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Calculating energy costs

What is the cost of running a 0.200-kW computer 6.00 h per day for 30.0 d if the cost of electricity is $0.120 per kW h size 12{"kW" cdot h} {} ?

Strategy

Cost is based on energy consumed; thus, we must find E size 12{E} {} from E = Pt size 12{E= ital "Pt"} {} and then calculate the cost. Because electrical energy is expressed in kW h size 12{"kW" cdot h} {} , at the start of a problem such as this it is convenient to convert the units into kW size 12{"kW"} {} and hours.

Solution

The energy consumed in kW h size 12{"kW" cdot h} {} is

E = Pt = ( 0 . 200 kW ) ( 6 . 00 h/d ) ( 30 . 0 d ) = 36 . 0 kW h, alignl { stack { size 12{E= ital "Pt"= \( 0 "." "200"" kW" \) \( 6 "." "00"" h/d" \) \( "30" "." 0" d" \) } {} #size 12{" "="36" "." "0 kW" cdot "h,"} {} } } {}

and the cost is simply given by

cost = ( 36.0 kW h ) ( $0.120 per kW h ) = $4.32 per month. size 12{"cost"= \( "36" "." 0" kW" cdot h \) \( $0 "." "120"" per kW" cdot h \) =$4 "." "32"" per month"} {}

Discussion

The cost of using the computer in this example is neither exorbitant nor negligible. It is clear that the cost is a combination of power and time. When both are high, such as for an air conditioner in the summer, the cost is high.

The motivation to save energy has become more compelling with its ever-increasing price. Armed with the knowledge that energy consumed is the product of power and time, you can estimate costs for yourself and make the necessary value judgments about where to save energy. Either power or time must be reduced. It is most cost-effective to limit the use of high-power devices that normally operate for long periods of time, such as water heaters and air conditioners. This would not include relatively high power devices like toasters, because they are on only a few minutes per day. It would also not include electric clocks, in spite of their 24-hour-per-day usage, because they are very low power devices. It is sometimes possible to use devices that have greater efficiencies—that is, devices that consume less power to accomplish the same task. One example is the compact fluorescent light bulb, which produces over four times more light per watt of power consumed than its incandescent cousin.

Modern civilization depends on energy, but current levels of energy consumption and production are not sustainable. The likelihood of a link between global warming and fossil fuel use (with its concomitant production of carbon dioxide), has made reduction in energy use as well as a shift to non-fossil fuels of the utmost importance. Even though energy in an isolated system is a conserved quantity, the final result of most energy transformations is waste heat transfer to the environment, which is no longer useful for doing work. As we will discuss in more detail in Thermodynamics , the potential for energy to produce useful work has been “degraded” in the energy transformation.

Section summary

  • Power is the rate at which work is done, or in equation form, for the average power P size 12{P} {} for work W size 12{W} {} done over a time t size 12{t} {} , P = W / t size 12{P= {W} slash {t} } {} .
  • The SI unit for power is the watt (W), where 1 W = 1 J/s size 12{1" W "=" 1 J/s"} {} .
  • The power of many devices such as electric motors is also often expressed in horsepower (hp), where 1 hp = 746 W size 12{1" hp "=" 746 W"} {} .

Conceptual questions

Most electrical appliances are rated in watts. Does this rating depend on how long the appliance is on? (When off, it is a zero-watt device.) Explain in terms of the definition of power.

Explain, in terms of the definition of power, why energy consumption is sometimes listed in kilowatt-hours rather than joules. What is the relationship between these two energy units?

Questions & Answers

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s. Reply
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Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
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Do you know which machine is used to that process?
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how to fabricate graphene ink ?
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for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
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Cied
types of nano material
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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many many of nanotubes
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I'm interested in nanotube
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
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what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
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after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
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silver nanoparticles could handle the job?
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Uday
I'm interested in Nanotube
Uday
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Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Introduction to physics for vanguard high school (derived from college physics). OpenStax CNX. Oct 15, 2014 Download for free at http://legacy.cnx.org/content/col11715/1.1
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