Electrical Energy

Back to: BASIC SCIENCE JSS3

 

Welcome to class! 

In today’s class, we will be talking about electrical energy. Enjoy the class!

Electrical Energy

A conductor contains mobile electrons and these electrons are responsible for electrical conduction. Therefore, electrical energy is the work done by an electric charge (mobile electrons). Electrical energy is a result of the movement of the mobile electrons in the conductor, e.g. electric wire.

Flow of electrons

Current is a flow of electric charges. The flow of electron simply means electric current. An electric circuit, these charges are often carried by moving electron in a wire. Electrons are invincible to the eye, but the effect of the movement can be felt and measured in an electrical circuit.

There are two types of electron flow, these include:

1. Direct current
2. Alternating current

• Direct current (DC): It is a type of electron flow (electric current) in one direction. DC is the continuous movement of electrons from negative to positive. Examples of this type of electron flow can be found in batteries, solar cells, etc. It is found in many low voltage applications.
• Alternating current (AC): Alternating current is a type of electron flow (electric current) in two directions, i.e. moves from the positive terminal to the negative terminal and vice versa.

Series and parallel circuits

There are two major ways in which an electrical circuit can be set up:

• Series circuit: In the series circuit, the components are connected in chains, so that the same amount of current can pass through all the components. The total resistance of a resistor in series connection can be illustrated below:

R_{total =} R₁+R₂+ …R_n

 V_{total =} V₁=V₂=…V_n

and the current given by:

I_total   =I₁+I₂+…I_n

• Parallel circuit: In parallel circuit components are connected alone multiple paths for current to flow through so that the same amount of voltage can be applied to all components. This can be illustrated below:

The total resistance of a resistor parallel connection is given by :

R_{total =} 1/R₁+1/R₂+ …+1/R_n

 V_{total =} V₁=V₂=…=V_n

I_total   =I₁+I₂+…I_n

Ammeter and voltmeter

An ammeter is an instrument used to measure the electric current in a circuit. For a proper reading of electric current in a circuit, an ammeter must be connected in series. This is necessary because circuit in series have the same amount of current that passes through its components. Electric current is measured in ampere (A).

A voltmeter is an instrument used to measure the electric potential (voltage) in an electrical circuit. For proper reading, a voltmeter is connected in parallel. The unit of potential difference in volts(V).

Fuse and circuit breaker

Fuse and circuit breakers are devices designed to cut off power supply from the mains immediately the current accidentally becomes higher than the fuse rating. The use of fuse and circuit breakers in household wiring is very important.

Fuse: Fuse is a piece of metal having a low melting point. It melts when it is overheated. For the circuit to work again, the melted fuse must be replaced.

Circuit breaker: Circuit breaker is a device designed to strip off and makes a circuit open immediately the current accidentally becomes higher than abnormal. This device puts a stop to current flow and it has to be reset for the circuit to work again.

Electric meter reading and billing

The electric meter is a device that measures the amount of electric energy consumed by resistance or an electrically powered device. There are two kinds of electric meters, they are:

• Prepaid meter
• Postpaid meter

In Nigeria, electric utilities, such as Ikeja electric, use electric meters installed at consumer’s residence for billing purposes. They are typically calibrated in billing units, the most common billing unit used is a kilowatt-hour (kWh). The unit of power is kilowatt (kW). Therefore, the energy used over time can be expressed in watt-hour (kWh). The total energy consumed can be calculated using the formula given below:

Energy = power x time

Energy = kWh

= kWh

The cost of the energy = Energy x Cost per unit kWh.

Cost = kWh x cost (per unit kWh)

Example

Assuming the cost of one unit of energy, i.e. 1 KWh be 5 kobo. If in a house, there are:

• Fifteen 50W electric bulbs.
• One electric kettle of 500 Watt.

a) Assuming the electric bulbs are used for 5 hours for 30 days. Find the quantity of energy consumed by the electric bulbs and the cost

b). The electric kettle is used for six minutes per day for 30 days. What is the quantity of the energy consumed the electric kettle and its cost?

Solution

1. a) quantity of energy consumed

Energy =Power (kW) x Time (h)

Power consumed by the 15 bulb=

50W x 15 = 750W = 0.75kW

Time = 5hrs

Energy 0.75kW x 5h

Energy consumed by the 15 50W bulb for 30days = 3.75kWh x 30.

Total energy = 112.5kWh

The cost = Energy x cost per kWh = 112.5kWh x 5kobo

= 562.5kobo

= 5.63 Naira

1. b) The quantity of energy consumed by the electric kettle is given by:

Power = 500W = 0.5kW

Time = 6min = 0.1h

Cost per kWh = 5kobo

The total energy consumed for 30 days

= 0.5kW x 0.1hr x 30days

= 1.5kWh

The cost of the energy consumed

=1.5 x 5kobo = 1.5kWh x 0.05 naira

=7.5kobo

 

In our next class, we will be talking about Skill Acquisition.  We hope you enjoyed the class.

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