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Natural sciences

Grade 9

Energy, forces and machines

Module 22

Power

Performance (effort/work) is important, but the SPEED at which it is performed is also important.

Activity:

Explaining the concept power and calculating it

[lo 2.3; lo 2.4]

POWER = WORK / TIME

We measure this in J/s, or Watt (W)

1J per second provides 1 Watt of power

  • The term Watt is derived from the name of James Watt, who was responsible for improvements to the steam engine.
  • The electricity in your home is measured in kilowatt-hour (kWh) .
  • One kilowatt-hour is the energy output of a 1 kW appliance in one hour.
  • The longer such an appliance is operated, the more energy is used. A 2 kW heater that is operated for three hours will therefore use 6 kW energy.
  • Complete: …… kW per hour x …… hour = 6 kW.
  • The cost of a kWh varies but comes to approximately R0,35 in the Western Cape.

Assignment:

Measure your own power capacity

  • Identify a stairway in the school and measure the height of a step.
  • Multiply this by the number of steps.
  • Determine your weight.
  • Run up the stairs and take your time in seconds.

Complete the following table:

Aspect Measurement
Step height
Mass
Weight
Work performed: F x s
Time

QUESTIONS

1. What was your power?

2. Explain the following:

a) Kilowatt

b) Kilowatt-hour

3. Find out what the power rating of the average car (your educator's car, for instance) is.

4. Would you be prepared to push your educator's car all the way home? Why not?

5. Why would it be easier for the car engine to do this, even though you might have enough time and help from your friends?

6. Calculate the cost of operating a 3 000 W heater for a month (July) for 4 hours per day at a tariff of R0,35 per kWh.

Assessment of the CALCULATION of POWER CAPACITY

Were you able to apply knowledge and do the calculations?

[LO 2.3; LO 2.4]

Activity:

Doing research on power and performing relevant calculations

[lo 1.1; lo 1.2; lo 2.2; lo 2.4]

Find out what 1 kWh of electricity costs in your municipal area.

Suppose you use the following appliances during the day:

  • Computer for 2 hours
  • Television for 3 hours
  • Lamp for 4 hours
  • Kettle for 15 minutes
  • Stove for 45 minutes
  • Hairdryer for 15 minutes
  • Determine the average power of each of these items by reading the specifications given on the appliances. Complete the table.
Electrical appliance Power (kW)
Computer
Television
Lamp
Kettle
Stove
Hairdryer

Now complete the following cost assessment:

APPLIANCE POWER (kW) as above TIME Usage(hours) Energy Usage (kW/h) Cost @ R1,50 per hour
Computer
Television
Lamp
Kettle
Stove
Hairdryer

QUESTIONS

1. What is your deduction?

2. Are you aware of the need to use energy more economically? Give your own opinion of this.

3. Calculate the following:

a) A mountaineer whose mass is 75 kg climbs a 320 m rock face in 20 minutes. Calculate his power.

b) A large cupboard weighing 150 kg has to be carried up a stairway approximately 5 m high during a move.

  • How much work is performed?
  • What is the performance rating of the workers if two men are able to do this in 10 minutes?

Assessment of RESEARCH on appliances

Were you able to obtain all the required information and do the calculations?

Could you categorise information?

[LO 1.1; LO 1.2; LO 2.2; LO 2.4]

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

This is evident when the learner:

  • plans investigations;
  • conducts investigations and collects data.

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

  • categorises information;
  • interprets information;

2.4 applies knowledge.

Memorandum

Power

Activity

Questions:

Power = Labour (work) Time

Labour = Power (F) × s

Weight = Mass × 10 =  Kg

= F × s Time =

2. a) 1000 Watt, in other words, 1 000 × Joule/second

b) The amount of kW that is delivered or consumed in one hour

3. Larger cars approximately 100 kW; smaller cars approximately 70 kW

4. –

5. Engine has greater power / capacity for doing work

6. First calculate total consumption of energy (kWh):

= kW × h (hour)= 3 kW × 124 h= 372 Kw

Then calculate the costs:

= 372 × R0,35= R130,20

Activity

The power per hour of appliances (more of less):

  • Pocket calculator 0,0006W
  • Microwave oven 750W
  • Drill 500W
  • Radio 28W
  • Toaster 800W
  • Fan 100W
  • Iron 1 200W
  • Stove 1000W
  • Computer 250W

Questions:

1. The greater the power, the higher the cost of using it

2. Debate

3. a) W = F x s= (75 x 10) x 320= 750 x 320= 240 000 J

Power = 240 000 J ( 20 × 60 ) = 240 000 1 200 = 200 W ( or 0,2 lW ) alignl { stack { size 12{ ital "Power"= { { size 11{"240"`"000"`J}} over { size 11{ \( "20" times "60" \) }} } } {} #size 11{ {}= { { size 11{"240"`"000"}} over { size 11{1`"200"}} } } {} # size 11{ {}="200"`W` \( ital "or"`0,2 ital "lW" \) } {}} } {}

b) W = F x s = (150 x 10) x 5= 7 500 J

Drywing = Arbeid Tyd = 7 500 J 600 s = 12 , 5 W alignl { stack { size 12{ size 11{ ital "Drywing"= { { size 11{ ital "Arbeid"}} over { size 11{ ital "Tyd"}} } }} {} #size 11{ {}= { { size 11{7`"500"`J}} over { size 11{"600"`s}} } } {} # size 11{ {}="12",5`W} {}} } {}

 One worker's performance = 12,5  2= 6,25 W

Questions & Answers

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Akash Reply
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Maciej
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s. Reply
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Devang Reply
are you nano engineer ?
s.
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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.
Harper
Do you know which machine is used to that process?
s.
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for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
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or in general
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in general
s.
Graphene has a hexagonal structure
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Cied
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I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
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what is the function of carbon nanotubes?
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I'm interested in nanotube
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AMJAD
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Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
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AMJAD
what is system testing
AMJAD
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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I'm interested in Nanotube
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Source:  OpenStax, Natural sciences grade 9. OpenStax CNX. Sep 15, 2009 Download for free at http://cnx.org/content/col11069/1.1
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