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Practical electricity - Coggle Diagram
Practical electricity
COST OF ELECTRICAL ENERGY CONSUMPTION
why kilowatt-hour as unit for measuring electrical energy in households, industries instead joule?
amount of electrical energy consumed by households, industries very large. Unit joule very small unit, not suitable measure electrical energy consumption in households ,industries.
To find the amount of electrical energy consume
Energy consumed (
kWh
) = Power (
kW
) × Time (
h
)
To calculate the cost of electrical energy consume
Cost of electrical energy consumed (
$
) = Units of electrical energy consumed (
kWh
) × Cost per unit
CALCULATING THE COST OF ELECTRICAL ENERGY CONSUMPTION
TV power rating of 1500 W used 6 hours every day. Cost of using TV for
a week
if one unit of energy costs 25 cents?
power
= 1500 W = 1.5 kW
Time
= 6 hours a day
Time in 7 days
= 7 × 6= 42 hours
Unit cost of electricity
= $0.25/kWh
Electrical energy used
= 1.5 kW × 42 h = 63 kWh
Cost of electrical energy used
= 63 kWh × $0.25/kWh = $15.75
note:convert the unit watt (W) to kilowatt (kW).
convert 25 cents to $0.25 for easy calculation
CALCULATION INVOLVING POWER, ENERGY AND TIME
a device uses 2700 J of electrical energy in 3 minutes. What is its power?
Energy \= 2700 J
Time \= 3 min
Time must be expressed in unit second.
\= 3 × 60 \= 180 s
Power \= 2700/180 \= 15 W
a device of 0.5 W consumes 5000 J of energy. How long has the device been turned on?
Power \= 0.5 W
Energy \= 5000 J
Recall that the unit watt is J/s
Time \= 5000/0.5 \= 10 000 s
POWER
Power: rate of converting electrical energy into other forms of energy.
SI unit for power is the watt (W) or joule per second (J/s).
larger power an electrical appliance is, larger amount of electrical energy it consumes.
USING ELECTRICITY SAFELY
the main voltage supply to Singapore homes and industries is
230 V
.
fuse
circuit breakers
earth wire
protective layer has a green and yellow strips.
it is a low-resistance copper wire
connects metal casing of electrical appliances to ground.
Earthing prevent people from receiving electric shock
. No electric current flowing in under the normal conditions. Only carries electricity when live wire become faulty
contains: main switch miniature circuit breaker (MCB) earth leakage circuit breaker (ELCB)
Earth leakage circuit breaker monitors amount of current in live, neutral wires. It has electromagnetic switch which turns off electricity supply in a circuit when there is a current leakage of 30 mA or more through earth wire
a capsule contain a short length wire. Each fuse a rating of
1 A, 2 A, 5 A, 10 A ,13 A
rating of fuse should be used which is just
slightly higher
than amount of electricity flowing in a circuit under normal conditions
how it prevent electricity hazards
is found in a 3-pin plug and fuse box. It must be connected to the live wire.
too large current flowing in the circuit, wire in fuse melts, breaks circuit. Thus , open circuit, electricity stops flowing in it.
feature
each rating
allows
specific
amount of electric current flowing in
a circuit.
WIRING IN 3-PIN PLUGS
Marking
Colour
During normal functioning
Current Potential difference
Live
L
Brown
Present
High
Neutral
N
Blue
Present
Low
Earth
E
Green and Yellow
Absent
Low
Type of wire
DANGEROUS USE OF ELECTRICITY
Overloading
When too much electricity flowing in a circuit, it is called an
overload.
when too
many
electrical appliances connected
same
power outlet. results in very
large
current drawn to circuit.
conducting wires may be
overheated
, can cause
accidental fires
.
