Light has a dual nature because it can behanve like a particle or as a wave depending on the circumstances.
Light is part of the electromagnetic spectrum of waves and the theory of EM waves predicted the existence of light beyond the visible spectrum. It was thought that all aspects of physics could be explained fully using just Newton's laws of motion and Maxwell's theory of EM waves, scientists at the time thought photoelectricity would be explained later.
Photoelectricity was explained when Einstein brought forward the theory that light consists of photons that are 'particle-like' packets of em waves.
Hence, light has a dual nature.
- Wave-like nature of light
observed during the diffraction of light
the light emerging after passing through a narrow spilt spreads out
the narrower the gap or the longer the wavelength the greater the amount of diffraction
- Particle-like nature of light
observed during the photoelectric effect
light directed at a metal surface
a surface electron absorbs a single photon (frequency f)
the kinetic energy of the electron is increased by…