Wave Particle Duality

Question 1

Where is light’s wave like nature?

Answer 1

• Wave like nature is observed when diffraction of light takes place.
• The light emerging from the slit spreads out in the same way as the water waves spread out after passing through a gap.
• The narrower the gap or the longer the wavelength the greater the amount of diffraction.

Question 2

When is particle like nature observed?

Answer 2

• The photoelectric effect.
• When light is directed at a metal surface and an electron at the surface absorbs a photon of frequency of f, the kinetic energy of the electron is increased from a negligible value by hf.• The electron can escape if the energy it gains from a photon exceeds the work function of the metal.

Question 3

What was De Broglie’s hypothesis?

Answer 3

• Matter particles have a dual wave particle nature
• Wave like behavior of a matter particle is characterized by a wavelength, its de broglie wavelength, which is related to momentum:
λ = h / mv
h = planck’s constant.

Question 4

Where is the evidence from the de broglie’s hypothesis?

Answer 4

• A narrow beam of electrons in a vacuum tube is directed at a thin metal foil, a metal is composed is many tiny crystalline regions, each region of grain consists of positive ions arranged in fixed positions in rows in a regular pattern, the rows of atoms cause the electrons in the beam to be diffracted, as a beam of light is diffracted when it passes through a slit.
• Electrons in the beam pass through the metal foil and are diffracted in certain directions only, they from patterns of rings on fluorescent screen at the end of the tube. Each ring is due to electrons diffracted by the same amount from grains of different orientations at the same angle to the incident beam.