LCD AND LED - LCD stands for “liquid crystal display” and technically, both LED and LCD TV’s are liquid crystal displays. The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light. LED, which stands for “light emitting diodes,” differs from general LCD TV’s in that LCD’s use fluorescent lights while LED’s use those light emitting diodes. LED TV’s provide a better picture.

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LCD and LED

What’s the difference between LCD and LED?

BY HOWSTUFFWORKS.COM CONTRIBUTORS

LCD stands for “liquid crystal display” and technically, both LED and LCD TV’s are liquid crystal displays.

The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light.

So really, LED TV's are a subset of LCD TV's.

LED, which stands for “light emitting diodes,” differs from general LCD TV's in that LCD's use fluorescent lights while LED's use those light emitting diodes.

Also, the placement of the lights on an LED TV can differ.

The fluorescent lights in an LCD TV are always behind the screen.

On an LED TV, the light emitting diodes can be placed either behind the screen or around its edges.

The difference in lights and in lighting placement has generally meant that LED TV's can be thinner than LCD's, although this is starting to change.

It has also meant that LED TV's run with greater energy efficiency and can provide a clearer, better picture than the general LCD TV's.

LED TV's provide a better picture for two basic reasons.

First, LED TV's work with a color wheel or distinct RGB-colored lights (red, green, blue) to produce more realistic and sharper colors.

Second, light emitting diodes can be dimmed.

The dimming capability on the back lighting in an LED TV allows the picture to display with a truer black by darkening the lights and blocking more light from passing through the panel.

This capability is not present on edge-lit LED TVs; however, edge-lit LED TV's can display a truer white than the fluorescent LED TV's.

Because all these LCD TV's are thin-screen, each has particular angle-viewing and anti-glare issues.

The backlit TV's provide better, cleaner angle viewing than the edge-lit LED TV.

However, the backlit LED TV will usually have better angle viewing than the standard LCD TV.

Both LED and LCD TVs have good reputations for their playback and gaming quality.

https://electronics.howstuffworks.com/difference-between-lcd-and-led.htm

LITMUS PAPER - The word "litmus" comes from the old Norse word for "to dye or color". The blue dye has been extracted from lichens since the 16th century. The first known use of litmus was around 1300 AD by Spanish alchemist Arnaldus de Villa Nova. Litmus paper turns red in response to acidic conditions (pH 7). When the pH is neutral (pH = 7) then the dye is purple. While litmus paper is most often used to test the pH of liquids, it can be used to test gases if the paper is dampened with distilled water before exposure to the gas.

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Litmus Paper

What Is Litmus Paper? Understand the Litmus Test

Litmus Paper and the Litmus Test

by Anne Marie Helmenstine,Ph.D

You can make paper test strips to determine the pH of an aqueous solution by treating filter paper with any of the common pH indicators. 

One of the first indicators used for this purpose was litmus. 

Litmus paper is paper that has been treated with a specific indicator - a mixture of 10-15 natural dyes obtained from lichens (mainly Roccella tinctoria) that turns red in response to acidic conditions (pH 7).

When the pH is neutral (pH = 7) then the dye is purple.

The first known use of litmus was around 1300 AD by Spanish alchemist Arnaldus de Villa Nova.

The blue dye has been extracted from lichens since the 16th century.

The word "litmus" comes from the old Norse word for "to dye or color".

While all litmus paper acts as pH paper, the converse is untrue. It's incorrect to refer to all pH paper as "litmus paper".

Fast Facts: Litmus Paper

·       Litmus paper is a type of pH paper made by treating paper with natural dyes from lichens.

·       The litmus test is performed by placing a small drop of sample onto the colored paper.

·       Usually, litmus paper is either red or blue. Red paper turns blue when the pH is alkaline, while blue paper turns red when the pH turns acidic.

·       While litmus paper is most often used to test the pH of liquids, it can be used to test gases if the paper is dampened with distilled water before exposure to the gas.

Litmus Test

To perform the test, simple place a drop of liquid sample on a small strip of paper or dip a piece of litmus paper in a small specimen of the sample.

Ideally, you don't dip litmus paper in an entire container of a chemical. The reason is that the dye could contaminate a potentially valuable sample.

The litmus test is a quick method of determining whether a liquid or gaseous solution is acidic or basic (alkaline).

The test can be performed using litmus paper or an aqueous solution containing litmus dye.

Initially, litmus paper is either red or blue. The blue paper changes color to red, indicating acidity somewhere between the pH range of 4.5 to 8.3 (however, note 8.3 is alkaline). 

