26.9:
Electrical Energy
Electrical energy can be defined as the energy caused by the movement of electrons from one point to another.
The amount of electrical energy can be determined by the power used by a device over a specific time interval.
The SI unit of electrical energy is the joule, or watt-second, whereas the commercial unit is the kilowatt-hour, also known as the Board of Trade unit.
Consider a 60 Watt incandescent bulb and a 20 Watt LED bulb, each producing an equivalent amount of light.
Determine the cost savings in replacing the incandescent bulb with the LED bulb running for 4 hours daily for 365 days, assuming 12 cents per kilowatt-hour is the average energy rate charged by the power company.
First, individually determine the amount of electrical energy consumed by the incandescent bulb and the LED bulb.
Second, multiply the energy consumed by the individual bulb by the cost charged by the power company.
The LED bulb uses three times less energy and saves about $7.00 compared to the incandescent bulb.
26.9:
Electrical Energy
Using electric appliances for a longer period of time consumes more electrical energy and results in a higher electric bill. The energy produced by the transfer of electrons from one point to another is known as electrical energy. If power is delivered at a constant rate, the electrical energy can be defined as the product of power used by the device for a period of time. The energy unit on electric bills is the kilowatt-hour, where one kilowatt-hour is equivalent to 3.6 × 106 joules. The electrical energy (E) used can be reduced either by reducing the time of use or by reducing the power consumption of that appliance or fixture. This not only reduces the cost but also results in a reduced impact on the environment.
Lighting consumes about 20% of the energy used at home, and closer to 40% in commercial buildings. The efficiency of fluorescent lighting is approximately four times greater than that of incandescent lighting, and this is true for both long tubes and compact fluorescent lights. The heat transfer from these compact fluorescent lights (CFLs) is less, and they last up to 10 times longer than incandescent bulbs. Modern white light emitting diode (LED) lights, which consist of a number of tiny LED bulbs grouped together, are even more effective and last five times as long as compact fluorescent bulbs.
The simplest way to lower energy usage in homes and commercial buildings is to switch from incandescent to CFL or LED light bulbs. CFL bulbs operate with a much different mechanism than incandescent lights and contain argon and mercury vapor housed within a spiral-shaped tube. They use a "ballast" that increases the voltage used by the CFL bulb. The ballast produces an electrical current, which passes through the gas mixture and excites the gas molecules. The excited gas molecules produce ultraviolet (UV) light, which in turn stimulates the fluorescent coating on the inside of the tube. This coating fluoresces in the visible spectrum, emitting visible light. Whilst these bulbs do contain mercury, which is poisonous, the mercury will never be released so long as the bulb does not break. Even if the bulb does break, the mercury tends to remain in the fluorescent coating. It's a very small amount, and the benefit of saving energy may outweigh the drawback of using mercury.
Suggested Reading
- OpenStax. (2019). University Physics Vol. 2. [Web version], Pg 396 – 398. Retrieved from https://openstax.org/books/university-physics-volume-2/pages/9-5-electrical-energy-and-power