Waves · SHS1 Physics

Lesson notes

Learning Objectives

Indicator: 1.2.2.LI.3 - Determine the number of images formed by inclined mirrors.

By the end of the lesson, learners can:

Set up two plane mirrors at given angles of inclination (30°, 45°, 60°) and count the number of images formed of a single object.
Apply the formula N = (360/θ) - 1 to calculate the number of images formed when two plane mirrors are inclined at an angle θ.
Compare counted image numbers with calculated values and account for any discrepancies observed.
Predict the number of images formed for any angle of inclination between two plane mirrors, including angles not tested experimentally.
Justify the relationship between the angle of inclination and the number of images formed using the principle of successive reflections.

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Curriculum details

Strand: Energy (Strand 2)
Sub-strand: Waves (2.2)
Content standard: 1.2.2.CS.1 - Demonstrate knowledge and understanding of reflection on plane mirrors 1.2.2.LO.1 Explain the formation of images in plane mirrors
Indicator: 1.2.2.LI.3 - Determine the number of images formed by inclined mirrors.
Suggested placement: Semester 1, Week 18 (Week 18 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: NaCCA curriculum document, p. 52

Exemplars (from the NaCCA curriculum)

Provide learners in mixed-ability groups with 2 mirrors and let them incline to each other to observe the no. of images formed.
- Let learners incline the mirrors at 30 , 45 , 60 and record the number of images in each case. o o o
- Let learners divide 360 by the angle of inclination and subtract 1 from the resultant.
- Let learners compare their values in exemplars 1 and 2 and come out with a formula for determining the no. of images.
Foster an inclusive and respectful classroom culture and address bias in teaching materials and examples.
Assessment (1.2.2.AS.3). The document marks these depth-of-knowledge levels for this indicator: Level 3 Strategic reasoning.
Teaching and Learning Resources:
- Plane mirror strip with holder,
- Drawing boards,
- Optical pins,
- A4 sheets,
- Ruler,
- Protractor,
- Thumb tugs/drawing pins