Red litmus paper can indicate alkalinity with a color change to blue. In general, litmus paper is red below pH of 4.5 and blue above a pH of 8.3.

If the paper turns purple, this indicates the pH is near neutral. Red paper that does not change color indicates the sample is an acid.

Blue paper that does not change color indicates the sample is a base.

Remember, acids and bases only refer to aqueous (water-based) solutions, so pH paper won't change color in non-aqueous liquids, such as vegetable oil.

Litmus paper may be dampened with distilled water to give a color change for a gaseous sample.

Gases change the color of the entire litmus strip, since the whole surface is exposed. Neutral gases, such as oxygen and nitrogen, do not change the color of the pH paper.

Litmus paper that has changed from red to blue can be reused as blue litmus paper. Paper that has changed from blue to red can be reused as red litmus paper.

Limitations of the Litmus Test

The litmus test is quick and simple, but it suffers a few limitations.

First, it's not an accurate indicator of pH. It does not yield a numerical pH value.

Instead, it roughly indicates whether a sample is an acid or a base.

Second, the paper can change colors for other reasons besides an acid-base reaction.

For example, blue litmus paper turns white in chlorine gas. This color change is due to bleaching of the dye from hypochlorite ions, not acidity/basicity.

Alternatives to Litmus Paper

Litmus paper is handy as a general acid-base indicator, but you can get much more specific results if you use an indicator that has a more narrow test range or that offers a wider color range. 

Red cabbage juice, for example, changes color in response to pH all the way from red (pH = 2) through blue at neutral pH to greenish-yellow at pH = 12, plus you are more likely to find cabbage at the local grocery store than lichen.

The dyes orcein and azolitmin yield results comparable to those of litmus paper.

Anne Marie Helmenstine, Ph.D.

·   Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

·   Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

·   ThoughtCo and About Education chemistry expert since 2001.

·   Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

Anne Marie Helmenstine, Ph.D.

​ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/what-is-litmus-paper-3976018

HYDROLOGY - Hydrologists are a large and diverse group. They are dedicated to the preservation of the Earth's water by any means necessary. Hydrologists work to keep our ground water safe. Other hydrologists research pollution levels in snow, soil and even glaciers.Hydrologists will go pretty far to get information on the movement of water. Hydrologists help maintain the livelihood of mankind by helping to regulate floods, pollution and sewage. They get to make some really fascinating models. Hydrology is a branch of science that will always be in demand, especially as our population continues to grow and the demand for fresh water increases.

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Hydrology

How Hydrology Works

BY JENNIFER POCOCK

Water -- We drink it, we bathe in it, and we play in it.

Water gives us life, yet too much or too little can also take life away.

It's the most common substance on Earth, but far too often there's not a drop to drink.

Water's extraordinary attributes give life to this planet, which might otherwise be barren and lifeless.

For example, water actually expands when it freezes, becoming less dense. If ice didn't float on water, our planet would be a very different place today.

Ice would sink to the bottoms of lakes and rivers, where the sun would be unable to melt it in the spring, a necessary process for making clouds and rain, which continue the flow of the cycle.

This would happen every year until, eventually, there was nothing left but ice and an uninhabitable wasteland.

Water exists in three states -- solid, liquid and gas -- which comprise the Earth's hydrologic cycle, better known as the water cycle.

In this cycle, fresh water comes to Earth as rain, sleet, snow and hail, pouring down over oceans and land day and night.

The water that hits land runs off into larger bodies of water, like lakes and rivers, or it seeps underground and becomes groundwater, nourishing our crops in the process.

When the sun comes back out, it heats up the water and makes vapor, which rises up and condenses into clouds, which gather, become heavy with water and fall back to Earth as rain.

Thi­s cycle has gone on since the world began and has made life on Earth possible.

In fact, there is no more and no less water in the world today than there was when the dinosaurs were around.

Think of the Earth's water cycle as the ultimate recycling method. No wonder hydrologists are so fascinated by it.

Go to the next page to read about the different branches of science that hydrologists make use of to study the Earth's water cycle.

FEELING A BIT PARCHED?

While about 70 percent of the Earth's surface is covered with water, 97 percent of the water is salty ocean water, which is unfit for human consum­ption.

Of the 3 percent that's fresh water, 2 percent is frozen into glaciers, leaving only 1 percent of the entire world's water supply fit to drink. Think of that the next time you take a really long shower.

Hydrologists

Hydrology is the study of the flow of water through the hydrologic cycle, and Hydrologists are the people conducting the research.

While most people don't think much about water, hydrologists examine every aspect of it -- where it comes from and in what quantities, where it goes, how it gets there and what happens to it in the process.

