Nelson Science Perspectives 10
1st Edition
ISBN: 9780176355289
Table of contents
Textbook solutions
All Solutions
Section 11-2: How is Light Produced?
Exercise 1
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Solution 2
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Stars are luminous while planets and moons are non-luminous.
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Planets and moons are non-luminous objects because they do not create light of their own but only reflect light from the stars of their galaxies. In our galaxy this star is called the sun and all planets and moon in our galaxy, reflect light from the sun.
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Stars are luminous because they produce light and planets and moons are not since they only reflect it.
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Stars are luminous, planets and moons are not since they do not produce light, they only reflect it.
Exercise 2
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Incandescent bulbs are insufficient sources of light because only 5$%$ to 10$%$ of the electricity passing through them is actually converted to light energy. This means that the remaining 90$%$ to $95%$ is lost as heat via infra-red radiations.
Exercise 3
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Process of producing light by passing an electric current through a gas is electric discharge.
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Electric discharge.
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The process of producing light by passage of electricity through a gas is called electric discharge.
Exercise 4
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They both work on the same principal of absorbing UV light and then releasing it as a visible light, but they differ because in the case of phosphorescence it takes time form visible light to be emitted and in the case of fluorescence visible light is being emitted immediately.
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In the case or phosphorescence light it takes time for visible light to be emitted and in the case of fluorescence visible light is emitted immediately.
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Phosphorescence and fluorescence both work on the same principal of absorbing ultraviolet light and releasing them as visible light. In fluorescence, however, this release occurs immediately while in phosphorescence this occurs gradually. The visible light emitted by phosphorescence is of low-energy, happens gradually and therefore lasts longer and such objects are often referred to as glow-in-the-dark objects because of their this ability.
Exercise 5
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$textit{a.}$, Fluorescent brighteners in detergents absorb ultraviolet light and emit white light which makes clothes look brighter and cleaner, but it has nothing to do with cleaning, it just appears cleaner.
$textit{b.}$, Detergents that consist fluorescent brighteners shoulod be avoided since the ultraviolet light is absorbed which can be dangerous while in contact with skin.
Result
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$textit{a.}$, They absorb UV light and emit white light which makes clothes to look brighter and cleaner, but they has nothing to do with cleaning.
$textit{b.}$, These detergents should be avoided since the absorbed ultraviolet light is dangerous while in contact with skin.
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a. Fluorescent brighteners in detergents do not make the clothes cleaner, these on clothes absorb ultraviolet light and emit visible light so to the eye, the clothes appear brighter and therefore look cleaner.
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b. These brighteners absorb ultraviolet light and wearing such clothes brings the human skin in contact with this radiation and therefore should be avoided if there are other options available.
Exercise 6
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Fluorescent materials work on the principal of $color{#c34632}text{absorbtion of ultraviolet light}$ and $color{#4257b2}text{emission of visible light}$, therefore when illuminated with infrared light, these objects will not glow.
Exercise 7
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Solution 2
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Usually light is generated by the conversion of one form of energy to light energy and heat energy. In chemiluminescence however, light is generated as a product of a chemical reaction and since no heat in dissipated in the production of this light, it is called as cold-light.
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Chemiluminescence is called “cold lights” since only the light is been produced, but there is no heat dissipated.
Light is usually followed by dissipation of heat since it is formed by transforming one form of energy into the energy of light.
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Because during the process only the light has been produced, there is no heat dissipated.
Exercise 8
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Solution 2
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Yes light stick will be a good source of light in a potentially explosive environment. This is because light produced in a light stick is a product of a chemical reaction and does not involve any heat or electrical spark that can be devastating in a potentially explosive environment. Light sticks are also sealed and the chemical reaction occurring inside the stick is totally concealed and does not affect the environment outside it in any way.
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Yes light stick will be a good source of light in a potentially explosive environment.
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Light stick would be a good source of light in a potentially explosive explosive environment since it produces only light, the heat is not produced and they are also sealed, therefore, chemical reactions inside of it will not react with the surrounding.
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It would be safe to use them since heat is not produced and they are completely sealed.
Exercise 9
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Some living organisms use bioluminescence as a bait to attract preys. Others use it for their safety and to attract mates during specific seasons.
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Some microorganisms use bioluminescence in order to lure prey, attract partners or for safety, protection from predators.
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Some microorganisms use bioluminescence in order to lure prey, attract partners or for safety, protection from predators.
Exercise 10
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Incandescent bulbs work on the principal of the conversion of electrical energy by $color{#c34632}text{a metallic filament}$ to light energy and heat energy, while LED bulbs work on the principal of conversion of electrical energy to light energy by a semiconductor; $color{#4257b2}text{diode}$.
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In incandescent bulbs, a maximum of 10$%$ of electrical energy is converted to light energy while the remaining is lost as heat, while LED bulbs do not generate as much heat and are therefore $color{#4257b2}text{more efficient}$.
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LED bulbs do not require a filament and are therefore more efficient than incandescent bulbs.
Exercise 11
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CFLs work by on the principal of exciting mercury atoms. These atoms are excited using an electrical current in a low pressure sealed fluorescent tube. The inside of this tube is painted with fluorescent material which emit visible light when excited mercury atoms strike it. These light sources are more efficient than incandescent bulbs but they contain mercury which requires a proper disposal by recycling and can be detrimental to the environment and its people if not done properly. Mercury is toxic in nature and can damage the brains of small children. LED bulbs work on the principal of conversion of electrical energy to light energy by a semiconductor; $color{#4257b2}text{diode}$. This does not contain mercury so can be disposed of easily, are efficient and therefore a better alternative to CFLs.
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LED bulbs do not require mercury atoms to generate light and are equally efficient.
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