| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: understand that, for a point outside a spherical conductor, the charge on the sphere may be considered to be a point charge at its centre |
Learning Objective/s:
- Explain why excess charge resides only on the surface of a conductor in electrostatic equilibrium.
- Apply Gauss’s law to derive the electric field outside a spherical conductor.
- Use the point‑charge model to calculate the field at any external point.
- Predict how several spherical conductors can create a region of uniform electric field.
- Identify and correct common misconceptions about charge distribution in conductors.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Metallic sphere (demonstration object)
- Printed worksheet with Gaussian‑surface diagram
- Scientific calculators
- Student handouts summarising key formulas
- Clicker/online quiz system for misconceptions check
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Introduction:
Begin with a quick poll asking where students think charge resides in a charged metal ball. Link their responses to prior knowledge of electrostatic equilibrium and state that by the end of the lesson they will be able to treat the sphere as a point charge for any external point.
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Lesson Structure:
- Do‑now (5'): MCQ on charge distribution; teacher reviews answers (checks prior knowledge).
- Mini‑lecture (10'): Review conductors, introduce Gauss’s law, derive E = kQ/r² for r > R.
- Guided demonstration (8'): Show metallic sphere, draw a Gaussian surface, discuss symmetry and field direction.
- Worked example (12'): Solve the sample problem together, students calculate the field 5 cm above the surface.
- Group activity (10'): Students complete worksheet applying the point‑charge model to a new sphere and sketch the field lines.
- Misconception check (5'): Clicker quiz addressing common errors listed in the source.
- Summary & exit ticket (5'): Students write one key takeaway and answer a short question on when the point‑charge model is valid.
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Conclusion:
Recap that a spherical conductor behaves like a point charge for any external observation point, reinforcing the link to Gauss’s law. Collect exit tickets to gauge understanding, and assign homework: calculate the field for a different charged sphere and explain why the model fails if the observation point is inside the conductor.
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