| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: Explain why the outer casing of an electrical appliance must be either non-conducting (double-insulated) or earthed |
Learning Objective/s:
- Describe why a live outer casing can cause electric shock.
- Explain the two safety design approaches: double‑insulation and protective earthing.
- Compare construction, fault protection, and typical applications of double‑insulated versus earthed appliances.
- Apply Ohm’s law and the voltage‑divider concept to evaluate shock risk.
- Identify the regulatory symbols for double‑insulated and earthed appliances.
|
Materials Needed:
- Projector and screen
- Printed handout with diagrams and comparison table
- Sample appliances (e.g., hair dryer, metal toaster)
- Earth‑continuity tester or multimeter
- Worksheet for group activity
- Exit‑ticket slips
|
Introduction:
Begin with a short video showing a person receiving a shock from a faulty appliance to capture interest. Ask students what they already know about why metal casings can be dangerous. Explain that by the end of the lesson they will be able to state the safety reasons for double‑insulation or earthing and identify the correct symbols.
|
Lesson Structure:
- Do‑now (5'): Quick written response to “What could happen if the outer case of a metal toaster becomes live?” – collect responses for a quick check.
- Mini‑lecture (10'): Review fault current, Ohm’s law (I = V/R), and the voltage‑divider equation for casing voltage. Highlight safety limits (<50 V).
- Demonstration (10'): Show a double‑insulated hair dryer and a metal toaster connected to an earth wire; use the tester to illustrate continuity and fault current paths.
- Group activity (12'): In pairs, complete a comparison table (construction, fault protection, applications, symbols). Teacher circulates to clarify.
- Guided practice (8'): Solve a problem calculating Vcasing for a given fault voltage and resistances.
- Check for understanding (5'): Two‑question exit ticket – one conceptual, one numerical.
|
Conclusion:
Recap the two safe design approaches and why each prevents dangerous shock. Collect exit tickets to gauge mastery and assign a short homework: research one household appliance and state whether it is double‑insulated or earthed, citing the identifying symbol.
|