To do this, they use a lot of math and some really cool gadgets, and they even get a little wet sometimes. The results are astounding.

Hydrologists help designers and engineers construct dams and levees to keep towns safe from flooding, track pollution and find new water sources -- they even help track water in space.

Because water is everywhere and is so critical to nearly everything we do, hydrologists span almost every branch of science, from physics and geology to astronomy and ecology.

There are so many ways to study the Earth’s waters; here are just a few.

Spatial hydrology is the study of the movement of the waters of the Earth through the hydrologic cycle using a spatial database developed in a geographic information system (GIS). This means that they try to connect the varying space that is the land with the varying time and flow that is the water ^{[source: Purdue University].}

Hydrogeology, or groundwater hydrology, tracks the flow of water through the soil and into underground systems. 

Hydrogeologists help find underground sources of water (aquifers) that we can tap into for drinking water.

They monitor these, as well as the flow of water into underground sites to determine how much is taken out.

They also figure out how water flows through soil. This may sound boring, but if you're a farmer who needs the right amount of soil moisture to grow your crops, it's vital information.

Hydrogeologists help with irrigation practices and monitor pollution that seeps down through the soil into our wells.

Vadose zone hydrology is a subset of hydrogeology that focuses on the layer of earth directly above an aquifer, called the vadose zone.

This zone is important because it acts as a final filter and aeration device before rain becomes groundwater, which is sometimes taken straight from the ground through wells and used without purification methods.

If the vadose zone is unhealthy, so is much of our drinking water.

Hydraulics has nothing to do with making your car do really cool tricks (well, it does, just not in this context).

This is the study of the physical flow of water. Hydraulics professionals use mathematical modeling to track the flow of water from one source to another.

The major purpose of this is to track not the water but contaminants in it.

For example, if a factory is dumping industrial waste into a river, it will flow downstream and eventually get dispersed into the ocean.

Who knows where it will end up? The people who study hydraulics do.

Hydrometeorology, also known as hydroclimatology, uses meteorological instruments to figure out how much rain will fall and in what specific areas.

This is useful for many reasons -- not just so you know when to take your umbrella when leaving the house.

Hydrometeorology can help determine how much water will reach one area in a given year. This helps with the building of flood-control devices and irrigation systems.

In a form of science known as dendrohydrology, dendrohydrologists use tree rings to help determine historical rainfall and drought conditions, stream flow, runoff, and much more.

Knowing this information can help regions without reliable historical records predict the hydrological future.

If the world's water supply contains the same amount of water today as it did in the beginning, then how is it possible to waste water?

Won't it just come back? Why do people fight over water? Find out on the next page.

HYDROLOGY IN THE MILITARY

Hydrologists don't just do things like controlling floods and water pollution. NASA has a hydrology program that maps the oceans from outer space.

Other programs around the U.S. prepare hydrological reports on the consequences to an area's water supply if a weapon of mass destruction were used in the region.

These reports can be used to help clear up the fallout from an attack, or, on the other hand, they can indicate a way to take away a nation's water supply [source: Global Security].

Water Supply Control and Pollution Control

While the Earth still has the same amount of water it has always had, the demand for water is greater than ever.

The population keeps growing, and everyone needs to be fed and clothed with materials that have to be grown using water.

The same people need to live in houses built with steel, lumber, or other various building materials -- again, these materials take a large amount of water to manufacture or grow.

Of course, people also have to bathe and wash their clothes and go to the bathroom … all of this takes water.

You want to know the real kicker? Water doesn't fall evenly over the entire Earth. One place may get too much rain, causing floods and devastation, while another might get very little, causing a drought.

Once the water goes down the drain, it takes a while for it to be processed back into something that can be used again.

If there is not enough rainfall for your area and the population uses too much water, the reserve levels go down faster than they can be replenished.

Hydrologists are constantly looking for ways to find more water to keep up with current demands.

Water treatment facilities take the water that has been used for waste and turn it back into fresh, local water that can be consumed again.

Hydrologists not only look for ways to improve these facilities, they also try to find new underground wells of water and, perhaps even more importantly, figure out how to maintain these supplies with the ever-growing threat of pollution.

Pollution is industrial waste, emissions from cars, runoff of pesticides and animal wastes from farms, and extra nutrients in the soils that cause an imbalance.

These can run into lakes, rivers and streams; seep into the groundwater; or collect in the air and fall back to the ground as acid rain.

Mapping the course of these contaminants through environmental hydraulics is one way hydrologists help locate and clean up pollutants.

Another way is through innovations like permeable pavement materials. When rain falls, it sometimes contains pollutants. In places with a lot of people, like most cities, there also tends to be a lot of concrete.

