Lesson Plan

• Describe the relationship between solenoid turns, current, and magnetic field.
• Explain how inserting a ferrous core changes the magnetic field and why.
• Calculate the magnetic field inside a solenoid with and without a ferrous core.
• Analyse the effect of core permeability and saturation on field strength.

• Projector or interactive whiteboard
• Calculator or spreadsheet software
• Solenoid model with interchangeable air and ferrous cores (or simulation)
• Worksheet with practice problems
• Diagram handout of solenoid and field lines
• Ruler/Measuring tape (if using physical demo)

Begin with a quick demonstration: energize a long solenoid and show the weak magnetic field using a compass. Recall the formula B = μ₀ n I for an air‑core solenoid and discuss how we will evaluate its strength. Today’s success criteria: students will predict and compute the field increase when a ferrous core is inserted.

1. Do‑now (5 min): Students answer a short question on the direction of magnetic field lines inside a solenoid.
2. Mini‑lecture (10 min): Review the air‑core solenoid formula and introduce permeability (μ = μ₀μᵣ).
3. Demonstration (8 min): Compare a solenoid with an air core and one with a ferrous core using compasses; discuss observed differences.
4. Guided calculation (12 min): Work through the example calculation from the notes, students complete each step on a worksheet.
5. Practice problems (10 min): Pairs solve the provided questions; teacher circulates to provide feedback.
6. Check for understanding (5 min): Exit ticket – write the factor by which the field changes for a given μᵣ.

Summarise that a ferrous core multiplies the solenoid’s field by its relative permeability, though saturation can limit growth. For the exit ticket, each student records the factor for μᵣ = 500. Homework: complete the remaining practice questions and reflect on how core material choice affects electromagnet design.