WAVE–PARTICLE DUALITY
Light and other electromagnetic waves exhibit wave-like characteristics through
interference and diffraction. However, as we saw in the photoelectric effect, light
also behaves as if its energy were granular, composed of particles. This is wave–
particle duality: Electromagnetic radiation propagates like a wave but
exchanges energy like a particle.
Since an electromagnetic wave can behave like a particle, can a particle of matter
behave like a wave? In 1923, the French physicist Louis de Broglie proposed that
the answer is yes. His conjecture, which has since been supported by experiment, is
that a particle of mass m and speed v—and thus with linear momentum p = mv—has
an associated wavelength, which is called its de Broglie wavelength.
Particles in motion can display wave characteristics, and behave as if they had a
wavelength λ = h/p.
Since the value of h is so small, ordinary macroscopic objects do not display
wave-like behavior. For example, a baseball (mass = 0.15 kg) thrown at a speed of
40 m/s has a de Broglie wavelength of
This is much too small to measure. However, with subatomic particles, the wave
nature is clearly evident.
Questions 6-7- Name or describe an experiment that demonstrates that light