Chapter Name: Reflection of Light By Different Surfaces
Activity Name: Normal to curved surface in Reflection of Light By Different Surfaces
This experiment aims to find the normal to a curved surface using a small piece of thin foam or rubber with pins placed along a straight line on its surface.
By bending the foam inwards and outwards, students can observe how the pins representing normals converge and diverge, respectively, providing insight into the behavior of concave and convex mirrors.
- Small piece of thin foam or rubber (like the sole of a slipper)
Step by Step Procedure:
- Take the small piece of thin foam or rubber.
- Insert some pins along a straight line on the foam surface, making sure they are perpendicular to the plane of the foam.
- Consider the pins as representing the normals at various points on the foam’s surface.
- Observe that when the foam is bent inwards, the pins converge at a point (Fig-13b).
- Similarly, bend the foam outwards and observe that the pins diverge from each other (Fig-13c).
- Relate this observation to the behavior of concave and convex mirrors, where the normals converge towards the center of curvature for concave mirrors and diverge for convex mirrors.
- When the foam is not bent (Fig-13a), all pins are perpendicular to the foam’s surface, representing the normal at each point.
- When the foam is bent inwards (Fig-13b), the pins converge towards a point.
- When the foam is bent outwards (Fig-13c), the pins diverge from each other.
- Handle the pins with care to avoid any injuries.
- Be gentle while bending the foam to prevent damage.
- Ensure that the pins are placed perpendicular to the foam surface for accurate observations.
Lesson Learnt from Experiment:
The experiment demonstrates how the normals on a curved surface behave differently depending on whether the surface is concave or convex. Concave mirrors, like the foam bent inwards, have normals that converge towards a point called the center of curvature.
Conversely, convex mirrors, like the foam bent outwards, have normals that diverge. This provides students with a visual understanding of the behavior of spherical mirrors and their focal points.