Lesson Note on Filtration: Filter Circuits and Uses for SS1 (SSS 1)

Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 10
Age: 15 years
Duration: 45 minutes
Subject: Basic Electricity
Curriculum Theme: Basic Electricity
Previous Lesson: Rectification: AC to DC and Rectifier Circuits.
Topic: FILTRATION
Subject Matter: definition of filtration in power circuits, types of filter circuits, uses of filters, practical operation of rectifier and filter circuits

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define filtration in power circuits.
• Identify and describe different types of filter circuits.
• State the uses of filter circuits.

Affective Domain:

• Appreciate the importance of filter circuits in electronic devices.
• Show interest in the practical application of basic electricity principles.

Psychomotor Domain:

• Observe and describe the smoothing effect of a filter circuit on a rectified output.
• Draw simple diagrams of filter circuits.

Social Domain:

• Participate actively in class discussions and observations.

Reference Materials

The following resources were used in planning this lesson:

• 9 Years Basic Education Curriculum for Basic Technology (Senior Secondary).
• State Unified Scheme of Work for Senior Secondary School Basic Electricity.
• Nelkon and Parker, Advanced Level Physics.
• Basic Electricity for Senior Secondary Schools, Book 3.

Instructional Materials

The teacher will teach this lesson with the aid of:

• Capacitors
• Diodes
• Breadboard
• Oscilloscope or multimeter
• Circuit diagrams of rectifier and filter circuits.

Rationale for the Lesson

This lesson helps pupils understand how electronic devices get a smooth, steady power supply from the AC mains. It explains the role of filters in converting pulsating DC from rectifiers into a more stable DC, which is essential for the proper functioning of most electronic gadgets they use daily.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of alternating current (AC) and direct current (DC), basic electronic components like resistors, capacitors, and diodes, and the principles of rectification.

Lesson Content/Board Summary

FILTRATION

Definition of Filtration in Power Circuits

Filtration in power circuits is the process of smoothing out the pulsating direct current (DC) output from a rectifier circuit, converting it into a more stable and constant DC voltage.

This process removes ripples or unwanted AC components present in the rectified DC, making it suitable for powering sensitive electronic devices.

Purpose of Filter Circuits

The main purpose of filter circuits is to reduce the ripple content in the output of a rectifier.

They help to provide a steady DC voltage that is required for the stable operation of electronic devices.

Types of Filter Circuits

The following are common types of filter circuits:

• Capacitor Filter (Shunt Capacitor Filter): This is the simplest and most common type. A large capacitor is connected in parallel (shunt) with the load. It charges during the peaks of the rectified voltage and discharges slowly through the load during the valleys, smoothing the output.
• Inductor Filter (Series Inductor Filter): An inductor is connected in series with the load. Inductors oppose changes in current, thus smoothing out the current variations and reducing ripple.
• LC Filter (L-section or Pi-section): These combine inductors and capacitors to provide better filtering than individual components. An L-section filter uses one inductor and one capacitor, while a Pi-section filter uses two capacitors and one inductor.
• RC Filter: Uses resistors and capacitors in combination to filter out ripples. Less efficient than LC filters but simpler for light loads.

Uses of Filters

Filter circuits are used in various electronic applications. The following are some uses:

• Power supply units for all electronic devices (e.g., mobile phone chargers, televisions, computers).
• Audio amplifiers to remove hum and noise.
• Radio receivers and transmitters to separate desired signals from unwanted frequencies.
• Medical equipment and industrial control systems requiring stable DC power.

Practical Operation of Rectifier and Filter Circuits

A rectifier converts AC to pulsating DC.

A filter circuit (e.g., a capacitor filter) is then connected across the output of the rectifier.

The capacitor charges to the peak voltage of the rectified waveform.

When the rectified voltage drops, the capacitor discharges through the load, maintaining a relatively constant output voltage and reducing the ripple.

