Learning Objectives
- Understand reflection of light and laws of reflection
- Learn about plane mirrors and image formation
- Know about spherical mirrors and lenses
- Understand dispersion of light and rainbow formation
Key Concepts
Reflection of Light
Reflection: Bouncing back of light from a surface. All surfaces reflect light (smooth surfaces give regular reflection, rough surfaces give diffused/irregular reflection).
Laws of Reflection:
- The angle of incidence is equal to the angle of reflection (ā i = ā r).
- The incident ray, reflected ray, and normal all lie in the same plane.
Image formed by Plane Mirror
- Image is virtual (cannot be obtained on screen) and erect (upright).
- Image is of the same size as the object.
- Image is at the same distance behind the mirror as object is in front.
- Image is laterally inverted (left appears right and vice versa).
Spherical Mirrors
Concave mirror: Reflecting surface curves inward. Used in torches, headlights, shaving mirrors, dentist mirrors. Converges light.
Convex mirror: Reflecting surface curves outward. Used in rear-view mirrors of vehicles. Diverges light, gives wider field of view.
Lenses
Convex lens (converging): Thicker in middle. Used in magnifying glass, spectacles for farsightedness.
Concave lens (diverging): Thinner in middle. Used in spectacles for nearsightedness.
Sunlight and Colours
White light is made up of seven colours: VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
Dispersion: Splitting of white light into its component colours by a prism.
Rainbow: Formed by dispersion of sunlight by tiny water droplets in the atmosphere after rain.
Summary
Light reflects following the laws of reflection. Plane mirrors form virtual, erect, same-size, laterally inverted images. Concave mirrors converge light; convex mirrors diverge it. Convex lenses converge; concave lenses diverge. White light splits into VIBGYOR through a prism (dispersion).
Important Terms
- Reflection: Bouncing back of light from a surface
- Lateral inversion: Left-right reversal in mirror image
- Concave mirror: Converging mirror (inward curve)
- Convex mirror: Diverging mirror (outward curve)
- Dispersion: Splitting of white light into colours
Quick Revision
- ā i = ā r (Law of reflection)
- Plane mirror: virtual, erect, same size, laterally inverted
- Concave = converges, Convex = diverges
- White light = VIBGYOR (7 colours)
- Rainbow: sunlight + water droplets ā dispersion