According to the first law of thermodynamics, energy may be transferred from place to place or transformed into different forms, but it cannot be created or destroyed. The transfers and transformations of energy take place around us all the time.
Light bulbs transform electrical energy into light energy. Gas stoves transform chemical energy from natural gas into heat energy. Plants perform one of the most biologically useful energy transformations on earth: that of converting the energy of sunlight into the chemical energy stored within organic molecules [link]. Some examples of energy transformations are shown in Figure.
The challenge for all living organisms is to obtain energy from their surroundings in forms that they can transfer or transform into usable energy to do work. Living cells have evolved to meet this challenge very well. Chemical energy stored within organic molecules such as sugars and fats is transformed through a series of cellular chemical reactions into energy within molecules of ATP.
Energy in ATP molecules is easily accessible to do work. Examples of the types of work that cells need to do include building complex molecules, transporting materials, powering the beating motion of cilia or flagella, contracting muscle fibers to create movement, and reproduction.
However, the second law of thermodynamics explains why these tasks are harder than they appear. In every energy transfer, some amount of energy is lost in a form that is unusable. In most cases, this form is heat energy. Thermodynamically, heat energy is defined as the energy transferred from one system to another that is not doing work. For example, when an airplane flies through the air, some of the energy of the flying plane is lost as heat energy due to friction with the surrounding air.
This friction actually heats the air by temporarily increasing the speed of air molecules. Likewise, some energy is lost as heat energy during cellular metabolic reactions. This is good for warm-blooded creatures like us, because heat energy helps to maintain our body temperature.
Strictly speaking, no energy transfer is completely efficient, because some energy is lost in an unusable form. An important concept in physical systems is that of order and disorder also known as randomness. Overall, the goal is to reduce the amount of energy lost to increase efficiency. As well, collisions that are inelastic refer to collisions where there is some "loss" of energy during the collision. For more information on inelastic collisions, see HyperPhysics.
Electricity use is a good example that illustrates energy loss in a system. By the time the energy associated with electric power reaches the user, it has taken many forms. Initially, the process begins with the creation of the electricity through some method. For example, the burning of coal in a power plant takes the chemical energy stored in the coal and releases it through combustion, creating heat that produces steam. From here the steam moves turbines and the mechanical energy here turns a generator to produce electricity.
Further losses occur during the transport of this electricity. This electricity could reach an incandescent light bulb wherein a thin wire is heated until it glows, with a significant amount of energy being lost as heat, shown in Figure 1.
The energy that is wasted when a light bulb shines exemplifies the second law of thermodynamics that states that with each energy conversion from one form to another, some of the energy becomes unavailable for further use.
Applied to the light bulb, the second law of thermodynamics says that units of electrical energy cannot be converted to units of light energy. Instead, of the units that are used to generate light, 95 are needed to heat the filament. NOTE: There are other considerations with developing and using efficient conversion devices, such as costs and government subsidies. In terms of energy, efficiency means how much of a given amount of energy can be converted from one form to another useful form.
That is, how much of the energy is used to do what is intended e. For example most incandescent light bulbs are only 5 percent efficient. Because of unavoidable compliance with the second law of thermodynamics, no energy conversion device is percent efficient. Energy Flow in Ecosystems. Most modern conversion devices -- such as light bulbs and engines -- are inefficient. The amount of usable energy that results from the conversion process electricity generation, lighting, heating, movement, etc.
In fact, of all the energy that is incorporated into technologies such as power plants, furnaces, and motors, on average only about 16 percent is converted into practical energy forms or used to create products.
Where did the other 84 percent go? Most of this energy is lost as heat to the surrounding atmosphere. One reason is when light bulbs and other conversion devices were first invented, energy supplies seemed abundant and there was not much concern for the waste heat they generated as long as their primary purpose light, movement, and electricity was accomplished.
However, as it is becoming apparent that the energy supplies -- primarily fossil fuels -- that we use are indeed limited, one goal of technology has been to make conversion devices and systems more efficient.
The light bulb is one example of a conversion device for which more efficient alternatives have been developed. One alternative, the compact fluorescent light bulb CFL , was commercially introduced in the 's. Instead of using an electric current to heat thin filaments, the CFLs use tubes coated with fluorescent materials called phosphors that emit light when electrically stimulated.
Even though they emit the same amount of light, a watt CFL bulb feels cooler than a watt incandescent light bulb. The CFL converts more electrical energy into light, and less into waste heat.
Typical CFLs have efficiencies between 55 and 70 percent, making them three to four times more efficient than typical incandescent bulbs with efficiences under 20 percent.
Another alternative, the light emitting diode LED , has become more mainstream and affordable in recent years. LED's bring currents with a positive and negative charge together to create energy released in the form of light. LED's have efficiencies between 75 and 95 percent, making them four to five times more efficient than incandescent bulbs.
Origin of Cells 6. Cell Division 2: Molecular Biology 1. Metabolic Molecules 2. Water 3. Protein 5. Enzymes 6. Cell Respiration 9. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1.
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