Analyzing Activity 10.7: Solar Concentrator
Scenario: You hold a concave mirror facing the sun and focus the light on a paper.
Physics Involved:
- Sunlight reaches Earth as parallel rays (because the Sun is very far away).
- A Concave Mirror is a converging mirror.
- It reflects these parallel rays to a single point called the Principal Focus.
- The concentration of many light rays at one tiny point generates intense heat.
- This heat is sufficient to reach the ignition temperature of the paper, causing it to burn.
Why didn’t the Convex Mirror work? In Activity 10.11, replacing the concave mirror with a convex one failed to burn the paper. This is because a convex mirror diverges (spreads out) light. It does not concentrate energy; it scatters it.
Analyzing Activity 10.8: The Water Drop Lens
Scenario: A drop of water on a text makes the letters look bigger.
Physics Involved:
- Surface Tension pulls the water drop into a curved shape.
- The top surface bulges outwards, making it thick in the middle and thin at the edges.
- This shape corresponds to a Convex Lens.
- When the object (text) is very close to a convex lens (closer than its focal length), the lens forms a Virtual, Erect, and Enlarged image.
- This is the basic principle of a simple microscope or magnifying glass.
Sample Problem
Problem: A shopkeeper wants to install a mirror to watch over his entire large shop from a single point at the cash counter. Which mirror should he choose and why?
Solution: He should choose a Convex Mirror.
- Field of View: Convex mirrors reflect light outwards, allowing them to capture images from a much wider angle than plane or concave mirrors.
- Orientation: They always produce an erect (upright) image. A concave mirror might produce an inverted image if the customer is far away, which would be confusing.
- Conclusion: Even though the image is smaller (diminished), the ability to see the whole shop erect makes the convex mirror the best choice for surveillance.