lesson):

  1. Definition of Resonance:
  • In an RLC series circuit, resonance occurs when the inductive reactance equals the capacitive reactance:

     

Experiment: Investigating Resonance in an RLC Circuit

Objective: To determine the resonant frequency in an RLC circuit.

Materials Needed:

  • Function generator (10–100 Hz range)
  • 100Ω resistor
  • 0.05 H inductor
  • 200 μF capacitor
  • AC ammeter
  • Voltmeter
  • Connecting wires
  • Breadboard

Procedure:

  1. Connect R, L, and C in series across a function generator.
  2. Set the frequency to 10 Hz and gradually increase it.
  3. Record the current at each frequency.
  4. Note the frequency at which the current is maximum — that is the resonant frequency.

Observation: The current increases to a peak at resonance and then decreases again.

Conclusion: At resonance, the impedance is minimum and the power transfer is maximum.

 

Activities and Guided Practice:

  • Derive the resonance formula in small groups.
  • Predict resonant frequency given different values of L and C.
  • Use graph paper to plot current vs frequency — identify the resonance point.

 

Assessment:

Classwork:

  1. What is resonance in an RLC circuit?
  2. If L=0.1H and C=100 μF, calculate the resonant frequency.
  3. Sketch a graph of current vs frequency in a resonant RLC circuit.

Homework:

  1. A circuit resonates at 60 Hz. What happens if the frequency is changed to 80 Hz?
  2. Explain one application of electrical resonance in real life.
  3. Describe the energy transfer in an RLC circuit at resonance.

 

Differentiation:

  • Use animations to show the variation of impedance with frequency.
  • Let practical learners vary components and directly observe changes.
  • Use analogies (e.g., child on a swing = resonance).

 

Teacher’s Reflection:

  • Were learners able to observe resonance in real time?
  • Did they connect theory with experimental results?
  • What support do struggling learners need for calculations?