Properties of Light

Frequency and Energy

• Light waves carry energy (E) across space.
• The energy is related to the frequency of the light wave by

• E = hf
• where h = Planck’s constant

• Recall that wave speed relates frequency and wavelength: v = f
• and for light, c = f
• so, E  f or E  1/

Creating and Detecting Light

• Light is created by the motion of charged particles.
• Matter is made up of atoms, which are in turn made up of charged particles.
• Motions of these charged particles create light.
• Not just the light we detect with our eyes, but at all wavelengths (or frequencies).

Electromagnetic Spectrum

Properties of Light

• Polarization
• Reflection
• Refraction
• Dispersion
• Diffraction
• Interference

Properties of Light: Reflection and Refraction

• An isolated light beam travels in a straight line.
• Light can change directions under certain conditions:
• Reflection from a surface,
• mirrors, objects
• Refraction (or bending of a ray of light) as the ray travels from one transparent medium to another.
• pencil in a clear glass of water
• light through a piece of glass

Properties of Light: Dispersion

• Electromagnetic waves interact with the charged particles in matter and travel more slowly in transparent media than in a vacuum.
• The change in speed of the light wave causes the wave to refract.
• Since the speed of an EM wave in a medium changes with wavelength, the amount of refraction depends on the wavelength.
• This effect is called dispersion.