Introduction to Light and Optics

Study Notes

The science that studies light and its interaction with matter
Helps us understand the nature of colors
Allows us to design optical devices like microscopes, telescopes, lenses, and cameras
Used in developments like lasers and optical fibers

Light has two different natures, acting like a particle and a wave.
Particle Theory (Corpuscular Theory of Light)
- States that light is composed of tiny particles called photons, which are emitted in all directions from a source.
Wave Theory
- Proposed by Christiaan Huygens, stating that light is emitted in all directions as a series of waves in a medium called luminiferous ether
Electromagnetic Wave Theory
- James Clerk Maxwell discovered that self-propagating electromagnetic waves travel through space at a constant speed, equal to the previously measured speed of light.
- Maxwell concluded that light is a form of electromagnetic radiation.

A reflection occurs when an object is placed in front of a mirror.
With two mirrors, a single source of light can be reflected multiple times, until the intensity of the light becomes low.
The number of images of an object placed between two mirrors can be calculated by:
- Number of Images = 360° / angle between mirrors) - 1
As the angle between the mirrors decreases, the number of images increases.

The Angle of Incidence: the angle between an incident ray on a surface and the line perpendicular to the surface at the point of incidence (called the normal).
The Angle of Reflection: the angle between a reflected ray and the normal drawn at the point of incidence to a reflecting surface.

The wave nature of light is needed to explain various phenomena like interference, diffraction, and polarization.

Light waves interfere with each other much like mechanical waves do
Interference occurs when the electric and magnetic fields of two or more light waves interact, adding together to give a new wave.

For sustained interference between two sources of light, two conditions must be met:
- The sources must be coherent, meaning they maintain a constant phase with respect to each other.
- The waves must have identical wavelengths

Two sources are said to be coherent if they emit light waves of the same frequency, amplitude, and always in phase with each other.

Light from a monochromatic source is allowed to pass through a narrow slit.
The light from the single slit is allowed to fall on a screen containing two narrow slits.
Lasers are commonly used as coherent sources, producing intense, coherent, monochromatic beams that can be used to illuminate multiple slits directly.

Thomas Young first demonstrated interference in light waves from two sources in 1801.
Light is incident on a screen with a narrow slit (So).
Light waves emerging from this slit arrive at a second screen that contains two narrow, parallel slits (S1 and S2).