2. THEORIES OF LIGHT Is light a wave or a stream of particles?
Let’s first analyze characteristics behaviors of light as a wave:
All waves are known to undergo reflection or the bouncing off of an obstacle.

3. All waves are known to undergo refraction when they pass from one medium to another medium.
Diffraction involves a change in direction of waves as they pass through an opening or around an obstacle in their path.

4. Wave interference is a phenomenon that occurs when two waves meet while traveling along the same medium.
Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming un-polarized light into polarized light is known as polarization.

5. Now what about the particle-like behavior?

6. The photoelectric effect is observed when light of a certain frequency strikes a metal and ejects electrons.

7. Interference Phenomenon Photoelectric effect
Can be explained in terms of waves.
Can be explained in
terms of particles.
Reflection
                
            
Refraction
Interference
Diffraction
Polarization
Photoelectric effect
               

8. THEORIES OF LIGHT
Newton's theory - light consists of particles called corpuscles; this theory only explained reflection and refraction.
Wave theory of light (Maxwell's theory) - light behaves like a wave; this explained all the properties of light such as reflection, refraction, diffraction, interference and polarization; it did not explain the photoelectric effect or radiation produced by an incandescent light.
Quantum theory - light has a dual nature: when light is transmitted through space or matter, it behaves like a wave; when light is emitted or absorbed, it behaves like a particle called a photon.

9. ELECTROMAGNETIC WAVES
Electromagnetic waves are waves that are capable of traveling through a vacuum. They consist of oscillating electric and magnetic fields with different wavelengths. The wave speed equation is: c = f λ
 where c is the speed of light.

10. The Electromagnetic Spectrum 

11. Wavelengths