electrical energy and power-kd4.4

7/29/2019 Electrical Energy and Power-KD4.4

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ELECTRICAL ENERGYAND POWER

ByUneh Sunarni

Adde Lisma Priyanti

Dwi Yatmi YudiprihastutiHenny Rondonuwu


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Standard Competence

Understanding theelectrical concept and its

application in daily life


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Basic Competence Describe the relationship

between electrical energyand electrical power and its

beneficial in daily life


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Objective

The students are able to :1. Explain what is the meaning of electrical

energy and its unit

2.state some electrical hazards andprecautionary measures to ensure thesafe use of electricity at home

3.Explain what is the meaning of electricalpower and its unit


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4. Solve simple problems on the cost

of using electrical appliances, usingkilowatt-hour, as a unit ofelectrical energy consumption

5. Explain the beneficial of electricalenergy and power in house holds

6. Describe the electrical energyconversion


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6. discuss the importance of reducingelectrical energy wastage

7. show an appreciation how to

economizing the electrical energy,and conserve energy


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Science words

electrical energy

electrical power


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Electrical energy

How can the batteries produceelectrical energy?


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The battery contains material that cancause chemical reaction.

The chemical reaction happens onlywhen the negative pole (zinc) isconnected to the positive pole (carbon

rod)


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When the battery is connected to theelectrical circuit a chemical reactionbetween zinc and electrolyte solution inthe battery is happens, so it produceselectron flow from the negative pole to

the positive pole through a conductorwire

The movement of electrons producesElectrical Energy


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ich lamp is more brighter?

A B

Why?

6 V 4,5V


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The lamp A has higher

electrical energy, while B haslower electrical energy.


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Components of a Circuit

PowerSource

Conductor

Load


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When the batteries are used to turn onthe lamps they work equal to theincrease of electrical energy.

The chemical energy in batteriesbecomes electrical energy and thecharges flow from a to b because ofpotential difference. So, the electrical

energy can be written as follow :

W = Q V


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W = Electrical energy (joule)

Q = Electrical charge (coulomb)V = Potential difference (volt)

Q = I t t = time (second)I = Electrical current (ampere)

W = V I t


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Exercise

1. An electrical stove having avoltage of 220 V is passed by

electrical current of 2 A. How

much is the electrical energy

used for:

a)10 secondsb)1 minute


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2.In a conductor wire, it flows

electrical current of 5 A for20 minutes. The amount of

electrical charge that flowsin the conductor wire is.


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(a) In the case of wet conditions and damagedinsulation, such as in old and frayed wiring,

What is the consequence?

metal casing becomes live

user may be electrocuted if come intocontact with metal casing.

exposed live wire

live wires become loose and make contact with themetal casing

This is especially dangerous when the human body is wet due toperspiration, high humidity or even with wet hand from the tap.

Dangers of Electricity

Safe Use of Electricity


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(b) Overloading of cables at home

What is the consequence?

When a large electric current flows through

the power outlet, plugs, and wire, overheatingoccurs, whichcan possibly cause a fire.

Having many appliances plug toone power outlet at the sametime.


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Conclusion Electrical energy is energy that produced

by the presence of electrical current in a

conductor material

Electrical energy Equation:

W = Q V or W = V I t

Dangers of Electricity:

1. In the case of wet conditions and damagedinsulation, such as in old and frayed wiring,

2. Overloading of cables at home


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Thank You

l i l


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We pay for the electrical energy used in our home, which dependson: The power output of the electrical appliance, and the time it isin use.

As the SI unit for energy, J (watt x second) is too small for thelarge amount of electrical energy, a more convenient unit, the kWh,

is used:KilowattkWh

Energy used =Power x Time

1 kWh is called 1 unit.

Electrical Power

Electrical power is the rate at which electrical energy isconverted into other forms of energy.

SI unit for power is watt (W) one joule of energy used per sec

Pay Your Electricity Bills

Go to Video 19.1

Hour


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1 kWh is

called 1unit.

Cost = Energy consumed x Cost

per unit

The cost of using electricity isgiven as:

Using & Paying forElectricity

DidYouKnow

???


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The diagram shows the information given on an electric iron.

220 V to 240 V 1000 1200 Watts

Ac only

Model XYZ

If electricity costs 16 cents per unit, what is the cost of usingthe iron at maximum power for 30 minutes everyday in May?

Cost of electricity = Energy consumed x Cost per unit

= Power x Time x Cost per unit

= 1.2 x 0.5 x 31 x 16

= 153.6 cents

= $1.54

Sample of Calculation


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Many electrical appliances obtain electrical supply from the sockets.This will connect the appliances through the power sockets to the mains.

There are mainly two types of plugs:

- two-pin plugs

- three-pin plugs (more commonly used)

In a three-pin plug, three types of wires: Live, neutral and earth, are

connected to their specified terminals respectively.

Each wire connected toL, N and E terminalsand is colour coded:

Live BROWN

Neutral BLUE

Earth Yellow Green

Socket & Plug


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A fuse is a short piece of wire, which is fitted on the live wire.

It heats up and melts when overheated, i.e., when the electric currentflowing through it is higher that its current rating.

The copper wire in each fuse is made up of different thickness:

This allow different amount of maximum current to flowthrough before it becomes overheated and melts.

The fuse rating indicates the maximum current that it cantolerate before breaking a circuit.

Fuse


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A circuit breaker works like a fuse. It breaks a circuit when

too much electric current is detected in the circuit.

The basic circuit breaker consistsof a simple switch, connected to

either a bimetallic strip or anelectromagnet.

Circuit breaker

Current through a body unbalances the active

and neutral currents, and the circuit opens.

Active wire

Neutral wire

Earth wire

Latch

Springload


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For the sake of safety, an earth wire connects the metalbody of an electrical appliances directly o the earth.

This is because, if there is an damaged insulation, suchthat the metal casing is in contact with a live wire, themetal casing will become live.

Thus, if user accidentally comes into contact with themetal casing, part of the conducting path for currentwill be formed to complete its circuit. As a result, usermay be electrocuted.

LN

Heatingelement

Earth wire

Earthing an appliance is only useful whenthe appliance has a metal casing.


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Double insulation Some appliances have casing made of insulating materials ,

such as plastics. Thus, they have double insulation.

Hand-held electrical appliance, such as hair dryer, isprotected by double insulation.

Such appliances do not have metal casing or conducting part incontact with the user. Hence, no earth wire connection isprovided.


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A consumer unit has four main safety devices:

Consumer unit

1. Main switch It is connected to the live wire from the main supply, so it connects

or cuts off the electricity supply to a whole building or a house.

2. Miniature Circuit Breaker(MCB) It is a small electromagnetic switch.

It operates like a fuse but it breaks the circuit by tripping itsswitch when the current exceeds its rating.

It contains an electromagnetic switch that breaks the circuit whencurrent flowing through the earth wire exceeds 30 mA or whenthere is faulty equipments being used.

3. Residual Current Circuit Breaker (RCCB)

4. Fuse Refer to previous slide


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19.3 Reducing Electrical EnergyWastageWe need to reduce electrical energy wastage because:

Our electricity bills will increase when the price of fuels increase Only a limited supply of fossil fuels is available

Burning of natural gases causes pollution

Ways to reduce electrical energy wastage:

Switch off electrical devices when they are not in use

Use energy-efficient electrical appliances Regular checking of refrigerators for air leakage

Service air conditioners and clean their air filters regularly

Use energy-saving bulbs instead of incandescent light bulbs

electrical energy and power-kd4.4

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