Sources of Direct Current

Grade 12 · Physics

Semester 1 | Period 2 | Week 7

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Subject: Physics

Semester: 1

Period: 2

Week: 7

School Name:

Teacher’s Name:

Subject: Physics

Grade Level: Grade 12

Week & Period: Week 7, Period II

Date:

Topic: Sources of Direct Current
Sub-topics:

  • Primary and Secondary Cells
  • Fuel Cells and Solar Cells

Learning Objectives:

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

  1. Identify different sources of direct current (DC).
  2. Distinguish between primary and secondary cells.
  3. Describe the working principles of fuel cells and solar cells.
  4. Compare the advantages and limitations of each DC source.
  5. Perform a simple test on a cell to check its output.

 

Instructional Materials:

  • Dry cell (e.g. AA battery)
  • Lead-acid accumulator (secondary cell)
  • Solar panel (mini size)
  • Simple fuel cell demo kit or diagram
  • Multimeter
  • Copper and zinc plates
  • Lemon or vinegar (for a DIY cell)
  • Bulb, connecting wires, and resistors

 

Anticipation (Warm-Up):

Ask students:

  • “What powers your flashlight?”
  • “Why do phone batteries need recharging?”
    Let them brainstorm different devices powered by batteries or sunlight.

 

Building Knowledge (Main Lesson):

  1. What is Direct Current (DC)?
  • DC is electric current that flows in one direction.
  • Supplied by batteries, solar panels, and some generators.

 

  1. Types of DC Sources
  2. Primary Cells (non-rechargeable):
  • Example: Dry cell (zinc-carbon)
  • Provide current through chemical reactions that cannot be reversed.
  • Once exhausted, they are discarded.
  • Equation: Zn + 2MnO₂ → ZnO + Mn₂O₃
  1. Secondary Cells (rechargeable):
  • Example: Lead-acid battery, lithium-ion battery
  • Chemical reactions are reversible.
  • Used in cars, phones, inverters.
  1. Fuel Cells:
  • Produce electricity through chemical reaction between hydrogen and oxygen.
  • Clean energy but expensive.
  • Equation: 2H₂ + O₂ → 2H₂O + electrical energy
  1. Solar Cells:
  • Convert light energy directly into electricity using photovoltaic effect.
  • No moving parts, eco-friendly.
  • Efficiency depends on sunlight.

 

Activities / Demonstration:

  1. Multimeter Voltage Testing:
  • Measure voltage of a dry cell, a lead-acid accumulator, and a solar cell under the sun or bulb.
  1. DIY Battery (Lemon Battery):
  • Materials: lemon, copper wire, zinc nail, wires, bulb
  • Procedure: Insert copper and zinc into lemon, connect bulb—observe glow
  • Observation: Current is generated through a chemical reaction in lemon.
  1. Solar Panel Demonstration:
  • Connect small solar panel to LED or buzzer.
  • Place under bright light or sun.
  • Observe the output.

 

Sample Calculation:

Q: A dry cell provides 1.5V and delivers a current of 0.3A for 5 hours.
Find: Total energy supplied.
Solution:
Energy = Power × Time = (V × I) × t
= (1.5 × 0.3) × (5 × 3600)
= 0.45 × 18000 = 8100 Joules

 

Assessment Questions:

  1. Objective Questions
  • What distinguishes a primary cell from a secondary cell?
  • Which of these is not a source of DC?
    A. Dry cell
    B. Solar panel
    C. Alternator
    D. Lead-acid battery
  1. Short Answer Questions
  • State two advantages and two disadvantages of solar cells.
  • Why do fuel cells not require recharging?
  1. Problem Solving
    A battery rated 12V delivers 3A for 2 hours.
    i. Calculate the energy supplied in joules.
    ii. What is the total charge delivered?

 

Homework:

  • Write a report comparing primary and secondary cells. Include three uses each.
  • Draw and label a simple diagram of a solar cell and a lead-acid battery.

 

Expanded Notes:

  • Batteries are portable energy sources; useful in remote areas.
  • Solar energy is sustainable but affected by weather.
  • Fuel cells are ideal for future clean energy systems.
  • Proper disposal of batteries is necessary to avoid environmental pollution.

 

Differentiation:

  • Visual learners: Use diagrams and demos
  • Kinesthetic learners: Conduct simple circuit testing
  • Support weaker learners with printed notes and oral follow-up

 

Teacher’s Reflection:

  • Were students able to identify and differentiate all four DC sources?
  • Did the practical demos spark interest and improve understanding?
  • Should any topic be revised next class before moving into Ohm’s Law?