SPM Malaysia Physics Syllabus Chapter 7: Electricity Part 5: Electrical Energy and Power

1. Chapter 7: Electricity
Electrical Energy and Power

2. The ability of
the electric
current to do
work

3. Electrical Energy
Supplied by a source of electricity
Such as a cell or battery
When current flows in a closed circuit

4. Electrical Energy
Converts into other forms such as:
heat light mechanical
By electrical appliances when current flows in it

5. Potential Difference, V
Energy, E transferred
by 1 C of charge, Q
that moves between
two points

6. Current
Rate of charge flow

7. Combining these two equations, we get

9. Power
Unit = Watt (W)

11. An Electric Kettle
Marked
240 V 1500 W
Means that the
kettle consumes
1500 J of
electrical energy
every second its
connected to 240 V

12. The larger the
power rating,
the more energy
consumed in
every second.
The longer the
usage time,
the more
electrical
energy is
consumed.

13. 1 kilowatt-hour
(kWh)
The amount of energy
consumed by an
electrical appliance
In 1 hour
At the rate of 1 kilowatt

14. 1 kWh = 1 unit of energy
1 kWh 3.6 x 106 J
1 kW x 1 hr
100 W x 3600 s

15. Efficiency Percentage of output
power to the input
power

16. The efficiency of an electrical appliance
Is always less
than 100%
Because some energy is lost
the form of heat and sound

17. Energy Efficiency
Using energy efficient devices to gain a higher
level of useful outputs using less input

18. Increasing energy efficiency
Reduces costs
And also assisting
in energy
conservation

20. Energy efficient lightings
Use compact
fluorescent bulbs
instead of regular
incandescent
bulbs

21. Utilize electrical appliances wisely
Run washing
machines on
full load only

22. Utilize electrical appliances wisely
Iron clothes in
bulk (i.e. several
pieces at a time)

23. Utilize electrical appliances wisely
Limit usage or air
conditioning and
lighting
Switch them off
when you leave
the room

24. Utilize electrical appliances wisely
Clean air filters in air conditioners and
clothes dryers regularly

25. Utilize electrical appliances wisely
Defrost refrigerators regularly – so that
your freezer don’t work so hard

26. Utilize electrical appliances wisely
Improve
ventilation and
air flow
Better ventilation
reduces cooling
load of air
conditioners

27. A fuse – a short piece of thin wire
Which overheats when current above a
certain value flows through it

28. The fuse melts when a current that is
too high flows during a short circuit
This prevents overheating of the wire
which would cause a fire

29. If power rating of an appliance is
960 W and 240 V, then normal current = 4 A
Fuse to be used must be of higher
current:- so use 5 A fuse

30. Earth Wire, E
Three Pin Plug (green)
Safety wire –
connects appliance
to earth
Live Wire, L
(brown)
Neutral Wire, Current flows
N (blue) through circuit
Zero Potential
Difference

31. Three Pin Plug If a Live Wire
touches the metal
body of the appliance,
a large current
would immediately
flow to the earth
and breaks the fuse.
This will avoid
someone from being
electrocuted.

32. Pic credits
• Flickr / Plug Face - Day 3/365 / Jake Mates • Flickr / 148:365 - 09/25/2012 - Blown Fuse / Shardayy
• Flickr / Plasma 5/ limowreck666 • Flickr / Con – Fused / canonsnapper
• Flickr / Pedagaggi Wind Turbines / Sebastiano • Flickr / Wiring a Plug / tjmwatson
Pitruzzello
• Flickr / Dying moments / limowreck666
• Flickr / defying murphy’s law / vakas
• Flickr / Vintage Blackboard / pareerica
• Flickr / Ultraman + Mt. Fuji = JAPAN / emrank
• Flickr / kettle / butkaj.com
• Flickr / March of the washer-dryers /
Worldislandinfo.com
• Flickr / 3D Green Energy / StockMonkeys.Com
• Flickr / Electric Fuel Cap - RAC Future Car Challenge /
Dominic Alves
• Flickr / Fluorescent Tube / jeancliclac
• Flickr / 154/366 / hannah8ball
• Flickr / untitled / John Steven Fernandez
• Flickr / kitty TV / kassandrapoised
• Flickr / Universal Iron and Drapery / firexbrat
• Flickr / Only in Egypt / mnadi
• Flickr / This means you!! / passiveaggressivenotes
• Flickr / thefreezerstaresatme / expressionposthumus
• Flickr / cityswing / i_gallagher
• Flickr / made in england / fishyfish_arcade