Describe the second law of thermodynamics
Most modern conversion devices - such as light bulbs and engines - are inefficient. Even natural systems must comply to this law (see Energy Through Our Lives - Section D. For example most incandescent light bulbs are only 5 percent efficient (.05 efficiency = f units of light out / 100 units of electricity in).īecause of unavoidable compliance with the second law of thermodynamics, no energy conversion device is 100 percent efficient. That is, how much of the energy is used to do what is intended (e.g., produce light) compared to how much is lost or "wasted" as heat. A formula for energy efficiency is the amount of useful energy obtained from a conversion divided by the energy that went into the conversion (efficiency = useful energy output / energy input). In terms of energy, efficiency means how much of a given amount of energy can be converted from one form to another useful form. NOTE: There are other considerations with developing and using efficient conversion devices, such as costs and government subsidies. Instead, of the 100 units that are used to generate light, 95 are needed to heat the filament. Applied to the light bulb, the second law of thermodynamics says that 100 units of electrical energy cannot be converted to 100 units of light energy. 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. The thermal energy that is produced by the light bulb is often called wasted heat, because it is difficult to use this form of energy to do work.
When the bulb is turned on, an electrical current passes through the filament, heating it up so much that it emits light. Although the quantity of energy is the same before and after conversion, the quality is different. An incandescent light bulb has a thin wire filament mounted inside it. However, not all the energy is converted into the desired form of energy (such as light). This may suggest that we could always convert energy to whatever forms we need without ever worrying about using up our energy resources. The First Law of Thermodynamics states that energy can neither be created nor destroyed, it can only be converted from one form to another. Energy Efficiency and the Second Law of Thermodynamics