This washes out all of the pollutants on the road and puts them into the nearest sewer, drain system or river, which overflows with water and has no place else to go.

Concrete is impermeable -- it won't allow water to pass through it into the ground. This poses a problem, because filtering the pollutants out with rocks and sand is the first natural water filtration system for our groundwater.

One answer to this problem may be permeable concrete. This surface allows water to pass through it, sort of like soil.

It takes the pressure off of the sewage systems in urban areas where all of the water and waste have to drain during a big rain. It also helps with flood control as well as pollution control.

The costs, however, are sometimes prohibitively high. Digging up streets and replacing the concrete is no small task.

The best way to begin the process of permeable planning is to start during the planning phase of a project.

This is just one of the many ways hydrologists work to keep our ground water safe. Other hydrologists research pollution levels in snow, soil and even glaciers.

On the next page, find out how hydrologists can predict, and sometimes even prevent, floods.

Flood Control

Anyone who has ever experienced a flood or known someone who has understands that floods are serious business. They can take out entire communities and level hundreds of years of history in just seconds.

Some floods can arrive suddenly -- these are called flash floods or critical floods. Sometimes it doesn't even have to be raining anywhere nearby for a flash flood to occur.

Flash floods can happen when a heavy rain occurs upstream and the water flows downstream, gathering more momentum as it passes.

Another type of critical flooding happens when some sort of flood-retention device, like a dam or levee, breaks and water rushes out.

Non-critical floods are floods that happen slowly, over a relatively long period of time. These occur when heavy rains fall for days on end, and rivers, lakes and streams swell past their normal boundaries.

Don't let the name fool you -- non-critical floods can be just as devastating as flash floods if they're not prepared for, and they can lead to critical flooding as well.

Hydrologists work constantly to prevent and lessen the severity of floods. 

Hydroclimatologists use rainfall data and meteorological technology to help determine the maximum rainfall for an area.

They then try to determine when floods might occur and how much rain it would take to flood an area.

With this information, hydrologists work with organizations, like the  United States Federal Emergency Management Agency (FEMA), to help plan city development and emergency response. This is based on the idea that a major flood happens once every one hundred years.

A hydrologist's goal is to figure out what the worst flooding possibilities are for a span of one hundred years and design around that possibility to minimize the harm and the cost of rebuilding.

Sometimes, if the cost to build a flood device to one-hundred-year flood strength is much more than the cost of rebuilding, engineers will build for the possibility of a 25- or 30-year flood -- the worst possible flood that might happen every 25 to 30 years.

This usually happens in remote areas, like parks or forests, where there are not a lot of people who might be affected.

The work of the hydrologists determines where and how to build not just flood devices like levees, dams and culverts, but also where to put entire cities and neighborhoods.

Safety is what's most important. Successful flood control is not always apparent, but unsuccessful attempts are far too obvious.

Some hydrologists go to the ends of the Earth to study the water system -- some go even farther. Find out how far some are willing to go on the next page.

Mapping and Tools

Water is everywhere, but it's not always reachable.

Hydrologists use models, maps and figures to help them distinguish where the water is -- underground aquifers and remote glaciers are no match for a well-informed hydrologist.

Spatial hydrologists use GIS (global interface systems) and GPS (global positioning systems) to help them map streamflow, pollution and various environmental problems.

These can look like anything from a line graph to a full-scale 3-dimensional model of a river or underground water system.

These high-tech systems make use of coordinates, measurements and data to generate detailed pictures of the area.

Hydrologists will go pretty far to get information on the movement of water. Remote sensing satellites orbit the Earth, taking pictures of the oceans and what's happening in them.

The satellites produce topographical maps of the ocean, which help hydrologists study the oceans and their movements as a whole.

There's even a coral-reef remote sensing tool. Reefs are a great ecological resource, helping to produce oxygen and keep an environmental balance for the entire planet.

Knowing where these reefs are and how to study them is very important.

Parametric hydrology is a more theoretical branch of hydrology. It uses computer modeling to come up with relationships between events in the hydrological cycle.

It then uses these relationships to generate possible new events.

Overall, hydrologists are a large and diverse group. They are dedicated to the preservation of the Earth's water by any means necessary.

Hydrologists help maintain the livelihood of mankind by helping to regulate floods, pollution and sewage.

Not only that, they get to make some really fascinating models.

Hydrology is a branch of science that will always be in demand, especially as our population continues to grow and the demand for fresh water increases.

https://science.howstuffworks.com/environmental/earth/oceanography/hydrology.htm