Chapter 5: Light and Matter
5.1 How do we experience light?
- Heat felt from sun is a form of energy.
- The energy that carries light is called radiative energy.
Energy and Power- are measure in joules.
- In astronomy used to measure total amount of energy that is transferred to skin.
Light and Colour
- Light comes in different forms called colours which can be seen through a prism in a
rainbow of colours called a spectrum.
o Recall light experiment during lecture.
- When the basic colours of the rainbow are put together they form white light. Black
occurs when there is an absence of colour.
How do light and matter interact?
- Light can interact with matter in four basic ways:
o reflection/scattering- rebounds in a particular direction or rebounds in scattered
- Materials that transmit light are said to be transparent, and materials that absorb light are
called opaque. They are neither opaque nor transparent; they can also affect different
colours of light differently.
o Ex. Red glass transmits red light but absorbs other colors. A green lawn reflects
(scatters) green lights but absorbs all other colours.
- Interaction between light and matter determine the appearance of everything we see.
5.2 Properties of Light
What is Light?- Newton guessed that light is made of tiny particles. Light can act either like a
wave or particle.
- Waves: a pattern of motion that can carry energy without carrying matter along with it. It
is revealed by its interaction with other particles.
o Characterized by three properties:
o Wavelength- the distance between two wave peaks o Frequency- the number of times per second that a wave vibrates up and dowm
o Wave speed= wavelength x frequency
- Light- electromagnetic waves
o Light wave is a vibration of electric and magnetic fields
o Light interacts with charged particles through these electric magnetic fields
- Therefore, light can be defined as an electromagnetic wave with individual pieces
called photons. Each photon has a precise wavelength, frequency and energy.
Energy of photon depends on colour.
- Wavelength and frequency: the shorter the frequency, the higher the wavelength and
- Electromagnetic Spectrum- light that our eyes can’t see can be made visible through
electromagnetic spectrum. Includes radio waves, microwaves, infrared light, ultraviolet
rays, x-rays and gamma rays.
o Atomic Structure: atoms consist of nucleus made from positively charged protons
which has a charge of 1
o Neutrons with no charge
o Electrons negative charge -1
- Electrical charge is found within the nucleus
- Atomic Terminology:
o Atomic number: number of protons
o Atomic mass number: number of protons and neutrons
o Isotopes: same number of protons but different number of neutrons
o Molecules: material substances is far greater than the number of chemical
elements of atoms
o Compounds: composed of molecules with two or more different types of atoms
5.3 Phases of Matter:
- Solid, Liquid, Gas. Phases of the same material behave differently because of the
differences in the chemical bonds: interactions between electrons that hold the atoms in a
- Phase Changes: at very high temperatures molecular dissociation occurs, which is when
molecules split into pieces.
o Ionization- stripping of electrons, changing atoms into plasma
o Dissociation- breaking of molecules into atoms
o Evaporation- breaking of flexible chemical bonds, changing into solid
o Melting- breaking of rigid chemical bonds, changing solid into liquid
Phases and Pressure: of a substance depends on both temperature a