Like this presentation? Why not share!

# Power

## by meenng on Sep 17, 2007

• 3,668 views

### Views

Total Views
3,668
Views on SlideShare
3,632
Embed Views
36

Likes
1
136
0

### 3 Embeds36

 http://s3smtpm5.wikispaces.com 29 http://www.slideshare.net 6 http://translate.googleusercontent.com 1

### Categories

Uploaded via SlideShare as Microsoft PowerPoint

## PowerPresentation Transcript

• Power
• Specific Instructional Objectives
• At the end of the lesson, students should be able to:
• Show understanding of the concept of Power
• Show understanding of how Power relates to Energy or work done
• Solve problems involving power
• Power
• Power is the rate of doing work.
• This means the amount of work done in one unit of time, usually in 1 second.
• It can also mean the rate of change of energy from one form to another.
• Power
• Formula, by definition can be:
• Power = Work Done or Energy
• Time Time
• P = W or E [ J ]
• t t [ s ]
• SI Unit for Power : Watt [W]
• (where W = F x s)
• (where E can be KE or PE or change in energy)
• Eg. of Power
• A wooden crate is pushed by a workman with a constant force of 300 N for a distance of 20 m in 1 minute. Find the power exerted by the man.
Work done, W = F  s = 300  20 = 6000 J Power = W/t = 6000/60 = 100 W
• Eg. of Power
• Your hifi system is rated at 1200W. Find the amount of energy generated in 1 minute.
Power = E/t = 1200 Energy generated, E = 1200  60 = 72000 J = 72 kJ Note: (convert 1 min to sec)
• Eg. of Power
• A light bulb has a rating of 230V, 20W. Find the energy generated by light bulb when switched on for an hour.
Power = E/t = 20 Energy generated, E = 20  60  60 = 72000 J = 72 kJ Note: (convert 1 hour to sec)
• Rating of electrical items
• What do you understand by ratings of electrical items like hifi systems, light bulbs, florescent tube, kettle, etc…
• Note that ratings are stated with 2 quantities: Voltage and Power. See light bulb example : 230V 20W.
• It means that the item is able to generate a maximum of 20W of power when voltage supplied to light bulb is 230V.