TERM: 2ND TERM
SUBJECT: BASIC SCIENCE
CLASS: JSS 3
TOPIC: ELECTRICAL ENERGY
Electricity is the flow of electric current. Electric Current is the continuous flow of charges (electrons). It is also the rate of flow of charges. Electricity has several applications in the modern day society. Electrical energy is needed by industries, hospitals, offices, homes, schools, research institutes and so on. Power generation in Nigeria is by electricity Distribution Company of Nigeria (EDCN), which is saddled with responsibility of generating power, distribution of power and billing of power consumption.�
Concept of Electron Flow
When current is flowing in a wire, electrons are moving rapidly. Electrons have negative charges. Negative charge is usually shown with a minus sign. Electrons flow round a path called circuit.
Concept of Current, Resistance and Potential Difference
Current: current is the continuous flow of electrons. It is also defined as the rate of flow of charges. It is represented as I. It measured in ampere (A). It is measured using an instrument called ammeter. Depend on the source of generation, there are two types of current: Direct current (DC) and alternating current (AC). Direct current is gotten from small generators, batteries and inverters while the alternating current comes from the transmission lines and transformers.
Resistance: this is the opposition to the flow if electric current in a circuit.Is represented as R. It is measured in ohms with an instrument called ohmmeter. An electrical component designed to introduce a known value of resistance into a circuit is called a resistor.
Potential difference (P.D): This is the energy required to move charges from the positive terminal to the negative terminal. P.d is represented as V and measured in volt using an instrument called Voltmeter.�
Series and Parallel Arrangement in Electric Circuit.
Series Arrangement of Resistors.
Series connection is the connection of resistors from one end to another.
RT = R1 + R2 + R3
RT means total or effective resistance.
Parallel Arrangement of Resistors.
This is the arrangement in which resistors are arranged side by side such their corresponding ends join together at two common junctions.
1/RT = 1/R1 + 1/R2 + 1/R3
HOUSE CIRCUIT: FUSE AND CIRCUIT BREAKER.
220V of electricity enters our homes from the transformer and it us sent into the meter.
In order to prevent power surges or electrical problems, fuses and circuit breakers are used. A fuse is a safety device in an electric circuit. It consists of a thin resistance wire that will permit only a certain amount of electric current to pass through it, otherwise it will melt. Fuses are placed in the main electrical supply to protect wiring in the house. A circuit breaker has a switch that automatically goes off when there is an electrical problem it can be turned on later.
Billing of Electric Meter Reading
At home, electrical power is measured and billed. Power is the rate at which work is done.
Electrical power = current � voltage�
Electrical power is measured in watt using an instrument known as wattmeter.
One watt is the power consumed in an electric circuit when one joule of work is done in one second. Larger units of power are the kilowatt (kW) and megawatts (MW).
1KW = 1000 watts = 103 W
1MW = 1000000 watts = 106 W= 103 KW.
In order to bill an electric Meter, electric energy consumption is measured and sold by the Electricity Distribution Company of Nigeria (EDCN) in units of kilowatt-hour.
Example: A radio set is used for 12 hours per day for 65days. Find the quality of energy consumed and the cost, if the radio set is rated 35W. Assume that the cost of 1 kWh is 50 kobo.
Quantity of energy consumed = power � time
Energy consumed= 35W � 12hours � 65days
Energy consumed= 27300Wh
Dividing by 1000 to make it KWh = 27300Wh
Therefore, the quantity of energy consumed= 27.3kWh
Cost= quantity of energy consumed � the cost of 1 unit of energy
Cost of 1 unit of energy= 50kobo
Cost of energy consumed= 27.3kWh � 50kobo= 1365kobo= 13.65
Electric meter reading
Electric meter is a device installed in homes, industries, schools and offices to read the quantity of electrical energy used by local consumers of electricity. To read the meter, the previous unit is subtracted from the current unit, which will give the actual meter reading of the meter.
For example, if the previous unit or reading on the meter is 48,626.8 units and the current reading is 59,014.1 units, the actual meter reading for the month will be given as follows:
Current reading - Previous reading = Actual reading
50,014 - 48,626.8 = 1,387.3
Therefore, the meter reading for the month is 1387.3
GENERAL EVALUATION/REVISIONAL QUESTIONS
Precious Seeds Basic Science for JSS three by J.O otugboyega et al. Chapter 16. Pg 99-101
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