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✦ Class 8 · Science
Light: Mirrors and Lenses
Have you ever wondered why the word 'AMBULANCE' is written backward on the front of an ambulance? We'll figure that out today!
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What this lesson covers
Step by step, in this order.
- 1Introduce the problem: choosing a car's side mirror for a wide view. This will lead to convex mirrors.
- 2Explain that light travels in straight lines and introduces reflection from smooth surfaces.
- 3Describe the activity: using a comb, a torch, and a plane mirror to show a ray of light and its reflection.
- 4Introduce the Laws of Reflection: incident ray, reflected ray, normal, angle of incidence (i), angle of reflection (r). State that angle i = angle r and all three lie in one plane.
- 5Work a numerical: If the angle of incidence is 35°, the angle of reflection is 35°. Also, calculate the angle between the ray and the mirror (90° - 35° = 55°).
- 6Describe properties of images formed by a plane mirror: erect, virtual, same size, same distance behind, and introduce lateral inversion with the AMBULANCE example.
- 7Introduce spherical mirrors: concave (curves inward) and convex (curves outward).
- 8Describe the activity: observing your image in the inside and outside of a steel spoon.
- 9Explain uses: Concave mirrors make magnified or inverted images (dentist's mirror, torch reflector). Convex mirrors make erect, smaller images and show a wider view (car side mirror, hill-road bends). This solves the initial problem.
- 10Introduce Refraction: light bending when passing from one medium to another. Describe the activity: a pencil appearing bent in a glass of water.
How it looks
A real board, not a video.
This board is from a different Science lesson — yours will look like this. She writes and draws while she explains, and stops to check you followed.
Doubts this lesson clears up
- What exactly is a 'virtual' image, and how is it different from a 'real' image?
- Why does light bend when it goes from air into water or glass? What causes that?
- How do the lenses in spectacles help people see better?
- Can a concave mirror always make things look bigger, or can it sometimes make them look upside down?
- What is the main difference between how a mirror works and how a lens works?
- Are reflection and refraction happening around us all the time, or only in special cases?
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