Chapter 5.docx

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Astronomy & Astrophysics
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Ian Shelton

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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 emission o absorption o transmission o reflection/scattering- rebounds in a particular direction or rebounds in scattered direction. - 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 energy. - 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 molecule together. - 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
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