The effectiveness of the filter can be observed using an oscilloscope, which shows a much smoother waveform compared to the unfiltered rectified output.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Set Induction

Teacher’s Activity: The teacher greets the pupils and reminds them about the previous lesson on rectification, asking them to recall what a rectifier does and why we need DC for most electronic devices.

Pupils’ Activity: Pupils respond to the questions and recall previous knowledge about rectifiers.

Learning Point: Pupils connect current lesson to previous knowledge.

Step 2: Presentation of Lesson Topic

Time: 3 minutes

Teaching Skill: Explanation

Teacher’s Activity: The teacher introduces the topic “FILTRATION” and writes it on the board, explaining that after rectification, the DC is not perfectly smooth and needs further processing.

Pupils’ Activity: Pupils pay attention and write the topic in their notebooks.

Learning Point: Pupils are aware of the lesson’s focus.

Step 3: Definition and Purpose of Filtration

Time: 7 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher defines filtration in power circuits and explains its purpose, highlighting the need to remove ripples from the rectified DC. The teacher uses simple analogies if needed.

Pupils’ Activity: Pupils listen, ask questions for clarification, and take notes on the definition and purpose.

Learning Point: Pupils understand what filtration is and why it is necessary.

Step 4: Types of Filter Circuits

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains and draws diagrams of different types of filter circuits, focusing on the capacitor filter, and briefly mentioning inductor, LC, and RC filters. The teacher explains how each component contributes to smoothing.

Pupils’ Activity: Pupils observe the diagrams, ask questions, and draw the circuit diagrams in their notebooks.

Learning Point: Pupils can identify and understand the basic operation of different filter types.

Step 5: Uses of Filters

Time: 5 minutes

Teaching Skill: Enumeration/Discussion

Teacher’s Activity: The teacher discusses various practical uses of filter circuits in everyday electronic devices, encouraging pupils to suggest examples.

Pupils’ Activity: Pupils contribute examples and note down the uses of filters.

Learning Point: Pupils appreciate the real-world applications of filter circuits.

Step 6: Practical Demonstration of Rectifier and Filter Circuits

Time: 10 minutes

Teaching Skill: Demonstration/Observation

Teacher’s Activity: Using the breadboard, diodes, capacitor, and oscilloscope/multimeter, the teacher demonstrates a simple half-wave or full-wave rectifier circuit first, showing its pulsating DC output. Then, a capacitor filter is added, and the teacher shows how the output becomes smoother on the oscilloscope or how the multimeter reading becomes more stable.

Pupils’ Activity: Pupils observe the experiment carefully, noting the difference in the output waveform/reading with and without the filter. They describe the smoothing effect.

Learning Point: Pupils visually understand the practical operation and effectiveness of filter circuits.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define filtration in power circuits.
2. State two purposes of filter circuits.
3. Mention three types of filter circuits.
4. Describe what happens to the output of a rectifier when a capacitor filter is connected to it.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes

Teaching Skill: Summarization

Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the importance of filters for stable DC power supplies. The teacher assigns homework: “Draw a simple circuit diagram of a half-wave rectifier with a capacitor filter and explain its operation.”

Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.

Learning Point: Pupils consolidate their understanding and prepare for further study.

Lesson Keywords

• Filtration – The process of smoothing out pulsating DC into a more stable DC.
• Ripple – The unwanted AC component remaining in the rectified DC output.
• Filter Circuit – An electronic circuit designed to remove ripple from a rectified DC voltage.
• Capacitor Filter – A type of filter circuit using a capacitor in parallel with the load to smooth DC.
• Inductor Filter – A type of filter circuit using an inductor in series with the load to smooth DC.
• LC Filter – A filter circuit combining inductors and capacitors for improved ripple reduction.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research the advantages and disadvantages of different filter types or calculate ripple factor. For those who need more support, the teacher can provide simplified diagrams and allow more time for observation and explanation during the demonstration.

Note for teachers using this lesson plan

Ensure all components for the practical demonstration are readily available and in good working condition. Emphasize safety precautions when working with electrical circuits. Encourage pupils to ask questions and participate actively.