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Electricity - Coggle Diagram
Electricity
How Are Current, Voltage and
Resistance Measured?
Using a Multimeter to Measure Current
•Current is the rate of flow of electrical
charges in a closed circuit. Symbol for
current is I.
•The unit of current is ampere and its
symbol is A.
•Another unit of current is milliampere and
its symbol is mA. The milliampere can be
used as a unit for smaller values of current.
Using a Multimeter to Measure Resistance
•Resistance opposes current in a circuit. The higher the
resistance → the lower the current passing through it.
•The unit of resistance is ohm and its symbol is Ω.
Another unit of resistance is kiloohm and its symbol is
kΩ.
•Electrical components have resistance. Some electrical
components have higher resistance than others.
•Resistors are specific kind of electrical components
that provide resistance. Two types of resistors fixed
resistors and variable resistors.
•A multimeter can be used to measure the resistance of electrical
components.
•The figure below shows how a multimeter is connected to measure the
resistance of a fixed resistor. There is no electric cell or other power
source connected to the resistor when a multimeter is used to measure
learning outcome
At the end of the topic, you will be able to:
•explain the advantages of connecting household appliances in parallel
• identify voltage rating and power rating found on a label of an electrical appliance
• recall and apply the relationship power = current x voltage to solve problems
• calculate the cost of using electrical appliances where the energy unit is the kW h
• identify electricity usage found on an electricity bill
•state some ways to reduce electrical energy wastage in daily lives (e.g. use energy-efficient
appliances)
•demonstrate ways and appreciate the need to reduce energy wastage
•appreciate science for its usefulness in improving quality of life: knowledge of electricity helps
us power machines
– What Is Electrical Power?
Voltage and Power Ratings
•Power is commonly expressed in the unit of watt with the
symbol W. Another unit of power is the kilowatt with the
symbol kW, where 1 kW = 1000 W.
•Electrical appliances convert electrical energy into
different forms of energy that we need. Different electrical
appliances can have different voltage ratings and power
ratings.
•We can find the voltage ratings and power ratings of
electrical appliances on their information labels.
Voltage Rating
•The voltage rating tells us the voltage the appliance is designed to be used
with.
•At the voltage stated in the voltage rating, the current passing through
the appliance will be sufficient for it to function properly. If the appliance is
used with a higher voltage, the current passing through it would be too
large and may damage it.
•Appliances with a higher or lower voltage rating than the mains supply will
need a transformer to increase or decrease the voltage from the mains
supply for the electrical appliance to be used safely.
Power Rating
•With a power rating of 1200 W, the electrical
appliance will convert 1200 J of electrical energy to
other energy forms in one second.
•The table shows the power ratings of some
electrical appliances. These ratings will vary
between brands and models of the same type of
appliance.
How Can We Determine Our Electricity Usage and
Reduce Electrical Energy Wastage?
Using Electrical Power to Calculate the Cost of Electricity Use
•Electrical energy can also be represented in the unit of kilowatt-hour with
the symbol kWh. The kilowatt-hour is used instead of joules as it is a unit
for larger values of energy that we typically use in a household.
•Electrical energy used by an electrical appliance formula
Energy (kWh) = Power(kW) x Time(h).
•Cost of electrical energy used by an electrical appliance formula
Cost of electrical energy used = Energy (kWh) x cost of energy per kWh($)
Reducing Electrical Energy Wastage
• In Topic 1 Energy, we have learnt that a large proportion of electricity is generated
by the burning of fossil fuels.
• To reduce the cost of electricity and conserve fossil fuels, we should reduce
electrical energy wastage.
• One of the ways to reduce electrical energy wastage is to use energy-efficient
appliances.
• In Singapore, air-conditioners, refrigerators, clothes dryers, televisions and light
bulbs come with an energy label to inform consumers of the energy efficiency
rating of the appliance.
• An appliance with more ticks on its energy label has higher energy efficiency.
Using appliances with higher energy efficiency can reduce electrical energy
wastage.
• We can do our part to reduce electrical energy wastage at home by:
oreducing the use of electrical appliances
ousing electrical appliances that use less electrical energy