This document discusses analyzing electrical energy and power. It defines electrical energy as the energy released when electric charges flow through any two points in an electric circuit. Electric power is defined as the rate at which electrical energy is released. Formulas are provided for calculating electrical energy, power, current, and resistance in various circuits. Examples problems are given and solved for finding current, energy usage, and cost based on power ratings and time. The concepts of power rating, energy consumption, and energy efficiency are compared for different electrical appliances. Ways to increase energy efficiency such as using efficient lighting and appliances and eliminating wasted energy are described.

1. 2.5 analysing electrical energy
and power

2. Learning objective
• Analysing electrical energy and
power

3. Learning outcomes
• Difine electrical energy
• Define electric power
• Solve problems involving electrical energy and
power
• Compare power rating and energy consumption
of various electrical appliances
• Compare various electrical appliances in terms of
efficient use of energy
• Describe ways of increasing energy efficiency.

4. Electrical
energy
The energy released when electric charges flow
through any two point in an electric circuit
UNIT :
Joule (J)
E = VQ
E = VIT E = I²Rt
E = V²t
R

5. ELECTRIC
POWER
Defination: the rate at which
electrical energy is released
P = E
t
P = V I P = I ² R
P = V ²
R

6. Question 1
An electric kettle is connected across a 240
V power supply. If the resistance is 40Ω,
calculate
a. The current flowing through the
element.
b. The quantity of heat produced in 10
minutes.
[ans : a. 6A, b. E = 864 kJ]

7. Question 2
A filament lamp is labelled “12V, 36W”. If
the lamp is connected to a 12V power
supply, calculate
a. The current that flows through the
lamp,
b. The amount of electrical energy used by
the lamp in 30 minutes.
[ ans : a. 3A, b. 64.8 kJ]

8. Power rating and energy consumption
The amount of electrical energy it uses
per second
Energy = power x
time
E = P t
Energy = power x time
1 kWh = 1 kW x 1 h
= 1000 x 60 x
60
= 3 600 000 J1 kW h = 1 unit
Cost = number of units x cost per unit

9. TNB electricity meter

10. Tariff rate
The cost for one unit of electricity

12. Question 1
If one unit of electricity costs 21.8 cents,
calculate the cost of using five 36 W
fluorescent lamps and a 120W television if
they are switch on five hours a day for the
month of January.
[ ans : RM10.14]

13. Question 2
• A room air conditioner rated at 1 500 W is
turned on eight hours a day. How much would
you have to pay at the end of 31 days if the
tariff rates are as shown in table below.
• [ans : RM 93.31]

14. Energy efficiency
Efficiency = output power X 100%
Input power

15. Question 1
A lamp is marked “ 240 V , 100W” .
What is the efficiency of the lamp if
it produces a light output of 12 W?
[ans : 12 %]

16. Increasing Energy Efficiency
• Use more energy efficient lighting
Incandescent bulb Compact fluorescent bulb

17. Replace or clean air conditioner filters

18. Use electrical appliances wisely
Iron clothes Wash clothes

19. Eliminate wasted energy

20. Choose energy efficient appliances

21. Boost energy efficiency

23. Question
Table shows the characteristics of materials that can be
used for making a heating element.
Explain the suitability of each characteristic in Table.
Determine the most suitable material to be used for
making the heating element for an electric kettle
material characteri
stic
Melting
point/ ºC
resistance Oxidation
level
Density/k
gms¯¹
S 650 6.0 High 2900
T 550 5.5 Low 3150
U 50 10.0 Moderate 18 500
V 350 15.0 High 7400
W 200 7.0 Low 8000

24. Characteristic Explanation
High melting point So that the element does not
melt easily during the heating
process
Low resistance Allows for a larger current to
flow through it and produce a
considerable amount of heat
Low oxidation To prevent oxidation
Low density To make the kettle portable
Material T is selected.
It has a high melting point, low resistance, low
oxidation level and low density

25. Question 2
Diagram shows an electric kettle
which is labeled “240V, 1000W”
a. What is meant by
i. 1000 W
ii. The power rating of “240 V ,
1000W”
b. State one suitable material that can
be used as the heating element of
the kettle.

26. Answer
(a)(i) 1000 W is the electrical power of
the kettle which consumes 1000 Joules
of energy per second.
(II) the power rating indicates that
the kettle releases 1000 J of energy per
second when 240 V is supplied to it.
(b) Tungsten / Nichrome